A Monograph on the Sub-class Cirripedia (Volume 2 of 2) The Balanidæ, (or Sessile Cirripedes); the Verrucidæ, etc., etc. (part 3 of 5)

A Monograph on the Sub-class Cirripedia (Volume 2 of 2) The Balanidæ, (or Sessile Cirripedes); the Verrucidæ, etc., etc. (part 3 of 5)

General Appearance.--Shape conical, either steep or considerably depressed; sometimes tubular; orifice either nearly entire or deeply toothed, not large, varying from rhomboidal to rounded-trigonal. Surface of shell smooth, never ribbed, generally naked, but occasionally the yellowish epidermis is persistent; in the same individual, I have seen all the lower part of the shell thus covered and the upper part naked, the line of separation being defined. The colour varies much, even sometimes considerably on the same individual; generally white or pale gray, with dull violet-coloured, longitudinal, moderately broad stripes; these stripes are sometimes equidistant, but more usually they are arranged so as to leave broad white spaces; the stripes fade away by endless variations, the edges of the compartments and the carinal end of the shell longest retaining any colour, until we have a uniformly white shell, generally covered with a yellowish epidermis; or the white is longitudinally marked with hyaline lines; this latter variety has a very peculiar aspect, and I did not doubt it was specifically distinct, until, in a number of specimens on a ship from the West Indies, I got the most perfect series, and another scarcely less perfect series from the Mediterranean, graduating into common coloured varieties. Rarely the dull violet or purple stripes become approximate and dark, so that the whole shell is tinted of a brownish slate-colour, occasionally freckled with white. Again, we have another set of very pretty varieties, with a white or very pale pink ground, with either narrow bright pink or broad pinkish-purple stripes. Again, I have seen numerous specimens of a variety, var. Stutsburi, from the west coast of Africa, in which the upper part of the shell is white, and the lower part shaded with pinkish or dark purple approximate stripes, which often become confluent; in one group, the whole shell being thus uniformly coloured, without any vestige of stripes. I have seen another group from an unknown locality, in which the lower part of the shell was uniformly blueish-gray. A variety from Australia has narrow approximate dark claret-coloured stripes, transversely freckled with white. Lastly, in the variety cirratus, the whole shell is very pale purplish-brown, with indistinct longitudinal brownish stripes, transversely freckled with white lines. I considered this as a distinct species, until quite lately finding forms which I could not possibly determine whether to class as B. cirratus or amphitrite.

The radii are generally snow-white, or freckled with a bright mahogany tint, or rarely clouded with purple, or in the pink varieties with pink. The scuta are dull purple or pink, generally with a white band along their tergal margin; often, however, they are white, with merely one or two purple fasciæ. The thickness or strength of the shells varies much; some specimens attached to a floating cane, from Natal and the Philippine Archipelago, were extremely strong; others, from the Mediterranean and Australia, and some tubular varieties from the West Indies, were very thin, translucent, and fragile. Size: large specimens generally attain a diameter of from half to three quarters of an inch in basal diameter; and I have seen one or two specimens an inch in diameter.

Scutum; sometimes the surface is very smooth, but generally the growth-ridges are moderately prominent; the latter are occasionally very finely beaded, and this seems always the case with var. cirratus. Internally, the articular ridge is prominent and reflexed: the adductor ridge is sharp, very prominent, and straight; it runs parallel to the occludent margin; close to its lower side there is often a depression (Pl. 5, fig. 2 i), sometimes bounded by a slight ridge, as if for the attachment of a muscle, but there certainly is no muscle here: rarely the adductor ridge is only slightly prominent: there is a small and shallow little pit of variable depth for the lateral depressor muscle.

Tergum (2 k-2 o); this valve is here far more variable than in any other species: in the commonest purple-striped forms (2 l), the valve is rather broad, the basal margin lies in nearly a straight line on the opposite sides of the spur, which is placed at rather less than its own width from the basi-scutal angle; the spur is rather short, and in width about one fourth of the entire valve; its lower end is either bluntly pointed or more commonly nearly square (2 k) and parallel to the basal margin: in young specimens it is generally sharper than in older ones. Externally, in the line of the spur, there is either a slight longitudinal depression, or more rarely a deep furrow. The carinal margin is more or less convex, and is formed by upturned lines of growth: the scutal margin is broadly inflected. Internally, the articular ridge in the upper part is very prominent: the crests for the tergal depressor muscle are moderately prominent, but very variable. Sometimes the carinal portion of the basal margin is slightly hollowed out. In var. Stutsburi (2 m, 2 n, 2 o), and in some white varieties, which differ most in the shape of the tergum from the commoner varieties, the whole valve is narrower, the spur is much sharper and narrower, the carinal half of the basal margin is much hollowed out and slopes down towards the spur, with the crests for the depressor muscles depending beneath the basal margin, and with the carinal margin sometimes extremely convex or protuberant. But the shape and position of the spur, and the outline of the carinal half of the basal margin vary much in nearly all the varieties.

Compartments.--The upper parts of the parietal pores are either filled up solidly with, generally coloured, shell, or they are crossed by thin transverse calcerous septa: the longitudinal parietal septa occasionally bifurcate at their bases close to the outer lamina, making an irregular outer row of minute pores. The Radii have their septa rather fine, and finely denticulated on both sides, but sometimes only on the lower side; the thickness of the septa varies a little; the interspaces are filled up solidly; the summits of the radii are jagged and oblique, and usually form an angle of about 45° with the basis, not being added to above the level of the opercular membrane; but not rarely they reach up much higher, and are very nearly parallel to the basis, extending from tip to tip of the compartments. Again, in some ordinary varieties, and always in var. Stutsburi, the summits of the radii are extremely oblique, the radii themselves forming a mere border to the compartments to which they belong. In no other species have I seen so great an amount of variation in the form of the summits of the radii. The alæ, in like manner, have their summits either very oblique, not being added to above the opercular membrane, or they are only slightly oblique; it often happens that in those specimens in which the summits of the radii are nearly parallel to the basis, the alæ are very oblique, and the converse: in other individuals, both radii and alæ have equally oblique summits. The sutural edges of the alæ vary in thickness, being either very thin and obscurely crenated, or moderately thick and ribbed. The basis is porose; but I have never seen an underlying cancellated layer of shell, as is so common in several species.

Mouth: labrum, with from four to eight, generally with six, little teeth: mandibles with three teeth, and two minute lower teeth, or mere knobs: maxillæ with the edge straight, or with the inferior part forming a slightly step-formed projection. Cirri: the rami of the first pair are unequal by three or four segments, but in some specimens by five or six segments, with the front surfaces of the segments in the shorter ramus extremely protuberant. The second pair of cirri are short, with the front surfaces of the segments moderately protuberant: the third pair have a tuft of bristles at their bases on the thorax. The segments in the sixth pair have from four to six pairs of spines on the segments; equal-sized specimens seem to vary in this latter respect. There is a small sharp projection on the dorsal base of the penis.

Varieties.

With respect to var. 1, communis, I have nothing further to remark, except that I have seen specimens identically similar from the Mediterranean, Natal, the Philippine Archipelago, and Sydney; at the latter place it is said to be rare, but in most places it is the commonest variety, and is often attached to ships' bottoms. Of var. 2, venustus, I have seen specimens from the west coast of Africa, Natal, and Ceylon, in groups by themselves, and associated with var. communis; it is much less common than var. 1. The third variety, pallidus, is not uncommon; I have seen many specimens from the bottoms of ships, from the West Indies, and the west coast of Africa. Of the var. 4, niveus, I have seen the most perfect graduated series passing into var. 1, both from the West Indies, Florida, and the Mediterranean: I have seen other specimens from the Red Sea and Madagascar. Of the var. 5, modestus, I have seen only one group from an unknown locality; it is only remarkable from its uniform colouring. The var. 6, Stutsburi, is more remarkable than the foregoing; until quite lately I did not doubt that it was specifically distinct; but as I have seen every character graduate into other varieties, I am now convinced that it is not a true species: all the specimens which I have seen have come on shells, or on ships' bottoms, from West Africa. Of var. 7, obscurus, I have seen three or four groups of specimens from unknown quarters, both on pebbles, shells, and on cork (probably from the Atlantic ocean); and likewise some specimens taken from the bottom of Her Majesty's ship "Fly," on the east coast of Australia; these latter are intermediate in character with the next var. variegatus; from the Australian seas, which I at first ranked as an undoubted species, but I have subsequently failed in discovering any sufficient diagnostic character. Lastly, of var. cirratus, I have seen several groups of specimens from India and the Philippine Archipelago, and a group intermediate in character between this and the first and third varieties, from Australia; I retained this variety owing to its peculiar freckled, pale brown colouring and beaded scuta (of which, however, I have seen decided traces in the common variety), as a distinct species, after I had given up all the foregoing forms. I entertain some doubts whether I have now acted right; but when I found some specimens which, I found it impossible to decide, whether to rank as amphitrite or cirratus, I determined to take the more prudent course, and sink the latter as a species. This variety, also, seems to connect B. amphitrite and concavus very closely.

20. BALANUS PŒCILUS. Pl. 5, fig. 3 a, 3 b.

Shell dull red, freckled with white. Scutum internally without an adductor ridge; tergum with the spur, sharply truncated, almost one third of width of valve.

Hab.--West coast of South America, Mus. Cuming; attached to an Avicula.

The appearance of the fragile shell, in the one group of specimens which I have seen, leads me to suspect that they may have grown under unfavorable circumstances. This species differs considerably in general aspect, but not much in essential characters, from B. amphitrite; the absence, however, of an adductor ridge to the scutum, and the sharply truncated spur of the tergum, are sufficient to distinguish them. In the opercular valves this species comes near to B. vinaceus, also from the west coast of South America; but the striated scuta of that species, the cancellated inner lamina of the parietes, the general colouring, and square porose radii, are amply diagnostic characters.

General Appearance.--Shell fragile, tubulo-conical, orifice large, passing from diamond-shaped into oval. Colour fine dark rose, freckled with transverse, sharply pointed, fine zig-zag white lines: the pink is also so arranged as to obscurely give to the walls a longitudinally striped appearance: radii generally rather whiter than the walls, and similarly freckled: terga similarly freckled: scuta dull red, with a white band along the scutal margin. Basal diameter of largest specimen half an inch.

Scutum, externally smooth: internally, articular ridge moderately developed, slightly reflexed: there is no adductor ridge: there is a distinct pit for the lateral depressor muscle. Tergum, with the scutal margin unusually prominent, toothed: longitudinal furrow shallow, the edges apparently having no tendency to fold in: spur short, barely one third of width of valve, with the lower end sharply truncated, parallel to the basal margin: articular ridge and crests for the depressores moderately prominent.

Compartments.--Walls very fragile, with the outer lamina not thicker than the inner lamina. Radii fragile, broad, with their summits moderately oblique; their sutural edges have the septa plainly denticulated on both sides, with the interspaces filled up solidly nearly to the tips of the septa. Alæ, with their summits more oblique than those of the radii; their sutural edges smooth. Basis with an underlying cancellated layer. Mouth: labrum with three unusually large teeth on each side of the notch: mandibles with the fourth tooth tolerably well developed, the fifth being confluent with the inferior angle. Maxillæ simple. Cirri,--first pair with one ramus longer by about four segments than the other ramus, which has considerably protuberant segments: second pair with segments only moderately protuberant: sixth pair with segments much elongated, but bearing only four pairs of spines.

21. BALANUS EBURNEUS. Pl. 5, fig. 4 a-4 d.

BALANUS EBURNEUS. Aug. Gould (!). Report on the Invertebrata of Massachussetts, 1841, fig. 6.

Shell yellowish white. Scutum striated longitudinally: tergum with the spur truncated, the basi-carinal margin generally much hollowed out, and the carinal margin protuberant in the upper part.

Hab.--United States, from about lat. 42° to Charlestown; West Indies; Honduras; Venezuela; attached to shells and floating wood. Attached to ships' bottoms from Trinidad and Jamaica, associated with B. tintinnabulum, amphitrite, and improvisus. Brackish water, Salem, Massachussetts, according to Mr. Stimpson. Mus. Aug. Gould, Agassiz, Stutchbury, Cuming, W. Dunker, &c.; very common.

General Appearance.--Shell conical, or almost tubular; white, with the surface very smooth, covered by thin yellowish epidermis, but with the radii naked. Orifice large, passing from rhomboidal into pentagonal, moderately toothed. Average full size, about one inch in basal diameter; I have seen a specimen 1.3 in basal diameter, and the same in height.

Scutum, plainly striated longitudinally: the teeth on the occludent margin small. Internally, the upper surface is roughened: the articular ridge is prominent, and either slightly or not at all reflexed: the pit for the adductor muscle is distinct; the adductor ridge is prominent in a variable degree, and is almost confluent with the articular ridge. In one specimen from Beverly Bay, U. S., the scuta were extraordinarily disintegrated, and I could perceive no trace of the external radiating striæ. Tergum, with the basal margin on the carinal side of the spur sometimes deeply (Pl. 5, fig. 4 b), and sometimes only slightly (fig. 4 d), and rarely hardly at all, hollowed out: when much hollowed out the valve may almost be said to be two-pronged, with the carinal prong narrower than the spur. There is no distinct longitudinal furrow, but the whole scutal margin projects above the general surface of the valve. In the carinal margin, in the upper part, there is a remarkable convexity or protuberance in the same plane with the valve, from which it is separated by a very slight and narrow ridge. The spur is about one fourth of the width of the valve, with its lower end abruptly truncated. Internally, the upper surface is much roughened with finely crenated ridges: the distinct crests for the depressores cover the whole of the so-called carinal prong.

Compartments; the radii and alæ have their summits oblique, sometimes a little rounded, but not smooth. The septa on the sutural edges of the radii are remarkably fine, and closely approximate; the denticuli are excessively minute. The sutural edges of the alæ are most delicately crenated; the alæ are largely added to during the diametric growth of the shell, and above the level of the opercular membrane. The parietal pores are square and rather large: they are crossed by transverse septa almost close down to the basis: the longitudinal septa have tolerably large denticuli at their bases. The pores in the basis are crossed by numerous transverse septa. When specimens grow in a group, the basis is sometimes irregularly cup-formed.

Mouth: labrum serrated with small teeth, decreasing in size downwards, on each side of the central notch. Mandibles with the third tooth rather thick and blunt, and with the fourth and fifth knob-like. Maxillæ, with the inferior part projecting much beyond the rest of the edge, and bearing two long single spines: between these two spines and the large upper pair, there are, in a full-sized specimen, about seven pairs of moderately long spines, feathered on their sides. Outer maxillæ thickly clothed with very fine spines, and remarkably prominent.

Cirri: first cirrus, with one ramus having twenty-six segments, and longer by ten segments than the shorter ramus, which has sixteen segments: the shorter ramus, and both ramii of the second pair, have their segments remarkably protuberant in front; the protuberance, in the upper segments, equalling in length the supporting part of each segment: rami of the second cirrus unequal in length by five segments. Third cirrus with the segments only slightly protuberant; rami considerably longer than those of the second cirrus: at the dorsal base of the pedicel of this third cirrus there is no tuft of fine hairs, as is common in many other species. Sixth pair, with the upper segments elongated, bearing from six to seven pairs of spines; dorsal spines short, thin, and few.

Affinities: in external appearance of the shell, this species can hardly be distinguished from some of the white varieties of B. amphitrite; and there is a considerable resemblance, in some of the varieties, in the opercular valves; but the longitudinally striated scuta of B. eburneus suffice to distinguish these certainly very distinct species. Equally, or even more like externally, is this species to the B. Hameri, so that I have received from an eminent naturalist in the United States both species mingled in the same lot, all bearing the same name of B. eburneus; but when the internal structure of the shell is examined, the species are at once seen to be far removed from each other. Still more close is the affinity of this species to B. improvisus, both in internal and external characters: it agrees with this species in the singular habit of being able to live in brackish water: these two species are the only ones which have the labrum serrated with teeth, graduated in size, on each side of the central notch. In the case of young specimens of the var. assimilis of B. improvisus, an inhabitant of the same seas with B. eburneus, the diagnosis is most difficult without long practice; for in the young of eburneus, the compartments are only partially covered by yellow epidermis, and have a striped appearance, the radii are sometimes very oblique, the scuta externally have not acquired their longitudinal striæ, and internally the adductor ridge lies not so close to the articular ridge as it does subsequently; hence I for some time mistook the var. assimilis of B. improvisus for the young of B. eburneus. But I found in the latter, that the rami of the first pair of cirri, are always, even in the earliest youth, more unequal in length, and that each segment of the posterior cirri bears a greater number of pairs of spines, there being, even in very minute specimens, seven pairs. Moreover, after having examined scores of specimens, I found I could almost always distinguish the two species by the smoothness and curvature of the summits of the radii of B. improvisus; I entertain no doubt whatever about the distinctness of the two species; indeed, when both are mature, besides the greater size, striated scuta, &c. of B. eburneus, their general aspect is very different.

22. BALANUS IMPROVISUS. Pl. 6, fig. 1 a-1 c.

Shell white: radii narrow, with their upper margins smooth, slightly arched, very oblique. Tergum with a longitudinal furrow; spur with the end rounded.

Var. assimilis, with longitudinal white hyaline lines.

Hab.--England, Scotland, Belgium (?), Nova Scotia, United States, West Indies, Rio Plata, Southern Patagonia, Guayaquil, West Colombia; attached to wood, shells, rocks, ships' bottoms, from low tidal level to twenty fathoms depth.

General Appearance.--Shell conical, with a rather large diamond-shaped orifice, moderately or but little toothed; very smooth; walls never folded longitudinally; white, with an extremely thin pale-yellow persistent epidermis. The radii are very narrow, with their summits very oblique, rounded, and smooth; the epidermis is generally more persistent on the radii than on other parts, and this is exactly the reverse of what is common with B. eburneus. The specimens from nearly fresh-water in the R. Plata (hereafter to be mentioned), are brownish, and have undergone a remarkable degree of corrosion, the outer lamina of the walls having been entirely removed to near the base; hence the external aspect of these specimens is wholly different from ordinary individuals. The var. assimilis has also a very different appearance, owing to the dead white of the walls being relieved by narrow approximate longitudinal hyaline lines, corresponding with and caused by the longitudinal parietal septa being externally visible through the outer lamina of the parietes; the epidermis on the radii is also of a rather brighter yellow. The largest specimens which I have seen are those from the Plata, and those attached to a ship from the West Indies, and they had a basal diameter of .6 of an inch: from .4 to .5 of an inch is the more usual full average size.

Scuta, with the lines of growth but little prominent: articular ridge prominent, but little reflexed: adductor ridge straight and very prominent, varying a little in its distance from the articular ridge; there is scarcely any depression for the lateral depressor muscle; the upper internal surface of the valve is roughened with ridges. Terga, with a moderately deep longitudinal furrow; spur short, rather narrow, with the end rounded, placed at less than its own width from the basi-scutal angle; in the Rio Plata specimens the spur is close to this angle: the basal margin is generally straight on opposite sides of the spur, but sometimes on the carinal side it is a little hollowed out. The lines of growth are upturned along the carinal margin, which consequently is a little protuberant, but to a varying degree. The crests for the depressores are extremely distinct and prominent. In the varieties having the basi-carinal margin hollowed out, and the carinal margin protuberant, there is a marked resemblance to the peculiar tergum of B. eburneus.

Walls: the parietal pores are tolerably large, and are crossed by numerous transverse septa: the longitudinal septa are very finely denticulated at their bases, but occasionally almost smooth. The radii are, as stated, extremely narrow, and very remarkable from their smooth rounded edges; their septa are barely denticulated. The alæ are remarkably protuberant; they have their summits much less oblique than those of the radii, and sometimes they are almost parallel to the basis: their sutural edges are coarsely crenated. Basis, flat, thin, permeated by pores, but the pores do not generally run to the very centre; they are, as usual, crossed by transverse septa.

Mouth: the labrum is the most remarkable part; on each side of the central notch there are generally two teeth; and on the two sides of the notch itself nine or eleven smaller teeth, decreasing regularly in size downwards till they become so minute as to be hardly visible even under the compound microscope; thus, in the two specimens closely examined, there were altogether twenty-two and twenty-six teeth on the labrum. Mandibles with the two inferior teeth reduced to mere knobs: maxillæ with the lower part of the edge bearing two large spines, and generally, but not always, forming a step-formed projection. Cirri: the ramii of the first pair are but slightly unequal; in one specimen examined there were fifteen segments in one ramus and twelve in the other: segments very protuberant in front. Second cirrus with the segments only slightly protuberant; segments thirteen. Third cirrus longer than the second pair, with the rami rather unequal in length: there is a tuft of long spines on the basal segment of the pedicel of this cirrus. Fourth cirrus twenty-two segments. Sixth cirrus, in the same individual, thirty-four segments: on each of these segments there are five or six pairs of spines. I may specify that the longer ramus of the first cirrus of a large Rio Plata specimen had twenty-four segments.

Varieties, affinities.--When I first met with the var. assimilis, misguided by its general aspect, I did not doubt that it was specifically distinct; I was strengthened in this view by the absolute identity of several hundred specimens attached to two vessels from Jamaica and Trinidad, in the West Indies, with one specimen from Charlestown, in the United States, sent me by Prof. Agassiz, and with several in three lots from the western tropical shores of South America: yet on close examination I can point out no one distinguishing character, either in the shell or animal's body, excepting the longitudinal hyaline lines on parietes, due to the septa being externally visible. The presence of similar lines is variable in white vars. of B. amaryllis and amphitrite, and they are seen in very young specimens of B. eburneus: hence it is impossible to consider so trifling a character as specific; moreover, lately I have seen a British specimen with hyaline lines, and some few other specimens in an intermediate condition. Under the head of B. eburneus, I have stated that although that species and B. improvisus, which in the West Indies are associated together, are most readily discriminated when old, yet when young, they so closely resemble each other that the eye requires much practice to separate them. On account of this species and B. crenatus being sometimes associated together on the shores of England, I have pointed out under B. crenatus, the relative diagnostic characters of the two. The chief affinity of B. improvisus is certainly towards B. eburneus; but in the narrow, oblique, rounded, and smooth-edged radii, there is a relationship shown to the species in the last section of the genus, such as B. amaryllis, and more especially to the fossil B. dolosus: so close is the resemblance in the external appearance of the shell, and in the structure of the opercular valves, to the latter species, that I for some time did not discover their distinctness. Balanus improvisus has hitherto been overlooked by naturalists, and has probably been confounded with B. crenatus or balanoides.

Range and habits.--This species, as far as my experience goes, is commoner on the shores of Kent than on other parts of England: the first specimens which I met with, I owed to the kindness of Mr. Metcalf, they were attached to wooden stakes from Herne Bay, together with a single specimen of B. crenatus: I have seen other specimens from near Woolwich, from the Kentish oyster-beds, from Sandwich, and from Ramsgate. The only other British specimens which I have seen are from the River Itchen, in Hampshire, and from Loch Shieldaig, in Ross-shire (Mus. Jeffreys), from a depth of twenty fathoms. This species is often attached to wood. At Ramsgate, the specimens were attached to a small coasting vessel, and they must have been immersed five or six feet; they were associated with B. crenatus, and with a few of B. balanoides. In the Brit. Mus. there are specimens collected by Mr. Redman, from Nova Scotia, in North America. When her Majesty's ship Beagle was beached at Santa Cruz, in Southern Patagonia, numerous specimens were found adhering to her copper bottom, some so small as to show that the species breeds in those latitudes. Near Monte Video, in the estuary of La Plata, I found many large, but much corroded specimens, adhering to some rocks in a small running stream of perfectly fresh water. The rise of the tide is here small, but at high water the specimens apparently were for a short time covered by the waters of the estuary, here itself only brackish, and occasionally almost fresh. I took home some specimens, and placing them in perfectly fresh water they continued for many hours expanding and retracting their cirri with perfect regularity and vigour. Here then we have a Balanus capable of living in fresh water, and likewise in the saltest seas: even brackish water is a deadly poison to several, probably to most, species of the genus; but this, as we have seen, is not the case with the allied B. eburneus. The water, I may add, at Woolwich, on the Thames, whence I have received B. improvisus, must at times be very brackish. I have already incidentally mentioned that the var. assimilis was attached in great numbers, associated with B. eburneus, tintinnabulum, and amphitrite, on vessels from the West Indies: one specimen sent me by Prof. Agassiz, from Charlestown, was attached to a specimen of B. eburneus; and, lastly, I have seen three sets of the same identical variety attached to shells from Guayaquil (in Mus. Brit. and Cuming), and from West Colombia. Here, then, we have the same species with an enormous range, from Nova Scotia and Great Britain to South Patagonia; and, which is the case with scarcely a single mollusc, it lives both on the eastern and western tropical shores of the South American continent.

23. BALANUS NUBILUS. Pl. 6, fig. 2 a-2 c.

Shell white, rugged: basis in parts imperfectly porose. Scutum with the articular ridge minute; adductor ridge prominent, forming a deep pit for the lateral depressor muscle: tergum with an internal patch of purple; apex produced, purple.

Hab.--California, Mus. Brit. and Aug. Gould; associated with B. glandula, and attached to wood.

I have seen two specimens of this species, brought by Lady K. Douglas from California; and two from Monterey, sent me by Dr. Aug. Gould. This is a very distinct species, coming nearer to B. porcatus than to any other species: it is also allied to B. cariosus. In the basis being in parts solid or not permeated by pores, it has claims to be placed in the next section, in which I at one time included it.

General Appearance.--Shell conical, rugged, sometimes furnished with sharp longitudinal ribs; dirty white. Orifice not large, oval, toothed. Radii rather narrow, with their summits oblique, much jagged. Basal diameter of largest specimen 2.1; height only 1.3 of an inch.

Scuta, broad, with the lines of growth prominent; internally, articular ridge very little prominent, sometimes hardly developed, but thick, ending downwards in a small free point. Adductor ridge prominent, blunt, produced straight downwards, making a deep longitudinal cavity for the lateral depressor muscle; in some specimens this cavity is almost arched over, so as to tend to be tubular, with a short ridge in the middle (Pl. 6, fig. 2 a): in other specimens there is no trace of this tubular structure. Terga, with the apex beaked, beak triangular, dull purple; the longitudinal furrow is so shallow as hardly to exist. The basal margin slopes down on both sides, with a nearly equable curvature towards the spur; hence the spur is broad in its upper part, and narrow at its obliquely truncated lower end. Internally, there is an elongated dark purple patch: the shallow articular furrow is of quite remarkable breadth; the articular ridge is medial, and the inflected scutal margin is not wide. The internal surface of the spur is formed into a ridge, which runs a little way up the valve, and is sometimes partially separated from the spur itself (fig. 2 c), making the basal extremity toothed or double. The crests for the depressores are pretty well developed.

Walls, moderately strong: inner lamina slightly ribbed: the denticuli on the bases of the parietal longitudinal septa are sharp: I could not see any transverse septa in the parietal tubes. The radii are rather narrow; their summits are remarkably jagged and very oblique; the septa are plainly denticulated on both sides, but chiefly on the lower side; each septum itself, towards the inner lamina of the radius, branches and divides: the interspaces are filled up nearly solidly. The alæ have apparently their summits less oblique than those of the radii: their sutural edges are finely crenated. The lower edge of the sheath is hollow underneath. The basis is flat; it is rather thin, and imperfectly porose; in parts it is not at all porose, in others it is traversed only by very minute pores: there is nevertheless, in some parts, even where the upper layer is not porose, an underlying, cancellated layer.

Animal's body unknown.

24. BALANUS CORRUGATUS. Pl. 6, fig. 3 a, 3 b.

Shell white, longitudinally folded; radii narrow. Scutum internally without an adductor ridge.

Fossil, Sub-Appennine formations; Colle in Tuscany; Mus. Greenough.

I have seen only two specimens of this species attached to rock, collected by Mr. Greenough, at Colle, and kindly given by him to me. The species comes near to the living B. crenatus, also found fossil in deposits of this same age; it differs, however, distinctly from that species, in having its basis permeated by pores, and, in a less degree, in the sutural edges of the radii being more plainly crenated: the opercular valves of the two species closely resemble each other. This may be the B. stellaris of Bronn, but it is futile attempting to identify the species of this genus merely by external characters, even when aided, as in this case, by an excellent drawing of the shell.

General Appearance.--Shell conical, with broad rounded longitudinal folds; orifice of moderate size, oval; radii narrow, with their upper margins oblique; but the summits of both specimens had been much broken. Colour, as it appears, originally white. Basal diameter of largest specimen 3/4 of an inch.

Scuta, with the upper portion much reflexed; the articular ridge is very prominent, and the articular furrow of great width; when the valve is viewed from the outside the articular ridge is very conspicuous: there is no adductor ridge. Terga, with the longitudinal furrow very slight; the spur is from one third to one fourth of the width of the valve, and its basal end is blunt and almost truncated; it stands about half its own width from the basi-scutal angle. Internally, the articular ridge is very prominent, and the articular furrow narrow and deep, extending down the valve in the line of the spur.

Parietes: the parietal tubes are remarkably large, and I think this can hardly be an individual peculiarity: the tubes are crossed by many transverse septa, close down to the basis. The radii are narrow, and have jagged, oblique summits: their sutural edges have very distinct septa, barely denticulated, with the interspaces filled up solidly. The alæ have oblique summits; I was unable to make out the structure of their sutural edges. The Basis is very distinctly permeated by pores, which are crossed by transverse septa.

The shell and opercular valves of B. corrugatus so closely resemble the same parts in B. crenatus, that I should not be much surprised at seeing the two species graduating into each other, if a larger series of specimens, from beds intermediate in age between the Sub-Appennine formations and the present time, were obtained. If indeed the basis of B. crenatus were permeated by pores, the two species could hardly be discriminated.

Section D.

Parietes permeated by pores. Basis and Radii not permeated by pores.

25. BALANUS PORCATUS. Pl. 6, fig. 4 a-4 e.

BALANUS PORCATUS. Emanuel da Costa. Hist. Nat. Test. Brit., p. 249 (1778).

LEPAS BALANUS. Linn. Syst. Naturæ (1767).

---- ---- Born. Testacea Mus. Cæs. Desc., Tab. 1, fig. 4, (1780).

---- ---- Chemnitz. Syst. Conch., 8 Band., Tab. 97, fig. 820, (1785).

BALANUS ARCTICA PATELLIFORMIS. Ellis. Philosoph. Transact., vol. 50, Tab. 34, fig. 18 (1758).

---- SULCATUS. Bruguière. Encyclop. Method., Tab. 164, fig. 1 (1789).

LEPAS COSTATA and BALANUS. Donovan. British Shells, 1802-1804, Tab. 30, fig. 1, 2.

LEPAS SCOTICA. W. Wood. General Conchology, Pl. 6, fig. 3, sed non Lepas balanus, Pl. 7, fig. 3, (1815).

BALANUS ANGULOSUS. Lamarck (1818), in Chenu, Illust. Conch., Tab. 11, fig. 11.

---- TESSELATUS. Sowerby (!). Mineral Conchology, Tab. 84 (1818).

---- SCOTICUS. Brown. Illust. Conch. Great Britain, Pl. 7, fig. 2, sed non, Pl. 6, fig. 9 et 10 (1827); 2d edit., Pl. 53, fig. 1-3, 22, 23 et Pl. 54, fig. 1-3.

---- GENICULATUS. Conrad. Journal Acad. Philadelphia, vol. 6, part 2, p. 265 (1830), Tab. 11, fig. 16.

---- ---- Aug. Gould (!). Report on the Invertebrata of Massachussetts, fig. 9 (1841).

Shell white, generally sharply ribbed longitudinally: radii with their summits almost parallel to the basis. Scutum longitudinally striated: tergum with the apex produced and purple.

Var. (a): Walls without longitudinal ribs. Mus. Brit., Cuming, Stutchbury, Jeffreys.

Hab.--South shores of England, Ireland, Scotland, Shetland Islands, Iceland, Davis's Straits, 66° 30′ N.; Lancaster Sound, 74° 48′ N. (Mr. Sutherland). Maine and Massachussetts, United States. China (?). In deep water, common on shells, crustacea, and rocks, sometimes imbedded in sponges.

Fossil in the glacial deposits of Scotland, Uddevalla, and Canada; in the mammaliferous and Red Crag of England; Mus. Lyell, Sowerby, S. Wood, &c.

General Appearance.--Shell conical, somewhat convex; white, sometimes tinted yellowish, from the thin investing membrane; the produced tips of the terga are purple: the parietes of each compartment have from two to four strong, prominent, sharp, straight longitudinal ribs; these are sometimes irregular, and rarely, as will presently be described, they are absent. The radii are smooth and of considerable breadth; their summits are nearly parallel to the basis or only slightly oblique: hence the orifice is entire; it is rather small and ovate, being broad at the rostral end, and very sharp and narrow at the carinal end.

Dimensions.--The largest specimens which I have seen from Great Britain or Ireland, have been 1.3 of an inch in basal diameter: in Mr. Cuming's collection, however, there was one much depressed specimen from the Shetland Islands, 2.1 in basal diameter: a regularly conical specimen from the coast of Massachussetts attained a nearly equal diameter; out of the glacial deposits in the Isle of Bute, Scotland, several specimens had this same diameter, namely, two inches, and were even more steeply conical, being 1.85 in height; some glacial specimens from Uddevalla and Canada, in Sir C. Lyell's collection, were 1.7 in basal diameter. Hence, it appears, as we shall presently see is likewise the case with B. crenatus and Hameri, that northern specimens, and those from the United States and from the glacial deposits, often exceed in dimensions those from Great Britain or Ireland.

Scutum: the lines or ridges of growth are broad and prominent; they are divided into square beads by fine striæ, radiating from the apex: and hence the valve is longitudinally striated. Internally, the articular ridge is extremely little prominent; the adductor ridge, or what must be called such, runs straight down under the articular ridge, making a deep longitudinal pit for the lateral depressor muscle. Tergum: the apex is a little produced, and coloured purple, as well as the upper internal surface of the valve; there is no longitudinal furrow, only a very slight depression: the spur is placed close to the basi-scutal angle; it is rather long, and measured across the upper part, is half as wide as the valve: its lower end is truncated and rounded; the basal margin slopes towards it. Internally, a very small portion of the scutal margin is inflected: the articular furrow is shallow and broad: the crests for the depressores are feeble. In young specimens the spur is bluntly pointed.

The Parietes (4 e) have large square parietal tubes: in the upper part these are filled up solidly without transverse septa: the longitudinal septa are finely denticulated at their bases, and the denticuli extend unusually close to the outer lamina. In very young specimens the inner lamina of the parietes is ribbed, in lines corresponding with the longitudinal septa, as is the case with most species of the genus; but in medium and large-sized specimens, there are between the ribs, thus produced, from one to four smaller ribs, which do not correspond with any longitudinal septa; they are finely denticulated at their bases, and may be considered as the representatives of longitudinal septa which have not been developed and reached the outer lamina. I have seen no other instance of this structure, namely, the presence of a greater number of ribs, on the inner lamina of the walls, than there are longitudinal septa. The radii have their summits generally parallel to the surface of attachment, as is usual in the first section of the genus, but sometimes they are slightly oblique: the septa sometimes rudely branch a little, but they exhibit scarcely a trace of denticuli: the interspaces are filled up quite solidly. The alæ have their summits very oblique; their sutural edges are finely crenated.

Basis, rather thin, translucent, not permeated by pores; obscurely furrowed in lines radiating from the centre: the circumference is marked in a peculiar manner by the longitudinal septa, and by the tips of those intermediate, denticulated ribs, which occur on the inner lamina of the parietes.

Mouth: labrum with six teeth: mandibles with the fourth and fifth teeth small and rudimentary: maxillæ, with a small notch under the upper pair of spines; in the lower part there is a single large spine. Cirri, dark brownish purple, making a singular contrast with the white operculum and shell; first pair, with one ramus, having twenty-six segments, and about twice as long as the shorter ramus, having twelve or thirteen segments, with their front surfaces protuberant. In the second pair the segments are but little protuberant: third pair about one third longer than the second pair: sixth pair, elongated, having in the same individual forty-six segments; these segments have shield-shaped fronts, bearing five pairs of spines, with some minute intermediate bristles. There is the usual point at the dorsal base of the penis.

Range: Geological History.--This species is common on the shores of Scotland and Ireland; the most southern point of Europe whence I have happened to see a specimen is Tenby, in South Wales: but I have no doubt it is found further south; and Mr. Jeffreys, who knows this species well, has found it common on the extreme southern shores of England. In the United States, it is found on the shores of Maine and Massachussetts: northward, I have seen specimens from Iceland, from Davis's Straits, and from Lancaster Sound, in lat. 74° 48′ north; these latter I owe to Sir J. Richardson. It is an inhabitant of deep water; in Mr. Thompson's collection there are several specimens from the Bay of Belfast, marked twenty-five fathoms, and one group said to have come from "about fifty fathoms, on the coast of Antrim:" one specimen from Cape St. Anne, Massachussetts, is marked as having come from only five fathoms. This species is commonly associated, on both sides of the Atlantic, with B. crenatus, and sometimes with B. Hameri and Verruca Strömia: mollusca, such as pectens, modioli, and oysters, offer the most usual surfaces of attachment: I have, however, seen many specimens on crustaceans, on rocks, and even on the roots of the larger sea-weeds. This species is very common in the glacial deposits of Uddevalla, of Skien in Norway, and of Canada, and is associated with the same species as in the living state: I have seen, also, specimens from the same formation in the Island of Bute, Scotland. I have seen numerous specimens from the mammaliferous crag, and a few from the Red Crag of England. I owe to the kindness of Mr. J. de C. Sowerby an inspection of the original specimens of the B. tesselatus of the Mineral Conchology, which is certainly the present species.

Affinities.--This species is very distinct from every other; it comes nearest, as shown in all the characters derived from its opercular valves, to B. nubilus, and in this latter species we have seen the basis plainly tending to lose its pores and thus become solid. B. porcatus is perhaps allied in some degree to B. trigonus, and slightly to B. crenatus. The rather broad radii, with their summits hardly oblique, give this species a very different aspect from those species of the genus amongst which it must be placed.

Varieties.--A conical specimen, sent to me from the coast of Massachussetts, is remarkable from the radii not having been at all developed, being represented by mere fissures. I have seen a few specimens of var. (a), (one collected by Sir E. Parry in the arctic seas) which had a remarkably different aspect from the common forms, but which, after a careful examination of the opercular valves and of the animal's body, I feel convinced are not specifically distinct: they are characterised by the walls being smooth and absolutely destitute of the external longitudinal ribs; by the shell being more cylindrical, with broader radii, and with the orifice larger and more rhomboidal; the walls and radii are much thinner, and the internal lamina is less plainly ribbed: the beak of the tergum is not purple. As most of these specimens had grown in a group crowded together, the difference of shape, and perhaps the thinness of the walls, is thus explained. In a specimen from Davis's Straits, in Mr. A. Hancock's collection, most of the above characters are in an intermediate condition; there are only a few external longitudinal ribs on the parietes; and the terga have not purple apices. In Mr. Cuming's collection there are some fine, brilliantly white specimens (without opercula) from the coast of China; these have thin walls and radii, and the walls are not longitudinally ribbed, but they are not smooth: the orifice is not large, nor the shape of the whole shell cylindrical. It is just possible that these latter specimens may be a distinct and representative species, but I do not think so.

26. BALANUS PATELLARIS. Pl. 6, fig. 5 a-5 c.

LEPAS PATELLARIS, (Gmelin). Spengler. Schriften der Berlin. Gesellschaft, &c. b. i (1780), Tab. 5; Chemnitz, Neues Syst. Couch., Tab. 98, fig. 839.

Shell depressed; brown, generally with obscure longitudinal violet stripes: radii (in full-grown specimens) with their summits rounded and surfaces finely ribbed parallel to the basis: basis sometimes permeated by imperfect pores. Scutum internally with an adductor ridge.

Hab.--Bengal, on wood, Mus. Brit.; on a shell, Mus. Stutchbury; Philippine Archipelago (young specimen), Mus. Cuming. According to Spengler, on the Coromandel and Malabar coasts.

General Appearance.--Shell depressed, sometimes much depressed: orifice elongated, rhomboidal, but little toothed; surface smooth, but in old specimens sometimes with the walls slightly folded longitudinally. The radii are rather narrow, with their summits oblique; in old specimens their summits are rounded, and their whole surface finely ribbed parallel to the basis. Colour, in old specimens dirty brown, tinged with violet, sometimes in longitudinal bands, and with whiter irregular marks in the upper parts owing to disintegration: in young specimens the walls are regularly banded longitudinally, with violet-brown and dirty white; the radii being generally of a paler dirty red or violet. Basal diameter of largest specimen .9 of an inch.

Scuta, externally rather smooth; internally, articular ridge prominent, reflexed, with the lower edge hollowed out so as to be slightly hook-formed: adductor ridge small; there is a slight pit for the lateral depressor. Tergum, with the spur bluntly pointed, placed at about its own width from the basi-scutal angle; there is no longitudinal furrow, only a slight depression; carinal margin arched and protuberant: internally, articular ridge extremely prominent, running down in the direction of the middle of the spur: crests for the tergal depressores well developed.

Parietes, with the pores rather large; the internal lamina is very strongly ribbed, the ribs being but slightly denticulated at their bases: the parietal pores do not appear to be crossed by transverse septa: sheath closely attached to the walls. The radii have jagged oblique summits forming an angle of about 45° with the horizon; in old specimens they become more oblique and narrow: and are then very remarkable from their summits being arched and rounded, with a crenated edge, and with their whole surface transversely ribbed in horizontal lines; this is likewise the case with the recipient furrow in the opposed compartments: in young specimens the radii are externally quite smooth: the septa on the sutural edges are bluntly denticulated; the interspaces being filled up solidly. The alæ have their summits oblique, but much less oblique than the summits of the radii; their sutural edges are very finely crenated.

Basis thin, either quite solid, that is, not permeated by pores, but only furrowed in lines radiating from the centre, or permeated by pores towards the circumference, the pores being of very small diameter;--so that we here have an important character variable within the limits of the same species. Base flat, and this holds good, as remarked by Spengler, even when the specimens are attached to cylindrical pieces of wood.

Animal's body unknown.

Affinities.--In the basis being sometimes permeated towards the circumference by pores, and by the colouring (the other species in this and the next section being dirty white), B. patellaris has almost as strong a claim to be ranked in the last as in the present section: in the rounded summits of the radii, and in the state of the basis, it, perhaps, shows more affinity to B. improvisus than to any other species; it is, however, almost equally allied to B. glandula.

27. BALANUS CRENATUS. Pl. 6, fig. 6 a-6 g.

B. CRENATUS. Bruguière. Encyclop. Method. (des Vers) 1789.

LEPAS FOLIACEA, var. a. Spengler. Skrifter af Naturhist. Selskabet, b. i, 1790.

---- BOREALIS. Donovan. British Shells, Pl. 160 (1802-1804).

B. RUGOSUS. Pulteney (?) Catalogue of Shells of Dorsetshire, 1799.

---- ---- Montagu (?) Test. Brit. 1803.

---- ---- Gould (!). Report on Invertebrata of Massachussetts (1841), fig. 10.

B. GLACIALIS (?) J. E. Gray. Suppl. Parry's Voyage, 1819.

B. ELONGATUS (!), CLAVATUS (!), Auctorum variorum.

Shell white: radii with their oblique summits rough and straight. Scutum without an adductor ridge: tergum with the spur rounded.

Hab.--Great Britain, Scandinavia, Arctic Regions as far as Lancaster Sound, in 74° 48′ N. (Mr Sutherland); Behring's Straits (Captain Kellett); United States; Mediterranean; West Indies, (Mus. Brit.); Cape of Good Hope, (Mus. Krauss). Generally attached to shells and crustacea in deep water; sometimes to ships' bottoms. Very common.

Fossil in glacial deposits of Scandinavia and Canada, Mus. Lyell; in the mammaliferous, and Red, and Coralline Crags, Mus. S. Wood, J. de C. Sowerby, Bowerbank; Miocene formation, Germany, Mus. Krantz.

I find, in most collections, this species confounded with B. balanoides; I have even seen the two species, placed by Leach, on the same tablet in the British Museum: B. balanoides is, moreover, generally confounded with Chthamalus stellatus; nor has any one hitherto separated the present species from B. improvisus. On the other hand, trifling varieties, both of B. balanoides and B. crenatus, have commonly been considered as specifically distinct. From these facts it will be seen in what confusion our commonest British species of Balanus have been left. After due deliberation, I have little doubt that this is the B. crenatus of Bruguière, and probably the B. rugosus of Montagu, but this latter author omits all reference to the really important diagnostic characters between this species and B. balanoides. The B. crenatus is certainly the B. rugosus of Dr. Aug. Gould. In various collections, I find specimens of B. crenatus, when coming from the arctic regions, called B. glacialis, arcticus, and borealis; though I have not met with an authentic specimen of the B. glacialis of Gray ('Supp. Parry's Voyage,' 1819, p. ccxlvi), I have little doubt that it would prove to be the present species.

General Appearance.--White, usually of a dirty tint, from the yellowish or brownish persistent epidermis: conical, generally (fig. 6 a) with the parietes rugged and irregularly folded longitudinally; but sometimes much depressed and extremely smooth (6 b); often cylindrical and very rugged; occasionally club-shaped (6 c), the upper part being much wider than the lower: specimens in this latter condition sometimes have extremely narrow parietes, like mere ribs, and wide radii. The orifice in the cylindrical varieties is often most deeply toothed. The radii are generally narrow, and have jagged oblique summits; but not infrequently they are so narrow as to form mere linear borders to the compartments. The orifice is rhomboidal, passing into oval, either very deeply or very slightly toothed.

Dimensions.--The largest British specimen which I have seen was only .55 of an inch in basal diameter: specimens from Greenland and the northern United States frequently attain a diameter of three-quarters of an inch, and I have seen one single somewhat distorted specimen actually 1.6 of an inch in basal diameter. The specimens from the glacial deposits of Uddevalla and Canada appear, on an average, to attain as large or larger dimensions than those from the United States: on the other hand, the specimens from the mammaliferous and Red Crag are smaller, the largest being only .35 in basal diameter. When individuals have grown crowded together, their length is often twice, and even occasionally thrice, as great as their greatest diameter; thus I have seen a Greenland specimen 1.6 of an inch in length, and only .75 in diameter. In the British Museum there are some arctic specimens, one and a half inch in length, only half an inch in diameter at the summit (fig. 6 c), thence tapering downwards to a blunt point.

Scuta; the lines of growth are but little prominent: the surface is generally covered by disintegrating membrane. The upper ends are usually a little reflexed, so that the tips project freely as small flattened points. Internally, the articular ridge is highly prominent and somewhat reflexed: there is no adductor ridge, but a very distinct impression for the adductor muscle: the depression for the lateral depressor muscle is small, but variable. The terga are rather small: the spur is short, and placed at rather less than its own width from the basi-scutal angle; the basal margin slopes a little towards the spur, of which the lower end is rounded or bluntly pointed in a variable degree. There is no longitudinal furrow, hardly even a depression. Internally, the articular ridge is very prominent in the upper part; the crests for the tergal depressores are well developed, but variable.

Compartments.--The internal carinal margin of each compartment, from the sheath to the basis, generally, but not invariably, projects a little inwards beyond the general internal surface of the shell, in a manner not common with the other species of the genus: the basal edge of this projecting margin rests on the calcareous basis, and is crenated like the basal edges of the longitudinal parietal septa. The whole internal surface of the shell is ribbed, but the ribs are not very prominent. The parietal tubes are large, and are crossed in the upper part, and often low down, by transverse thin septa: the longitudinal parietal septa are only slightly denticulated at their bases; occasionally they divide at the basis close to the outer lamina of the parietes, making some short outer subordinate pores. In the circular furrow beneath the lower edge of the sheath, there are sometimes little ridges, dividing it into small cells: sometimes, however, this furrow is filled up by irregular knobs of calcareous matter. The radii are always rather narrow, and often they form mere linear ribbons of nearly uniform width along the edges of the compartments. Their summits or edges are always more or less irregular and jagged: they form an angle with the horizon of generally above 40°. Their septa are fine, and barely or not at all denticulated. The alæ have oblique summits: their sutural edges are rather thick and distinctly crenated. Basis flat, calcareous, very thin, with the surface slightly marked by radiating furrows, which furrows answer to the radiating pores that occur in the bases of most species. In a club-shaped arctic specimen, one inch and a half in length, the summit being half an inch and the base only one fifth of an inch in diameter, the basis was still calcareous, thick, and not permeated by pores.

Mouth: labrum with six teeth: mandibles with the fourth tooth minute or rudimentary, and the fifth generally confluent with the inferior angle. Maxillæ with generally, but not invariably, a small notch under the upper pair of great spines. Cirri, first pair with the rami very unequal in length, one ramus being nearly twice the length of the other; in a large specimen having a cylindrical shell the proportional numbers of the segments in the two rami of the first cirrus were ten to twenty-three; in a small conical specimen the numbers were only eight to thirteen. The second cirrus has only two or three more segments than the shorter ramus of the first pair: the third cirrus has one or two more segments than the second; but it is nevertheless decidedly longer than the second. On the dorsal surfaces of both segments of the pedicel of the third cirrus, there is a tuft of fine spines. The segments of these three pairs of cirri are not much protuberant in front. The segments of the posterior cirri have, each, four, or five, or six pairs of spines. Penis, with a straight, sharp, short point on the dorsal basis.

Range, habits, &c.--I have received specimens from all parts of the coast of Great Britain and Ireland, generally attached to crustacea and mollusca, and never hitherto from rocks uncovered by the tide. This species is also attached to floating timber, sticks, fuci, and occasionally to pebbles at the bottom of the sea. Mr. Thompson has sent me specimens from twenty-five fathoms depth in Belfast Bay: others on a Pinna from about fifty fathoms on the coast of Antrim; others from between three and six fathoms attached to Laminaria digitata: there is a specimen in Mr. Jeffreys' collection marked forty-five fathoms. It is often associated, both on the coasts of America and Britain, with B. porcatus, and though these species are so distinct, yet when both have their surfaces similarly affected by being attached, as is often the case, to large Pectens, it is not at first easy, by external characters, to distinguish them, except by close inspection of the terga, which in B. porcatus are beaked and purple. The B. crenatus is sometimes associated in deep water with B. Hameri. At Ramsgate, in Kent, I saw a rudder of a ship, in which the two or three upper feet were thickly coated with B. balanoides, and the two or three lower feet with B. crenatus and improvisus mingled, together with a few of B. balanoides: occasionally vessels are thickly encrusted with this species, but I have never seen an instance of its concurrence with B. tintinnabulum and amphitrite--the commonest species on ships coming from the south. I have seen specimens from Greenland, Baffin's Bay, the coast of Labrador, and other specimens marked simply, "Arctic regions," and, again, others from the shores of Maine and Massachussetts. The arctic specimens, and those from the northern United States, are larger than the British. I have seen one single minute specimen on a crab, marked as having come from the Mediterranean. In the British Museum, amongst some specimens of B. eburneus, ticketed as having been sent from Jamaica, there was a small group of specimens, differing in no one essential respect from the common varieties of B. crenatus: at first I concluded that this was an erroneous habitat, and that the specimens had really come from the United States, where B. eburneus, is found as well as in the West Indies: for it appeared to me exceedingly improbable that an animal which can exist in lat. 75° N. should inhabit the hot shores of Jamaica: but subsequently I have received a specimen from Prof. Krauss, collected by himself in Algoa Bay, which is perfectly characterised, and even has the little cells in the furrow under the sheath: so that I am compelled to admit this enormous range and capability of resisting the most extreme climates. That this species should live in the tropical seas is the more surprising, as the large size of the specimens in the northern seas and in the glacial deposits, might fairly have been supposed to have indicated special adaptation for a cold climate. The great geographical range of this species accords with its range in time from the present day to the Coralline Crag period.

The specimens from the glacial deposits which I have examined, chiefly in Sir C. Lyell's collection, are very fine and large; they are often associated, like the now living individuals, with B. porcatus and Hameri: they come from the well-known formation of Uddevalla and from Canada. There are well-characterised specimens in the mammaliferous Crag, at Bramerton and near Norwich, in Sir C. Lyell's collection, and from Sutton and other places in the Red Crag of the eastern shores of England: these specimens are decidedly not only smaller than the glacial, but than the recent English specimens; for the largest Crag specimens which I have seen had a basal diameter of only .35 of an inch. The specimens which I have seen from the Coralline Crag, and some others sent me by Krantz from the miocene formation of Flonheim bei Abzei, in Germany, had not their opercular valves, yet I cannot doubt, considering how few species there are in the present section of the genus, that I have rightly identified them.

Diagnosis.--Under the head of B. balanoides I shall make a few remarks on the diagnosis between that and the present species; as B. improvisus is found on the British shores, sometimes mingled with B. crenatus, I may observe that, externally, the only difference consists in the edges of the radii in B. improvisus being much smoother and rounded, and in the whole shell being less rugged. Internally, in B. improvisus the porose basis, the presence of an adductor ridge on the under side of the scutum, the graduated teeth on each side of the central notch in the labrum, and the little inequality in length of the rami of the first pair of cirri, are clearly and amply diagnostic.

28. BALANUS GLANDULA. Pl. 7, fig. 1 a, 1 b.

Shell white; parietes with the internal lamina generally strongly ribbed longitudinally, with the pores imperfect and small, sometimes in part absent; radii narrow, with their summits rounded. Scutum with an adductor ridge; tergum with the spur truncated and rounded.

Habitat.--California, Mus. Cuming, Aug. Gould; attached to shells and wood, together with B. nubilus. Southern Pacific ocean, attached to Pollicipes polymerus; Mus. Brit.

General Appearance.--Shell steeply conical, or cylindrical and elongated; dirty white; walls rugged, longitudinally folded; radii narrow, with their summits very oblique and rounded; orifice toothed. Basal diameter of largest specimen half an inch.

Scutum, resembling externally that of B. crenatus; rather broad, surface smooth; articular ridge very prominent, and articular furrow very wide; hence, when the summits of the opercular valves are worn down, the two scuta together form a square projection indenting the two terga, as in B. balanoides. Internally, there is a small adductor ridge, on the lower side of which there is a pit, as if for a muscle. The depression for the lateral depressor muscle is small, but variable. Tergum without any longitudinal furrow, and hardly a depression: spur broad, with its lower end truncated and rounded; internally, articular ridge very prominent; crests for the depressores well developed.

Compartments:--The internal surface of the parietes is smooth in the upper part beneath the sheath, but generally very strongly ribbed in the lower part, the ribs being plainly denticulated at their bases; in other specimens, the ribs are very small, and even in parts quite obsolete. The parietal pores are short and imperfect, sometimes reduced to an extremely minute size, to be detected only when the walls are broken across near the basal edge, and most carefully examined; occasionally not even a trace of a pore exists. Hence in this respect, this species offers a singular case of variation. The radii are narrow, and of nearly the same width from top to bottom; their very oblique summits, when well preserved, are smooth and rounded; their sutural edges are ribbed or crenated with extremely fine, smooth septa; the recipient furrow is plainly marked by these septa. The sutural edges of the alæ are crenated; their summits are less oblique than those of the radii.

Basis, thin, finely furrowed in lines radiating from the centre; margin sometimes deeply sinuous.

Mouth: labrum with the central notch rather widely open, with four teeth on each side of it: palpi with very short spines along their inner margins: mandibles with the fourth and fifth teeth forming mere knobs: maxillæ small, with a mere trace of a notch under the two great upper spines. Cirri; first pair with the rami unequal by three or four segments, the longer ramus being only one quarter of its own length longer than the other ramus. Second pair short, with the segments (and those of the shorter ramus of first pair) somewhat protuberant. Third pair with the rami one third longer than those of the second pair. Sixth pair with the upper segments elongated, and bearing six or seven pairs of spines.

Affinities.--This species in general appearance closely approaches B. crenatus and balanoides, and it is related to them in many essential parts, such as in the opercular valves. It agrees with B. balanoides, and differs from B. crenatus, in the smallness and imperfection of the parietal pores, and in the radii having rounded summits; it agrees with B. crenatus in the structure of its basis, and in the prominent longitudinal ribs on the internal surface of the parietes, and differs from that species in the spur of the tergum being squarer, and in the scutum having an adductor ridge.

Range.--From the appearance of the Californian specimens, I suspect that they had adhered to tidal shells and to wood. The specimens in the British Museum, adhering to Pollicipes polymerus, consist of two lots, one of unknown origin, and the other certainly brought from the southern half of the Pacific Ocean by Sir James Ross: it deserves notice, that the Pollicipes polymerus, the supporting object, ranges from California to the southern Pacific Ocean.

Section E.

Basis membranous.

29. BALANUS BALANOIDES. Pl. 7, fig. 2 a-2 d.

LEPAS BALANOIDES. Linn. Fauna Succica, 1746, et Syst. Naturæ, 1767.

---- ---- O. Fabricius. Fauna Groen., p. 424, 1780.

---- ---- ET CLIVATUS. Montagu (!). Test. Brit., 1803.

BALANUS VULGARIS (?) Da Costa. Hist. Nat. Testacea, Pl. 17, fig. 7, 1778.

---- OVULARIS ET ELONGATUS. Aug. Gould (!). Report, Invertebrata of Massachussetts, figs. 7 and 8, (1841).

---- PUNCTATUS, CYLINDRICUS, ELONGATUS, FISTULOSUS CLAVATUS. Auctorum variorum. Sed non B. punctatus, Bruguière, Encyclop. Method., et non B. punctatus, Montagu, Test. Brit.

Parietes either solid, or cancellated, or rarely formed by a single row of pores. Tergum, with the spur bluntly or sharply pointed.

Var. (a) with the parietes permeated by tubes; spur of tergum sharply pointed; segments in the posterior pairs of cirri, bearing from eight to ten pairs of spines.

Habitat.--Great Britain, France, Norway, Shetland Islands; Greenland, according to O. Fabricius; North America, in lat. 66° 34′ N.; Labrador; Nova Scotia; Massachussetts, Delaware. Extremely common, attached to rocks, shells, and wood, within the tidal limits.

I have no doubt that the present species is the Lepas balanoides of Linnæus; though O. Fabricius is the only author who gives, in his "Fauna Groenlandica," a sufficient description for the species to be recognised with certainty. I believe this also is the B. balanoides of Bruguière, though he is in error, as far as my experience goes, in stating that the basis is ever calcareous. I have little doubt, also, that this is the B. vulgaris of Da Costa. The B. balanoides, in its corroded and therefore punctured state, is certainly the B. punctatus of most British collections; but I do not believe it is the B. punctatus of Montagu, which I have scarcely any doubt is the Chthamalus stellatus, so often found in the southern shores of England, and even in some of the best arranged collections, mingled with our present species.

General Appearance.--The shell, in middle-sized and old specimens, is almost invariably folded longitudinally and irregularly; it is either dirty white or very often pale brown, and punctured from the outer lamina having been corroded, to which action it is extremely subject. In very young specimens, the surface is usually quite white and smooth. The shell is sometimes much depressed; generally conical, but when crowded together, cylindrical or club-shaped, one specimen being even more than five-and-a-half times as long as wide. In Mr. Jeffreys' collection there is a specimen 2.5 of an inch long, .45 in diameter at the summit, only .2 in the middle, and rather more than .2 near the base. Another specimen was 1.8 in length, its greatest diameter being .35 of an inch at the summit. On the other hand, I have seen a very depressed variety, with deeply folded walls, in Mr. Thompson's collection from near Dublin, which was no less than four times as wide as high; so that the difference in proportion of height and greatest width, in the two extreme specimens, was nearly as 10 to 1. Occasionally, from some unknown cause, isolated specimens become cylindrical. The orifice of the shell, in the much elongated specimens, is generally deeply toothed. The radii are always narrow, sometimes extremely narrow, and have their summits smooth and rounded.

English specimens do not usually attain half an inch in basal diameter; I have, however, seen one from near Yarmouth .9 of an inch in diameter. Specimens from Massachussetts seem rather larger than the average size of British specimens, many being .6 of an inch, and one specimen a whole inch in basal diameter.

The opercular valves so closely resemble those of B. crenatus, that the description is necessarily comparative; in some cases they could hardly be discriminated; generally, owing to the disintegration to which this species is subject, the tips of the scuta are worn off, and hence the articular ridges together form (Pl. 7, fig. 2 a) a square projection, indenting the two terga; but I have examined young specimens and others when not disintegrated, in which the opercular valves, viewed externally, presented no difference whatever from those of B. crenatus. The scuta, however, are, I think, generally rather thicker, with the growth-ridges more prominent, and with the tips certainly less reflexed than is usual with B. crenatus. Internally, the articular ridge is rather less prominent: there is no distinct adductor ridge. The terga are often rather narrower in proportion, and this especially holds good in the elongated varieties; in these latter, there is occasionally a moderately deep longitudinal furrow: the spur is often exactly the same shape as in B. crenatus, but it is apt to be rather longer (Pl. 7, fig. 2 c) and more pointed: in var. (a) it is pointed (fig. 2 d) in a very remarkable manner. Internally, the articular ridge is decidedly more prominent than in B. crenatus; the crests for the tergal depressor muscles are either well developed or almost absent. From this description it will be seen, how singularly the opercular valves of the common varieties of these two species resemble each other. I may mention that in some of the much elongated specimens, the muscles going to the opercular valves partially lose their transverse striæ, and become ligamentous.

The Parietes are either quite solid, or more commonly are permeated by minute pores, or by small irregular square tubes (Pl. 7, fig. 2 b), which only run up each successive zone of growth, for very short distances, giving to the shell a cancellated structure, which from corrosion is often externally visible. In the rather rare variety (a) the parietes are permeated by regular tubes, extending up to the apices of the compartments, but crossed by transverse septa. The longitudinal septa, when such can be said to occur, in no case are denticulated at their bases. The internal surface of the parietes is either quite smooth or is traversed (Pl. 7, fig. 2 b) by very slight anastomosing ridges, but never, even in var. (a), by regular longitudinal ribs, as in most other species. The carinal margin of each compartment, on the inside, projects, as in B. crenatus, inwards, beyond the general surface of the shell, and running down, rests on the basal membrane. The lower edge of the sheath is rarely hollow beneath. The walls are lined by purplish, or pale brown, or sometimes by almost black corium; numerous tubuli penetrate the under sides of the walls and opercular valves; and it is the intersection of these tubuli that gives the punctured appearance to the often corroded surface of the shell. The radii are narrow, generally very narrow; they have their upper and outer margins, as seen externally, very oblique, rounded and (when well preserved) smooth; their sutural edges are either quite smooth, or sometimes just perceptibly pitted, like the basal margin of the walls, or occasionally furnished with globular or arborescent little ridges. The alæ are also very oblique, but to a variable degree, sometimes only slightly oblique: their sutural edges are either smooth or obscurely crenated. Basis, membranous; in some much elongated specimens, during continued growth, the basal edges of the compartments approach each other so closely as almost to touch, so that the whole shell becomes pointed at the bottom; but on careful inspection I have never failed to find, even in the most pointed specimens, a minute basal membrane; in other much elongated varieties, in which the shell has apparently become too large for the animal's body, the basal membrane, instead of being flat, becomes drawn up deeply inwards, so as to touch the surface of attachment only close round the basal edges of the shell.

Mouth: labrum with the teeth on each side of the central notch unusually variable in number; I have seen specimens with only two on each side, with four on each side, with five on one side and four on the other, with five on one side and none on the other, and with six on both sides; hence the total number ranges from four to twelve. Mandibles, with the fourth and fifth teeth small, or quite rudimentary. Maxillæ, with scarcely even a trace of a notch under the upper pair of spines. Cirri; first pair, with one ramus one third or one fourth longer than the other; in one specimen the number of segments were nine and sixteen in the two rami: second and third cirri short, very nearly equal in length, having in the just-mentioned specimen respectively ten and eleven segments; the sixth cirrus in this same specimen had twenty-five segments, each segment being about as long as broad, and supporting six pairs of spines. In the singular variety (a) the posterior cirri are more elongated, and each segment supports seven or eight, and in one case even ten pairs of spines! the third pair is also in this variety proportionally rather longer. At the base of the third pair there is a tuft of fine spines. The penis has not, as in B. crenatus, a point at its dorsal basis. The branchiæ are very little plicated.

Varieties.

Of the varieties having much elongated, club-shaped, hour-glass shaped, and depressed shells, there is no necessity to say anything in particular. With respect to the remarkable variety (a), I at first named and described it as a distinct species: I have received two lots, both from North America, one being sent me by Professor Agassiz from Cape Cod. These agreed in having the parietes permeated by regular tubes; in having the spur of the tergum most sharply pointed; in the third pair of cirri being proportionally longer compared with the second pair; in the sixth pair having more numerous segments, namely, three times as many as in the third pair; in the segments of the posterior cirri being more elongated, and especially in the number of pairs of spines on each segment--amounting in one case even to ten, a number unparalleled in other cirripedes. It may naturally be asked why I have not retained so well marked a form as a distinct species? In the first place, I found the most remarkable character in var. (a), namely, the number of pairs of spines on the posterior cirri variable, there being in one lot seven or eight pairs, and in the other lot nine or ten pairs on each segment. Secondly, all the characters by which this variety differs from the common B. balanoides, are those which are variable in the latter; this is especially the case with the structure of the parietes, and in a lesser degree with the spur of the tergum. Thirdly, I found a specimen in Mr. Cuming's collection, from Sweden (so that this var. (a) is not confined to North America), in which the cirri quite resembled those of the American specimens, but the spur of the tergum was in an intermediate condition as compared to that of ordinary varieties; and the parietal tubes were of unequal sizes, and scarcely more regular than sometimes in the true B. balanoides. And lastly, I have seen specimens from Ayrshire, with the parietes permeated by regular tubes, but with the tergum in an intermediate condition, and with the segments of the posterior cirri not more numerous or more elongated than in B. balanoides, supporting only six or seven pairs of spines, that is only one more than is common with B. balanoides; so that it was impossible to decide whether to rank the Ayrshire specimen under var. (a) or under the common form, so that I was compelled to give up var. (a) as a species.

Monstrous individuals, with the male organs aborted: Parasite.--Amongst some specimens, chiefly elongated ones, sent to me from Tenby, in South Wales, I found no less than seven individuals with some of the posterior cirri distorted, unequal on the opposite sides, and in an almost rudimentary condition, and in each case with the penis truncated, without any muscle entering the stump, which was absolutely imperforate: the vesiculæ seminales were much shrunk; in one case without any zoosperms; in another case with headless zoosperms cohering in an unusual manner; hence it is certain that these individuals were functionally only female, and could not impregnate their own ova; yet in two instances the ova had been impregnated, no doubt by neighbouring perfect individuals, for they contained well-developed larvæ. Several of these monstrous individuals were infested by one, two, or three curious crustaceans, which have been described by Mr. Goodsir,[97] as the male of the Balanus; but these supposed males are females, and were distended with ova containing almost mature larvæ; I believe that they are the females of the unnamed genus, belonging to the family of Ioniens, described by Mr. Goodsir, which live parasitic within the sack (as I likewise found) of the same individual Balani.

[97] 'Edinburgh New Philosophical Journal,' July, 1843.

Diagnosis.--I have seen several specimens of this species and of B. crenatus, absolutely undistinguishable in external appearance. I may specify one of B. balanoides, imbedded in an alcyonidium, and one of B. crenatus, imbedded in a sponge, and therefore neither at all abraded. Generally, the tips of the scuta in B. crenatus are a little reflexed, whereas in B. balanoides, when the shell has been at all disintegrated, the tips form a square projection locked into the terga. Bal. crenatus never assumes the punctured appearance so common in B. balanoides. Very young specimens of the latter can be distinguished by their dead white colour and smoothness. The edges of the radii are almost always smoother than in B. crenatus, and they are never so wide as is sometimes the case with B. crenatus. When a specimen is disarticulated, our present species can at once be distinguished from B. crenatus (and from B. improvisus), by its membranous basis, and by the solid or cancellated walls, which are rarely permeated by regular tubes or pores; and the walls when porose are not internally ribbed. I have already pointed out the few very trifling points, in which the opercula of the two species differ. The mouth and cirri offer likewise very few differences: in B. balanoides there are often more teeth on the labrum than in B. crenatus; the rami of the first cirri are perhaps here rather less unequal; the second and third pairs of cirri are certainly in most cases more equal in length; and lastly, the segments of the sixth cirri, even in the common varieties, bear, in equal-sized specimens, more pairs of spines than in B. crenatus. We shall see that in habits, with regard to depth, the two species differ, B. balanoides inhabiting much shallower water than B. crenatus.

Range, Habitats, &c.--This species is extraordinarily abundant within the tidal limits round the shores of Great Britain, and apparently of the northern United States. Besides numerous specimens sent to me from very many English localities, the late Mr. W. Thompson, of Belfast, kindly placed in my hands his very large collection; from these materials it appears that B. balanoides is the only tidal species in the northern parts of our island; but in the south and south-west, it is associated with the Chthamalus stellatus and Balanus perforatus. I doubt whether this species ever lives below the lowest tides; the case of a few specimens being mingled with B. improvisus and crenatus, (mentioned under the latter species,) at the bottom of a rudder of a small vessel, about six feet deep, is hardly an exception, for the water would there be troubled and aërated almost as in a breaker; and on this very rudder the upper two or three feet were coated exclusively by the B. balanoides. This species lives on rocks at both the uppermost and lowest limit of the tides; I am informed by Mr. Thompson, that he has seen specimens attached to a spot not covered by water during neap-tides. As a proof of its tenacity of life, Mr. Thompson informs me that he accidentally kept some specimens in a box, in a warm sitting-room, and found them alive seven days afterwards. This same most accurate observer finds, however, that B. balanoides is very susceptible to brackish water; he says, "that having kept some specimens alive for a week in excellent health, the water being changed once in thirty-six hours, they were one day killed instantly by some water, though brought from the same part of the estuary as usual, having been rendered brackish by much rain having lately fallen." I may recall the fact, that B. improvisus lives daily for hours in absolutely fresh running water.

The B. balanoides lives attached, often continuously coating many square feet of the surface, to rocks, pebbles, wooden-piers, littoral shells and ulvæ. The most northern point whence I have received specimens, is in lat. 66° 34′ in North America, collected by Mr. Sutherland; and the most southern point is Delaware Bay, in the United States, in lat. 39°; I do not believe that this species extends into the Mediterranean, for Ranzani (Mem. di Storia Nat.), who particularly attended to the nature of the basis, was not acquainted with any Balanus having a membranous basis; and Poli (Test. Ut. Siciliæ,) describes only two species thus characterised, and these are manifestly Chthamali.

With respect to the rate of growth of this species, I am indebted to Mr. W. Thompson for the following note:--

"Sept. 29, 1848.--I examined a great number of Balani, in reference to the growth made by them during the present season, and found it to average three lines in diameter, and at most four lines. I saw a few minute specimens, only one line in diameter, showing that the species continued to breed until lately: these latter were probably not more than four weeks old. The young of the present year are plainly distinguished from the older ones, by their pure white colour and fresh appearance. Judging from the size of this year's specimens, and of the older ones on the same stones, I am of opinion that the term of life of the species is two years. Of the older shells, which I examined and found living in the spring, nine tenths are now dead, the walls only remaining, the opercular valves having been washed away."

Mr. Thompson goes on to say, that the individuals which had, on July 3, a basal diameter of from two and a half to three lines, had attained, by the 30th of September, a diameter of four and a half lines, this being here the maximum size of the species.

30. BALANUS CARIOSUS. Pl. 7, fig. 3 a-3 e.

LEPAS CARIOSA. Pallas. Nova Acta Acad. Scient. Petrop. tom. ii (1788), p. 240, Tab. 6, fig. 24.

Parietes thick, formed by several rows of unequal-sized pores. Tergum narrow, with the apex beaked, and spur sharply pointed.

Hab.--Columbia River, west coast of North America, Mus. Brit. and Cuming; Behring Straits (Capt. Kellett); the Kurile Islands, according to Pallas. Attached to shells, and to each other in groups.

General Appearance.--Shell steeply conical, with a rather small oval orifice; or cylindrical, with a large rhomboidal and little toothed orifice. Colour dirty white. Surface either simply rugged, or more commonly covered by numerous, narrow, extremely prominent, longitudinal plaits; from the manner in which these overlap each other, the shell almost appears as if thatched with straw. The upper corroded part of the shell usually exhibits a cancellated and finely punctured surface. The radii are generally very narrow, forming towards the base of the shell a mere narrow ribbon to each compartment, and often hardly distinguishable; but in one specimen they were of considerable width: in the former case, the alæ are often widely exposed. The largest specimen which I have seen was 1.5 of an inch in basal diameter, but Pallas gives 2.2 as the measurement of a specimen from the Kurile Islands.

The opercular valves are united to each other and to the shell by unusually strong membrane; and the upper parts of both valves, in all the specimens seen by me, have been much disintegrated. The Scutum, in old specimens, is faintly striated longitudinally, but in some there is hardly a trace of this: the occludent margin is furnished with a few large knobs, not corresponding with every alternate line of growth (as is usual with other species), but with every fourth or fifth line. Internally, the articular ridge is moderately prominent (in young specimens more prominent) and reflexed. The adductor ridge is sharp and prominent; in the upper part it is confluent with the articular ridge, but in young specimens can be seen to be distinct; in the lower part it borders a large deep cavity for the lateral depressor muscle, in the middle of which there is a very slight longitudinal ridge; this cavity sometimes is almost closed or arched over in its upper part. In one specimen, the basal margin of the scutum was deeply hollowed out in the middle. The Tergum is remarkably narrow, with its apex produced into a triangular beak, hollow within, and sometimes faintly tinged purple. A deep, closed, longitudinal furrow runs down the valve. The spur is long, remarkably narrow, and pointed. Internally, the spur is produced up the valve as a ridge: the inflected scutal margin, and the prominent articular ridge, are both nearly straight, and parallel to the spur. The crests for the depressores are sharp and very prominent.

The Parietes are very thick and strong: unlike every other species of the genus, they consist of several very irregular rows, of unequally sized, round or angular tubes (3 b). These tubes or pores are generally short, and are at frequent intervals crossed by transverse septa; they often rather deserve to be called cells than tubes. New tubes are formed along the inner as well as along the outer lamina. They are lined by dusky purple corium. The internal surface of the parietes is smooth in the upper part, and in the lower, it is reticulated by slight, irregularly branching ridges. The carinal internal margin of each compartment projects a little, as in the case of B. crenatus and balanoides. The lower edge of the sheath is either hollow beneath, or is united to the walls. The radii in one specimen were broad, with slightly oblique, jagged summits; generally they are extremely narrow, forming more ribbons along the lower edges of the compartments, barely extending up as high as the sheath. They can sometimes hardly, or not at all, be seen, until the shell is disarticulated: in rather young specimens the sutural edge is sometimes quite smooth; in old specimens the lower part of the edge has coarse arborescent septa, with the interspaces filled up solidly, whilst the upper part is smooth. The alæ are conspicuous from the outside, owing to the little development of the radii; but owing to the diametric growth not having been great, the part added during such growth is narrow; the summits of the alæ are only slightly oblique: the sutural edge is coarsely crenated, with the teeth denticulated or slightly arborescent.

Basis membranous.

Mouth: labrum with only four very minute teeth: mandibles with four teeth; the third tooth broader than the first; the fourth small. Maxillæ, with the two upper spines placed on a slight prominence, beneath which there is a small notch. Cirri of a very dark colour (much injured): the segments of the first, second, and third pairs very broad and short, protuberant in front, and most thickly clothed with spines; the third pair is very little longer than the second pair: the sixth pair (in a large specimen above one inch in basal diameter) had the segments broader than long, each furnished with seven pairs of spines.

Affinities.--This species, though very distinct, evidently comes near to B. balanoides, especially to var. (a). By merely doubling or trebling the irregular rows of short tubes in the walls of B. balanoides, with their reticulated inner lamina and longitudinally folded outer lamina, we should have the structure exhibited in B. cariosus. We have seen, also, that in var. (a) of B. balanoides, the spur of the tergum is remarkably sharp, as in B. cariosus. This species, also, in a very marked manner approaches in many characters, especially in the opercular valves, in the cirri, and to a certain extent in the shell and basis, to B. flosculus, and even in external appearance to var. sordidus of the latter--an inhabitant of the opposite extremity of the continent, namely, of Tierra del Fuego. Again, the tergum to a certain extent, and the scutum in a singular manner, resemble these valves in B. nubilus, showing an unequivocal affinity to that species. With respect to the most remarkable character of the species, namely, the several irregular rows of tubes or pores in the walls, it deserves notice that in B. crenatus, which is certainly closely allied to B. balanoides, the longitudinal septa sometimes divide near the outer lamina, thus giving rise to a few additional tubes. Of the above several species, to which our present species is allied, B. flosculus stands in the next section, and B. nubilus and crenatus in the last: hence we see that B. cariosus has singularly divergent affinities. The peculiar structure of the parietes, together with the general appearance of the shell, made me at the first moment suppose I was examining a Tetraclita (or Conia of Leach); hence, also, it has arisen, that Lepas cariosa of Pallas has often been quite erroneously given as a synonym of Tetraclita porosa.

31. BALANUS DECLIVIS. Pl. 7, fig. 4 a-4 d.

Parietes solid; rostrum nearly twice as long as the carina or carino-lateral compartments, hence the basis is oblique. Tergum with the spur truncated, half as wide as the valve.

Hab.--West Indies; Mus. Brit.--Jamaica, imbedded in a sponge; Mus. Cuming.

This is a remarkable species; when first seeing it imbedded in numbers in a sponge, I did not in the least doubt but that it was an Acasta: on examination, however, it is found to have a membranous basis, and therefore cannot by the definition enter into that sub-genus, to which, however, it is very closely allied. It differs from other sessile cirripedes very remarkably in the rostrum being nearly twice as long as the carinal compartments, so that the basis is always very oblique, or placed almost on one side; in this elongation of the rostrum, although in a different direction, we are reminded of B. calceolus and its allies; and these latter we know can hardly be separated from certain species of Acasta. Hence the position of our present species in this section, is not natural; but I am unable to place it elsewhere, without breaking down every definition: it should stand somewhat isolated, on one side of a line of affinity connecting Balanus calceolus and navicula with Acasta purpurata.

General Appearance.--The shell is thin, fragile, smooth, and white, but covered to a considerable extent by a brown membrane, which on the sheath and opercular valve is of a bright tint, and clothed with bristles. Viewed laterally, the rostrum is seen to be considerably bowed, and from its being nearly twice as long as the other compartments, with its lower end bluntly pointed, the basal margin of the whole shell is rendered very oblique, forming a slightly concave line. The lateral compartments are rather longer, and about one third broader than the carino-lateral compartments. The rostrum, from terminating downwards in a blunt point, instead of being square or truncated, as in all other Cirripedes, and from the upper end being, as is usual, pointed, has, when disarticulated from the other compartments, the shape of a boat. The parietes are not at all porose: their internal surface sometimes shows traces of longitudinal ribs, but sometimes there are none. The radii are narrow, with their summits very oblique, and their sutural edges smooth. The sutural edges of the alæ are likewise smooth. The largest of Mr. Cuming's specimens was .2 of an inch in diameter; but a disarticulated specimen in the British Museum must have been larger, having a rostrum .3 in length. The Basis is membranous.

The Scuta are rather convex; they have their lines of growth approximate, most finely crenated, so as to be very feebly striated longitudinally. Internally, the articular ridge is pretty well developed, its lower edge being very oblique; there is barely an adductor ridge: the pit for the lateral depressor muscle is deep. The spur of the Tergum is placed close to the basi-scutal angle of the valve; it is about half as wide as the valve, with the lower end truncated: sometimes it may be rather said to be bluntly pointed, owing to its carinal side sloping up to the basal margin. The articular ridge is pretty well developed. The crests for the depressor muscles are barely discernible.

Animal's body unknown.

Section F.

Parietes and radii not permeated by pores; basis sometimes permeated by pores, sometimes not permeated, sometimes excessively thin and hardly distinguishable.

32. BALANUS HAMERI. Pl. 7, fig. 5 a-5 c.

LEPAS HAMERI. Ascanius. Icones rerum naturalium, Tab. 10, 1767.

---- TULIPA. O. F. Müller. Prodromus. Zoolog. Dan. 1776; sed non L. tulipa, in Poli, Test. ut. Siciliæ; neenon B. tulipa, in Bruguière, Encyclop. Method; neenon B. tulipa, in Sowerby, Genera of Shells.

---- TULIPA ALBA. Chemnitz. Syst. Conch. Tab. 93, fig. 832.

---- FOLIACEA. Spengler. Skrivter of Naturhist. Selskabet, 1 B. 1790.

BALANUS CANDIDUS. (Tab. emendata) Brown. Conch. Great Britain (1827), Tab. 6, figs. 9 and 10, et 2d edit. Tab. 54, figs. 9-12.

---- TULIPA. Lyell.[98] In Phil. Transact., 1835, p. 37, Tab. 2, figs. 34-39.

[98] Sir C. Lyell remarks that this is apparently the B. Uddevallensis (Linn.) of Swedish lists of fossils. Prof. E. Forbes has shown (Mem. Geolog. Survey of England, vol. 1, p. 364) how this name arose, from a short description, prior to the introduction of the binomial system, "Lepas quæ Balanus Uddevallensis," given by Linnæus in his Wast-Gotha Resa, in 1747.

For the reference to Ascanius' work, which is on the binomial system, and subsequent to the 10th edit. of Linnæus, in 1758, I am greatly indebted to Mr. Sylvanus Hanley. Had it not been for this gentleman, I should have used Müller's name of B. tulipa as the first name.

Shell white: radii with their oblique summits smooth and arched; sutural edges smooth: basis solid. Scutum feebly striated longitudinally: tergum with the spur narrow.

Hab.--Coast of Yorkshire; Scotland; Galway, Ireland; Isle of Man, and Anglesey, twelve fathoms. Generally in deep water; not very common. George's Bank, Massachussetts, United States; Mus. Aug. Gould. Iceland, Finmark, and the Faroe Island, according to Spengler. Attached to crustacea, mollusca, stems of fuci, and stones; often associated with B. porcatus and crenatus.

Fossil.--In glacial deposits at Uddevalla in Sweden, and Beaufort in Canada; Mus. Lyell. Banks of the Dwina, Russia; Mus. Murchison. Greenland, "in blue clay," according to Spengler. Red Crag (Sutton) Mus. S. Wood.

General appearance.--Shell tubulo-conical, very smooth, white, generally more or less covered by yellow thin membrane: orifice large, sub-triangular: radii moderately broad, with their more or less oblique summits slightly rounded and smooth; from this circumstance the shell has been justly compared to the half-opened flower of a white tulip. Specimens often exceed an inch in basal diameter; I have seen one from Scarborough two inches in diameter and one and three quarters in height: another specimen was 1.6 in diameter and 3 in height. The specimens in the glacial deposits seem even to have acquired larger dimensions, one from Uddevalla being nearly four inches in height.

Scuta, elongated, flat, feebly striated longitudinally: internally, articular ridge short, moderately prominent: adductor ridge, confluent in the upper part with the articular ridge, running straight down and forming a rather large cavity for the lateral depressor. Terga feebly striated longitudinally, with a longitudinal furrow, having the sides, in old specimens, partly closed in: the basal margin slopes much towards the spur, which is rather long and narrow, with its end rounded: it is placed at about its own width from the basi-scutal angle. Internally, articular furrow narrow; crests for the depressores moderately prominent, but in a variable degree.

Compartments: these are unusually thin, and separate easily: the parietes are finely ribbed longitudinally on their insides; the bases of these ribs being just perceptibly denticulated. Radii, with their summits oblique (usually at about an angle of 45°), slightly arched and quite smooth: the smoothness is produced by the edge being a little inflected: sutural edge quite smooth, without even a trace of septa or denticuli. Alæ oblique, generally rather less oblique than the summits of the radii: sutural edges smooth, with an excessively fine linear furrow running along the edge, a little towards the inner side, and filled with a yellow ligamentous substance: a furrow of this kind I have seen in no other species.

Basis, solid, not permeated by pores; either smooth, or slightly furrowed in lines radiating from the centre.

Mouth: labrum with scarcely perceptible minute bead-like teeth thinly scattered along the edge. Palpi and outer maxillæ rather sparingly clothed with hairs. Mandibles with teeth rather sharp; the fourth and fifth teeth small, but well developed; inferior angle pointed with fine spines. Maxillæ with a deep notch under the two upper great spines. Cirri, the first pair is short, with rami of nearly equal length: the segments are not protuberant in front either in the first or second pairs. In the posterior cirri, the segments bear four pairs of spines, with a tuft of rather long intermediate spines: in young specimens there are only three pairs: the spines in the dorsal tufts are short and thin.

When the shell is disarticulated, this species cannot be confounded with any other; but judging by external characters alone, it may sometimes be very easily confounded with B. eburneus, and I have received the two species under this one name from Massachussetts: generally B. Hameri may be distinguished from B. eburneus by the smoothness of the summits of its radii, and by the so-called epidermis being of a darker yellow.

With respect to the fossil specimens from the glacial deposits, I have little to add; I have seen one from Uddevalla, as already remarked, four inches in height, and a lateral compartment broader by one fourth than the same compartment in any recent specimen. As Sir C. Lyell remarks (Phil. Transact.), the compartments are always found separated, which is accounted for by their weak union in a recent state. This species, when fossil, is usually associated with its deep-water congeners B. porcatus and crenatus, as at the present day.

I must here mention that I have examined a considerable number of separated compartments, without opercular valves, brought from Barbados, in the West Indies, showing the existence there of a closely allied or possibly identical species. The only difference which I can point out in these compartments is, that the parietes are rather thicker, and the radii rather narrower, with more oblique summits: some of the compartments are two inches in length. It seems very improbable that the true B. Hameri should extend to the West Indies, but after what has been seen in the case of B. crenatus, this is possible.

33. BALANUS AMARYLLIS. Pl. 7, fig. 6 a-6 c.

Shell striped or clouded with pinkish-purple, or quite white; radii narrow, with their oblique summits smooth or arched: basis porose. Scutum plainly striated longitudinally: tergum with the spur narrow.

Var. (a):[99] bright rosy pink, not distinctly banded longitudinally. Hab. North-east coast of Australia.

Var. (b): snow white, glossy; orifice deeply toothed.

[99] This variety perhaps is the B. roseus of Lamarck, as figured in Chenu, 'Illust. Conch.' Tab. 2, fig. 9; but as Lamarck does not even notice such conspicuous external characters as the longitudinal striæ on the scuta, and the smooth rounded edges of the radii, it is impossible to identify his species.

Hab.--Mouth of the Indus; East Indian Archipelago; Philippine Archipelago; Moreton Bay, and the north-east coast of Australia. Attached frequently on ships' bottoms, associated with B. tintinnabulum and amphitrite. Sometimes attached to Gorgoniæ with B. calceolus.

General Appearance.--Shell steeply conical, with the orifice sub-rhomboidal, moderately large, very slightly, or deeply notched: surface very smooth: white, longitudinally banded with pinkish or leaden purple, with sometimes a purplish, sometimes a yellowish tint, the latter owing to the persistent epidermis; the bands are pale, and often fade away in the lower, and sometimes in other parts of the shell; the epidermis is generally more persistent on the narrow rounded radii than on the parietes, and hence the radii are generally yellowish. The opercular valves are pale dull purple: the sheath is darker purple, with the exception of the portions of the alæ added during the diametric growth, which are of a dead white, and are externally conspicuous. The scuta are striated longitudinally. I may remark, that, excepting the narrowness of the radii, with their quite smooth, rounded and very oblique summits, some specimens are hardly distinguishable, in external aspect, from varieties of B. amphitrite. If the specimens from the north-east coast of Australia, of which I have seen many (but unfortunately only one small one had its opercular valves), form, as I fully believe, merely a variety; it is characterised by its nearly uniform beautiful rosy pink, without any distinct longitudinal bands: of these specimens I have seen one two inches in basal diameter, and three in height: of ordinary duller-coloured striped specimens, the largest was 1.7 in basal diameter. Of the perfectly white var. (b), I have seen several specimens, the largest being .6 of an inch in diameter: these have a somewhat peculiar aspect, but I have met with only one specimen with opercular valves, and that was extremely young: I at first considered this form as specifically distinct; but I can point out, after careful examination of the whole shell, operculum, and internal animal of the young specimen, no sufficient diagnostic characters.

Scutum, plainly striated longitudinally, with the striæ dividing the prominent lines of growth into squarish beads: internally, the upper part of the valve is roughened: the articular ridge is short, remarkably little prominent, and not reflexed; the adductor ridge is blunt and little prominent; sometimes it is almost confluent with the articular ridge: there is a deep but variable depression for the lateral depressor muscle; and in young specimens of var. (a) it was almost absent. Tergum: the surface exhibits traces of longitudinal striæ: there is a deep longitudinal furrow, with the sides folded in and quite closed in full grown specimens: the scutal margin is considerably curved towards the scutum. The spur is long and narrow, with the end bluntly pointed, placed at rather above its own width from the basi-scutal angle; the basal margin slopes but little towards the spur: the crests for the depressores are feebly developed.

Parietes: their internal surfaces are strongly ribbed longitudinally, with the basal ends of the ribs coarsely denticulated, and with the denticuli extending close to the outer lamina. The radii are generally narrow, but their width varies; their summits are very oblique, smooth, rounded, and inflected, with the lines of growth, in the uppermost part, curving inwards; their sutural edges, in the upper inflected portion, are quite smooth, without septa; in the lower and larger portion, the edge is crenated with excessively fine teeth or septa, not denticulated: the radii, like the parietes, have no inner lamina: the recipient grooves in the opposed compartments are smooth, and are in the lower part of the shell of unusual depth. The alæ, differently from the radii, generally have their summits very slightly oblique, but sometimes they are highly oblique: their sutural edges are most finely crenated. The basis is generally flat, sometimes cup-formed; it is permeated by pores, crossed by transverse septa; and sometimes there is an underlying cancellated layer.

Mouth: labrum with either six very small teeth, or with none. Mandibles (Pl. 26, fig. 5), with the third tooth a little thicker than the first; fourth and fifth teeth small, but quite distinct. Maxillæ (Pl. 26, fig. 7), with the inferior part forming a square step-formed projection, bearing, one behind the other, two spines as long as the upper pair; in a young specimen of var. (a) this step-formed projection was absent.

Cirri: first pair with the rami unequal by about four segments: the shorter ramus has the segments very protuberant in front, thickly clothed with strongly serrated spines; the second cirrus has segments moderately produced; the third has them produced only in a slight degree. The pedicels of the second and third cirri have dorsal tufts of spines, but not a hairy plate prolonged over the thorax. The posterior cirri have segments broader than long, bearing only two pairs of nearly equally long spines; and between each pair there is a small intermediate tuft. The penis has the usual basi-dorsal point.

B. amaryllis is a distinct and well-defined species, more nearly related to B. Hameri than to any other form.

34. BALANUS ALLIUM. Pl. 7, fig. 7 a-7 d.

Shell faintly tinged with purple: radii broad, with their summits not oblique: basis not porose. Scutum with the lines of growth crenated: tergum with the spur extremely short, truncated, broad as half the valve.

Hab.--Raine's Islet, Barrier Reef, Australia, Mus. Stutchbury. Hab. unknown, attached to and coated by Porites. Mus. Brit.

General Appearance.--Shell conical, smooth, but with the lower part sometimes narrowly ribbed in lines corresponding with the internal longitudinal ribs; tinted pale peach-blossom purple, owing to the sheath being finely so coloured; or wholly white. Radii broad, white, square on the summit, hence orifice entire, ovate passing into rhomboidal. The parietal portion of the carino-lateral compartments extremely narrow, about one eighth of the width of the parietes of the lateral compartments. Basis concave, partially imbedded in the coral. Largest specimen .35 of an inch in diameter.

There are some specimens in Mr. Cuming's collection which appear to belong to this species, and are certainly very closely allied to it, but not having the opercula, cannot be identified positively; the shell is flatter, with the walls strongly ribbed up to the orifice, which is more rhomboidal: the basis is much more cup-formed and more deeply imbedded in the coral; but these differences by themselves are by no means sufficiently diagnostic.

Scutum: the lines of growth are crenated, causing the surface to be very obscurely striated longitudinally: the articular ridge is very prominent, as can be best seen from the outside, and runs down the whole length of the tergal margin with a very regular curve, and hence differs from the articular ridge in the foregoing species. The adductor ridge is either absent, or very indistinct, and parallel to the articular ridge: there is a deep little pit for the lateral depressor muscle. Tergum (7 d), with the apex somewhat produced or beaked, and tinged purple: external surface almost flat, without any longitudinal furrow: scutal margin curved. Spur very short, placed quite close to the basi-scutal angle of the valve; broad as half the valve; lower end square. Internally, the articular ridge is prominent only in the uppermost part of the valve: crests for the depressores very feeble.

Parietes: their internal surface is very strongly ribbed longitudinally, the ribs being coarsely denticulated at their bases, and finely fluted along their sides. The sheath is transversely ribbed, and clothed with an epidermis furnished with transverse rows of fine hairs. The radii are of a dead white, whereas the parietes are translucent; the summits are parallel to the basis; they are broad; the radii of the carino-lateral compartments appear extraordinarily broad, owing to the narrowness of the parietal portion: the sutural edges are furnished with coarse septa, which are sinuous, irregular, and obtusely denticulated; the interspaces are filled up solidly. The alæ are thin, with their sutural edges almost smooth, and their summits oblique: in some specimens, during the diametric growth, a mere, almost thread-like ribbon is added to their sutural edges. Basis slightly cup or saucer-shaped; moderately thick, permeated by fine pores, and generally ribbed in lines radiating from the centre. The walls and basis adhere together very firmly.

Mouth: labrum with six teeth: mandibles with five teeth; the three upper teeth being sharp, narrow, and unusually prominent; the two lower teeth minute and sharp; maxillæ without a notch. Cirri much injured: first pair with one ramus apparently one third longer than the other: segments not very protuberant: the posterior cirri have elongated segments with five pairs of spines.

Affinities.--This species is very distinct from all the foregoing: in the carino-lateral compartments being so narrow, and tending, as we may suppose, to become aborted; in the form and structure of the whole shell, and in its habits, this species shows an affinity and passage to the coral-inhabiting sub-genus Creusia, which has only four compartments. There is also a close affinity to the sub-genus Acasta. This species is so closely allied to the following, that I at one time felt some doubts whether they ought to have been specifically separated; it is also probably closely allied to B. terebratus, but the materials hardly suffice for judgment: it is also related, though less obviously, to B. vestitus.

35. BALANUS CEPA. Pl. 7 fig. 8 a-8 c.

Shell dirty reddish-purple, steeply conical: radii narrow: basis obscurely porose. Scutum with the lines of growth crenated: tergum with the spur truncated, broad as half the valve, and depending beneath the basi-scutal angle as much as half its own breadth.

Hab.--Japan, attached to an Isis, Mus. Cuming. Attached to an oyster, Mus. Stutchbury.

As already stated, this species comes in all essential respects very near to the last, though differing much in appearance; I have seen two sets of specimens, and two sets of B. allium, and there was no variability or passage in the points in which they differed; hence I must consider them as specifically distinct.

Shell, steeply conical, strongly but bluntly ribbed longitudinally; coloured either all over dull reddish purple, or with the upper part only pinkish purple: in one set of specimens, the yellow epidermis was partially persistent. Radii narrow. Orifice small, ovate. The wall of the carino-lateral compartment is very narrow. The internal surface of the parietes is ribbed, but finely, and only in the lower part. The septa, on the sutural edges of the radii, are finer than in B. allium. Basis flat, obscurely permeated by pores. The largest specimen is .25 of an inch in basal diameter.

Scuta: these are longitudinally and finely striated; the basi-tergal corner is more rounded off than in B. allium, and the articular ridge is not nearly so prominent: internally, the adductor ridge is rather more prominent. The Tergum is rather broader: its apex is produced into a minute sharp point: the scutal margin is straight; the spur is broader, and measured from the basi-scutal angle of the valve, considerably longer; namely, as long as half the width of the basal margin of the spur, whereas in B. allium it is only about a quarter as long as the basal margin of the spur: the lower edge of the spur is not here so directly transverse to the longitudinal axis of the valve as in B. allium: the external surface is not so flat as in that species, and a depression runs down to the basi-scutal angle of the spur.

Considering the difference in the shape and appearance of the shell, with its narrow radii and small orifice; considering the less strongly ribbed internal lamina of the parietes, the finer septa on the sutural edges of the radii, the slight difference in outline in the scuta and terga, more especially the greater length of the spur, I conceive I am right in ranking this form as a distinct species, though assuredly it is very closely allied to B. allium, and even still closer to the following B. quadrivittatus.

36. BALANUS QUADRIVITTATUS. Pl. 8, fig. 1.

Shell steeply conical, having four longitudinal gray bands placed crosswise: radii with their summits oblique: basis thin, solid. Scutum, with the lines of growth smooth; no distinct pit for the lateral depressor muscle: tergum as in B. cepa.

Hab.--East Indian Archipelago, attached to lamelliferous corals, and associated with Pyrgoma grande and Creusia spinulosa, Mus. Brit. and Stutchbury and Darwin. Philippine Archipelago, attached to a Tetraclita, Mus. Cuming.

I have seen four sets of specimens of this species, taken in four different places, one set containing above twenty individuals, and all resembled each other exactly: nevertheless, this species comes so close to B. cepa, that I am somewhat doubtful about its specific distinctness.

General Appearance.--Shell smooth, or slightly folded, steeply conical; white, with four longitudinal bands of pale brownish-gray colour, namely, on the rostrum, the carina, and the two lateral compartments: the carino-lateral compartments are very narrow and almost white: the four brownish-gray bands are darkest in the upper part of the shell, though always rather faint, and die out towards the base: they can sometimes be seen to be formed of several narrow longitudinal stripes; the tint shows a trace of containing purple. The orifice of the shell is small, rhomboidal, and not quite entire, owing to the obliquity of the summits of the moderately broad radii. In structure, the shell, radii, and alæ resemble those in the last species. The basis, however, does not appear to be permeated by pores. Basal diameter of largest specimen .25 of an inch.

The Scuta most closely resemble those of B. cepa, but the lines of growth are not crenated, and internally there is only a very minute pit for the lateral depressor muscle, placed almost on the edge itself of the valve. The Tergum hardly differs at all from that of B. cepa, but is perhaps of rather greater breadth.

The Mouth does not differ from that in the last two species. In the Cirri, the three posterior pairs have elongated segments, bearing only three pairs of spines, of which the lowest pair is minute: in B. allium, and I believe in B. cepa, there are five pairs of spines on each segment.

This species differs from the last only in the peculiar colouring, smoother walls, more oblique radii, solid basis, and more especially in the scuta having the lines of growth not crenated, and internally, in the pit for the lateral depressor muscle being so very minute and placed on the basi-tergal edge of the valve. The posterior cirri, also, I believe, differ in the number of the spines which the segments support; nevertheless, I cannot feel confident about the specific distinctness of B. quadrivittatus.

37. BALANUS TEREBRATUS. Pl. 8, fig. 2 a-2 b.

Shell white, strongly ribbed longitudinally, with the basal margin produced into long points: basis concave, not permeated by pores, but strongly ribbed externally in radiating lines; the interspaces between the ribs being riddled by minute rounded apertures, often placed in double rows.

Hab.--Unknown, Brit. Mus., attached to a lamelliferous coral.

I have in this instance broken through my rule of not describing a Cirripede without examining the opercular valves; but the species here named is so peculiar, that it would have been a fault to have passed it over. There is but a single specimen in the British Museum, without, as just stated, the operculum, and of course without the animal's body.

Shell, white, depressed, conical, somewhat elongated in its rostro-carinal axis; orifice rather small, pentagonal, toothed, elongated. Parietes rather thin, with extremely prominent longitudinal ribs, produced at the basal edge into long spikes: the internal surface is also ribbed, but less strongly than the outside. Radii rather narrow, with oblique, not smooth summits; sutural edges very finely and obscurely crenated. Alæ with their summits extremely oblique. Lower edge of sheath closely attached to the walls. The carino-lateral compartments are rather narrow.

Basis, slightly concave or saucer-shaped; the circumference is produced into long spikes, corresponding with those on the basal margin of the parietes: these projections equal half the semi-diameter of the shell. The internal surface of the basis has slightly prominent, rounded ridges; and the external surface has extraordinarily prominent, sharp ridges, radiating from the centre; the edges of the external ridges are irregular, notched, and knobbed. I have seen in no other species external ridges on the basis or surface of attachment; and what is more remarkable, the interspaces between the ridges are penetrated by small rounded apertures, of irregular shape and unequal sizes; and these are generally arranged in an irregular double row, and externally are closed by the membrane, which clothes the basis. In the sub-genus Acasta, the basal cup is sometimes penetrated by similar holes, but these seem never to extend over the whole basis, and are very variable; nevertheless, in some specimens of Acasta spongites from the Cape of Good Hope, portions of the basis closely resembled, except in the absence of the radiating ridges, the structure here described, but the holes were not arranged in any definite order. The internal surface of the parietes in Acasta sporillus presents a somewhat analogous appearance, but the pits do not penetrate through the walls. This species, I have no doubt, is closely allied to the sub-genus Acasta, and to Balanus navicula with its allies, and, but much less closely, to B. allium with its allies. Indeed, had B. terebratus inhabited a sponge, I should have been compelled to have ranked it in the sub-genus Acasta.

38. BALANUS VESTITUS. Pl. 8, fig. 3 a-3 b.

Shell pinkish-purple or white, clothed by an orange-coloured membrane; radii represented by mere fissures; basis solid. Scutum, with a sharp, curved adductor ridge; with crests for the lateral depressor muscle: tergum, with the spur short, truncated, one third of width of valve.

Hab.--New Zealand, New South Wales, Mus. Brit. and Stutchbury; attached to shells.

General Appearance.--Shape conical, often steeply conical; orifice small; radii not developed, represented by mere fissures. The walls are smooth, or slightly, or strongly ribbed longitudinally. The shell itself is of a fine peach-blossom pink, or nearly white, but it is generally covered by a thick yellow or brownish-orange epidermis. Opercular valves pinkish, but similarly covered. Basal diameter of largest specimen .7 of an inch.

Scuta, with the lines of growth closely approximate; surface somewhat convex. Internally, the articular ridge is very little prominent, but runs far down the tergal margin; in some specimens, however, it is shorter and more prominent. The adductor ridge is strongly prominent, is curved towards the rostral angle, and runs down nearly to the basal margin. The rostral depressor muscle is lodged in a small cavity, formed, as usual, by the overlapping of the occludent margin; within this cavity there are either tolerably distinct little crests, or merely traces of them, for the attachment of the muscle. The lateral depressor muscle is attached to several quite distinct crests, seated in a concavity beneath the adductor ridge. Tergum rather narrow, with the apex produced or beaked; the beak is purplish and flat. There is a slight rounded longitudinal furrow, or depression. The spur is fully one third of the width of the valve: it is short, with the end truncated, and placed close to the basi-scutal angle; the basal margin on the carinal side slopes gently towards the spur. Internally, the scutal margin is scarcely at all inflected, and the articular ridge is very little prominent: the crests for the tergal depressores are pretty well developed.

From the points here enumerated, it is clear that the opercular valves are articulated together much less strongly than is usual with most species, excepting B. allium and its allies. It is remarkable that in this species the terga are united to the sheath, not, as is usual, by a single opercular membrane, but by five or six, one above the other, the upper membranes not having been exuviated as each new lower one was formed. The minute spines on the membrane lining the sheath are rather larger and more numerous than is usual, and to the base of each spine a tubulus of unusual diameter runs, imbedded in the shell.

The Walls, internally, have unusually numerous, narrow, approximate, strongly prominent, longitudinal ribs, denticulated at their bases, and inserted into the furrows on the borders of the basis: in old specimens these internal ribs die out in the upper part of the walls. The Radii are not developed in any of the many specimens which I have seen, and the edges of the compartments on both sides of each suture are equally marked by slight, irregular ridges or knobs, answering to the septa and their recipient furrows, in the species with ordinarily developed radii. There is very little diametric growth, the orifice being gradually enlarged by the disintegration of the upper ends of the walls; the alæ, however, in some specimens, do grow a little along their lateral or sutural edges, so that some little diametric growth must be effected. The summits of the alæ are very oblique; their sutural edges are plainly crenated. The sheath descends about half way down the walls. The Basis is flat, not permeated by pores, but deeply furrowed in lines radiating from the centre.

Mouth: labrum sometimes with no teeth, sometimes with four minute teeth; mandibles with four teeth, of which the third is blunt and rather large; the fourth is a mere knob. Maxillæ; there is, as usual, an upper pair of large spines (beneath which there is sometimes a small notch), but all the lower spines, instead of standing as usual in pairs, form a single row. Cirri; first pair with the rami remarkably unequal in length, one ramus having twenty-two segments, and being more than twice the length of the other, having only nine segments: these segments, and likewise those of the second and third pairs, have an inverted conical shape; and they are all less thickly clothed with spines than is usual. The second pair is short, about as long as the shorter ramus of the first pair, and has ten or twelve segments. The third pair is above twice as long as the second pair, and contains twenty-four segments: this very unusual length is owing to the presence of numerous thin tapering upper segments, unlike those generally found in Balanus, in the third pair of cirri, and apparently serving as feelers. These upper tapering segments are of an inverted conical shape, and support on their upper margins two very small tufts of spines, one behind and one in front: on the segments lower down these tufts increase in size, and the spines are more spread out, so that in the basal segments, the tufts in front form on the upper margin two or three crowded rows of bristles. The three posterior pairs of cirri have elongated segments, which bear on their upper half three pairs of spines; of these the lowest pair is minute, and the middle pair is only one third of the length of the upper pair. The sixth cirrus, in the same individual as before, contained twenty-seven segments in each ramus, that is only three more than in the third cirrus! I must observe, that the cirri in all the specimens were irregular, often distorted and monstrous; and therefore, probably, there is considerable variation in the proportional numbers of the segments in the cirri.

At the base of the penis there is a minute, knife-edged, triangular projection. The branchiæ are rather narrow, pointed, and not very large.

Affinities.--This is a very distinct species, as shown by the peculiarities in the cirri, by the absence of radii to the shell, and by the presence of crests for the attachment of the lateral scutal depressores. With the exception of this latter character, the opercular valves clearly show, that B. vestitus is allied to B. allium, cepa, and quadrivittatus. In some respects this species manifests an affinity to B. imperator, which latter has its third pair of cirri nearly similar to those of B. vestitus.

39. BALANUS IMPERATOR. Pl. 8, fig. 4 a-4 c.

Shell internally imperial purple; parietes thick, with their internal basal edges rough with irregular points and ridges; radii narrow; basis very thin, solid. Scutum, with crests for the rostral and lateral depressor muscles; tergum, with the end of spur rounded.

Hab.--New South Wales, Sydney, Port Stephens, Moreton Bay; attached to sandstone-rocks and shells, at low-water line; Mus. Brit., College of Surgeons, Cuming, Stutchbury.

Shell conical, very thick and very strong; longitudinally sulcated more or less strongly; whole thickness of shell beautifully coloured rich violet, or more strictly "imperial purple;" externally the surface, from disintegration, is generally whitish; internally the colour is best developed: the narrow radii and the thin basis are white. The largest specimen which I have seen was one and three-quarters of an inch in basal diameter, the walls close to the basis being, in this instance, actually .3 of an inch in thickness.

Operculum thick and strong, covered by yellowish-brown epidermis; internally, the shelly substance is either all of the richest purple or yellowish-white, tinged, especially in the upper part, with purple. Scuta, with the apex beaked and somewhat reflexed; articular ridge very thick, little prominent; articular furrow very narrow, the impression made by the adductor muscle is seated very high up the valve; there is hardly an adductor ridge, but the surface of the valve is angularly prominent in a curved line, running from the articular ridge to near the rostral angle of the valve. At the rostral angle, the occludent margin is not folded inwards, as is generally the case, but the surface is flat, and is marked by four or five crests for the attachment of the rostral depressor muscle. There are other crests for the lateral depressor muscle. Tergum, with the apex somewhat produced and beaked, but blunt; longitudinal furrow shallow; spur of moderate breadth, with its lower end rounded; the basal margin on the carinal side of the spur slopes towards it. Internally, articular ridge moderately prominent. Crests for the tergal depressor well developed.

Parietes, solid, thick, with the basal internal edge (4 c) formed of short ridges, or flattened and irregular points, which in very old specimens are but little prominent; inner surface, finely, closely, and irregularly ribbed longitudinally, but in some specimens nearly smooth. The radii are nearly white; they are narrow, sometimes hardly at all developed, and have their summits very oblique and jagged; exteriorly, they are sulcated in a transverse direction, and sometimes form oblique steps, from having been formed layer over layer: their sutural edges are formed of irregularly branching crests or septa. The alæ have their summits very oblique; their sutural edges are thick and crenated: the part added during diametric growth on the inner surface is smooth, and has a different appearance from the transversely ribbed portions of the sheath, of which the alæ form a portion. The lower edge of the sheath is hollow beneath. The carino-lateral compartments are very narrow.

Basis calcareous, thin, white, sometimes opalescent, apparently formed by an aggregation of very minute calcareous beads, with no trace of furrows radiating from the centre.

Mouth: labrum hairy, with apparently some very minute teeth; mandibles, with the fourth and fifth teeth small and rudimentary; maxillæ rather broad, with a narrow and rather deep notch under the two great upper spines: outer maxillæ with the lower lobe very large.

Cirri: first pair, with the rami unequal by several segments: second pair, with the rami unequal in length by about six segments: third pair elongated, with the segments very numerous, almost equalling those in the sixth cirrus; upper segments of both rami much elongated, each with only a circle of spines; segments in the above first three pairs of cirri only slightly protuberant. Posterior cirri elongated, with the upper segments bearing three pairs, and the lower segments four pairs of main spines, between which there is a small intermediate tuft.

Affinities.--This noble Balanus, in all the characters derived from its opercular valves, and from its cirri, is closely allied to the last species: in the structure, however, of the shell and of the basis, it comes closer to the following, B. flosculus. The crests on the under side of the scutum, for the lateral depressores, are confined to these three species; and the crests for the rostral depressores are confined to B. imperator and vestitus, but they are generally rudimentary in the latter. The internal basal structure of the parietes is singularly like that of Chelonobia caretta, though there is no other special affinity to that genus. In the nature of basis; in the structure, to a certain limited extent, of the walls of the shell; in the narrowness of the carino-lateral compartments; in the elongation of the third pair of cirri; in the crests for the rostral and lateral scutal depressores, B. imperator comes nearer to the genus Tetraclita than does any other species of Balanus.

40. BALANUS FLOSCULUS. Pl. 8, fig. 5 a-5 f.

Shell purple or dirty white, with the internal basal edges of the parietes rough with irregular points and ridges; radii narrow or absent; basis excessively thin, in appearance absent. Scutum with crests for the lateral depressor muscle; tergum very narrow, with the spur pointed.

Var. sordidus. (Pl. 8, fig. 5 b) shell globulo-conical, dirty white, with numerous sharp, narrow, longitudinal folds or ridges.

Hab.--Peru and Chile; generally attached to the Concholepas Peruviana, or to Balanus psittacus, and associated with Chthamalus scabrosus. Var. sordidus, inhabits Tierra del Fuego, attached to littoral shells, wood, and rock, associated with Ch. scabrosus.

General Appearance.--Shell either extremely much depressed and irregular, or globulo-conical, or more rarely cylindrical and elongated. Walls, either with a few rather broad, smooth, irregular, longitudinal folds, or, in var. sordidus, with numerous sharper and more prominent longitudinal ridges; basal margin very sinuous. Colour, either fine rich peach-blossom purple, or so pale as to be almost white; or in var. sordidus dirty white, generally stained greenish from confervoid matter. Orifice small, oval, entire. Radii very narrow, white, or not at all developed, and with even the sutures not distinguishable. The purple coloured varieties, with the narrow white radii, the small oval orifice, and folded walls, have a very pretty appearance, which is far from the case with var. sordidus. The largest specimens attained a basal diameter of .6 of an inch, but this is an unusual size: I have seen a cylindrical specimen of var. sordidus one inch in length.

The opercular valves are united to the sheath by unusually strong membrane: internally, their upper parts are stained purple. Scuta, these vary considerably in breadth, some being even broader than in Pl. 8, fig. 5 c, and others as much elongated as in fig. 5 d: these latter come from an elongated cylindrical shell. The valve externally is unusually convex: the apex, also, projects freely to an unusual degree. Internally, the articular ridge is moderately prominent: the adductor ridge is prominent and much curved: in the upper part it either lies close to, or at some little distance from the articular ridge. The lateral depressores are attached to several little crests, occupying a cavity, (often bordered above by a little ridge) close beneath the adductor ridge. Tergum, extraordinarily narrow and elongated; beak triangular, purple: a longitudinal furrow runs down the valve: spur narrow, long, bluntly pointed, lying close to the basi-scutal angle of the valve: the scutal margin is nearly straight and parallel to the spur. Internally, the articular ridge is prominent: the crests for the depressores are moderately well developed: the upper part of the valve is marked by a purple patch, bounded on one side by the articular ridge, and on the other side by a very slight special ridge. There is some variability in the narrowness of the whole valve, and in the sharpness of the spur.

Parietes.--The under surface, in the more depressed varieties, is roughened in a remarkable manner nearly or quite up to the sheath, with very irregular, projecting, and branching ridges, and sometimes with depending points. These ridges and points are granulated on their under surfaces. The roughened surface in the more conical varieties is confined to the basal inner margin. This structure is nearly the same as that in B. imperator, represented (Pl. 8, fig. 4 c), but the little ridges are here more apt to be concentric, instead of radiating. The lateral edges of the compartments on the inside, especially the carinal edges, project inwards beyond the inner surface of the shell. The sheath is but little hollow on its under side. The diametric growth of the shell seems to be quite capricious; in the same group, some individuals thus increasing, and others not at all. When the radii are developed they are narrow and white, with their upper margins nearly if not quite parallel to the basis: their sutural edges are formed by large, irregular, branching teeth or septa. The alæ, also, have their sutural edges coarsely crenated; and when the shell increases by diametric growth, they are added to above the opercular membrane, so as to be nearly square at top.

Basis.--When a shell is removed from the surface of attachment, and inspected even under a lens, there appears to be no basis whatever, either adhering to the shell, or to the supporting surface: but when a more careful examination is made, with a higher power, an excessively thin, translucent, calcareous, irregular layer, or rather film, can almost always be discovered. This would be more easily distinguished if the specimens had adhered to rock instead of to the rugged shells of molluscs. At one time I thought the basis was partially membranous, for I have certainly scraped off small fragments of membrane from the supporting surface; but these, when examined under the compound microscope, seemed always to consist of a thin sheet of the yellow cementing tissue; and in some instances, a brittle film of shell, representing the true basis of the cirripede, still adhered to the upper surface of the membranous bits of cement. Nevertheless, so imperfect is the calcareous basis, that I should not be surprised if portions of a true membranous basis did really in some cases exist.

Mouth: labrum with the notch wide, generally with a few little teeth; mandibles with three teeth, and some inferior knobs; maxillæ notched. Cirri, first pair with one ramus shorter by three segments than the other ramus. Second and third pairs short, of nearly equal length, thickly clothed with spines; segments very little protuberant. Posterior cirri, having elongated segments, supporting seven pairs of spines.

Var. sordidus.--This form is very common on the tidal shores of the Strait of Magellan, and of the southernmost parts of Tierra del Fuego, near Cape Horn: it lives attached to rocks, mytili, and logs of wood, and is associated with Chthamalus scabrosus. It almost certainly is the most antarctic form of the genus Balanus. If I were guided by external appearance alone, I should certainly separate this form specifically from B. flosculus, but, as will be seen in the following description, the differences consist only in var. sordidus being much duller and rather differently coloured, in the longitudinal folds being sharper and more prominent, and in the whole shell being rather more globular, and on an average rather larger; but in the true B. flosculus there is considerable variation in all these respects, as there likewise is in var. sordidus; thus some of the cylindrical varieties of the latter have less prominent ridges than even B. flosculus. In general appearance I have seen some nearly, but not exactly, intermediate forms; therefore, I do not feel positive that these forms may not be specifically distinct, but have failed, after careful examination, to find any sufficient diagnostic characters. Moreover, in the case of Balanus lævis, I was led to believe that there is an equal and somewhat analogous amount of variation in the specimens inhabiting Tierra del Fuego and northern Chile; and in this case I was enabled to show the existence of strictly intermediate forms in the intermediate districts.

The shell in var. sordidus is generally globulo-conical, dirty white, frequently with a green tinge, from the growth of confervoid matter. Orifice small. The exterior surface is covered with numerous prominent, narrow, sharp ribs or folds, the basal margin being serrated with projecting points where the folds terminate. When the radii are not developed, the sutures are very often obscure. Internally, the shell is faintly tinted of a port-wine purple. In all points of structure this form is identical with the true B. flosculus. In some few specimens the whole exterior surface was disintegrated and smooth; and this is generally the case with the upper parts of the shell. Some other specimens, which had grown crowded together on wood, had become cylindrical, and consequently the orifice was as large in diameter as the shell, namely, half an inch: in some of these cylindrical varieties the sheath was entirely soldered to the walls. The largest specimens which I have seen were .6 of an inch in diameter; and above one inch in height.

Affinities.--This species, in its opercular valves, even in such trifling characters as the strength of the opercular membrane, and in its cirri, approaches closely to B. cariosus. We even see on the under side of the scutum, in that species, a single little ridge, foreshadowing, as it were, the crests for the lateral scutal depressores, so remarkable in our present species. In the structure of the shell and of the basis, B. flosculus is much more closely related to the last species, or B. imperator. If it had been possible to have arranged the species in a single line, B. flosculus ought undoubtedly to have been placed between B. cariosus and imperator.

41. BALANUS BISULCATUS. Pl. 8, fig. 6 a-6 c.

BALANUS SULCATINUS (?) Nyst, apud D'Omalius (sine descript. aut tabulâ), Geologie de Belgique, 1853.[100]

[100] I am indebted to M. Bosquet for a specimen, bearing this name and reference, found in the 'Systeme Bolderien' of Dumont, (miocene according to Sir C. Lyell) at Bolderberg. The specimen consists of a rostrum, with a portion of the base attached; and as these parts are in some degree characteristic, I fully believe this specimen to be the B. bisulcatus. I hope hereafter to give in the Palæontographical Series fuller illustrations of this and the following fossil species.

Radii with their upper margins oblique and smooth; sutural edges smooth: basis permeated by large pores. Scutum narrow, with from two to four longitudinal furrows: tergum with the spur very short, broad as half the valve.

Var. plicatus, with the walls deeply folded; radii narrow, with their upper margins very oblique.

Fossil in Coralline Crag, Ramsholt, Gedgrave, Sutton; Mus. S. Wood, Bowerbank, J. de C. Sowerby. Rauville, dans le Cotentin, Mus. G. B. Sowerby. Var. plicatus, Coralline Crag, Sutton, Mus. S. Wood. Bolderberg, near Hasselt, Belgium, Mus. Bosquet.

General Appearance.--Shell conical or tubulo-conical, often rather globose; walls frequently thin, either very smooth, or deeply plicated longitudinally: occasionally the same specimen is smooth in the upper part, and strongly plicated in the lower. The Radii in the larger specimens are wide, and with their upper margins only slightly oblique; in the smaller, they are narrower and much more oblique, but in each case their upper margins are smooth and slightly bowed. Colour apparently originally nearly white, but with the alæ generally, in the smaller specimens, clouded with a dark tint: the radii are usually striped feebly in longitudinal lines. Basal diameter of largest specimen .8 of an inch; but this seems to have been an unusual size.

Scuta: narrow, with the basal margin forming an unusually small angle with the occludent margin; surface slightly convex, with lines of growth approximate, moderately prominent; on the tergal half of the valve, two distinct rather broad furrows, with sometimes a third, and even a fourth, nearer to the occludent margin (Pl. 8, fig. 6 a), extend from the apex down the valve, and give it a very peculiar appearance: the furrows near the tergal margin are the deepest. Internally, the upper part of the valve is roughened with small points: the articular furrow is unusually wide: the articular ridge is very prominent and but little reflexed, with the lower end almost abruptly cut off: the adductor ridge is prominent, but short: there are small deepish pits for the rostral and lateral depressores.

Terga (6 b), broad, flat, with a slight narrow prominent rim along the scutal margin, which margin is slightly bowed. The basal margin on the carinal side of the spur slopes so gradually towards the spur, that the latter is barely distinct, and is very short, not depending nearly half its own width beneath the basi-scutal angle: it is broad, namely, measured across the upper part, as broad as half the valve; its basal end is obliquely rounded off on the carinal side; it is placed close to the basi-scutal angle. The carinal margin of the valve is just perceptibly bowed, and is formed by rectangularly upturned lines of growth. Internally, the upper part of the valve is rough; the articular ridge is prominent; the crests for the tergal depressor muscles are moderately well-developed.

Parietes, not porose; internally, the ribs are smooth, with their basal edges very finely or barely denticulated. The radii (as already stated) are of variable breadth; they have their upper margins either very slightly or highly oblique, but always smooth and rounded: their sutural edges are quite smooth, or sometimes, with a strong lens, traces of transverse striæ, representing septa, can just be discovered. The alæ have their upper margins very oblique; their sutural edges are, in the large specimens, quite smooth; in the younger ones, plainly crenated; the recipient furrow being clearly marked with these teeth. Basis plainly porose.

Varieties.--It is certain that there are longitudinally plicated specimens of this species, and that the obliquity of the upper margins of the radii also varies a little: nevertheless some of the deeply plicated specimens undoubtedly have a very different aspect from the ordinary varieties, and do really differ in the sutural edges of the alæ being crenated, and in the greater narrowness and obliquity of the radii; but these points are all commonly variable. I have not seen any large specimens of the variety, plicatus, so as to compare them with the large specimens of the normal form, yet I can hardly entertain any doubt, considering their agreement in so many important points, that I have rightly treated these forms as mere varieties; it is unfortunate that none of the specimens of the var. plicatus seen by me have had opercular valves, as their presence would have removed all shadow of doubt.

Affinities: this is a strongly characterised species, and nearly allied only to the following species, B. dolosus. The furrows on the scuta in some degree resemble those on B. lævis, but there is no alliance with that species. It is certain that amongst recent species, the chief affinity is with B. Hameri and amaryllis.

42. BALANUS DOLOSUS. Pl. 8, fig. 7.

Radii with their upper margins oblique and smooth; sutural edges smooth: basis permeated by large pores. Tergum with the spur not very short, broad as one third of valve.

Fossil in Red and Mammaliferous Crag, England; Mus. S. Wood, Bowerbank, Lyell, J. de C. Sowerby, Henslow, &c. Mammaliferous Crag, Postwick, near Norwich, Mus. Lyell.

This species so closely resembles B. bisulcatus, both externally and in all the essential characters of the parietes, radii, and basis, that it is quite superfluous to describe over again these parts. The specific characters are derived from the opercular valves, which present well defined distinctions, found by me constant in several specimens of both species. B. dolosus, like B. bisulcatus, has quite smooth and deeply plicated varieties, often adhering to the same univalve. The ribs on the inner surfaces of the parietes are remarkably prominent. I think the upper margins of the radii are in this species rather more oblique than in B. bisulcatus. The sutural edges of the radii are marked by the finest striæ, representing septa. The sutural edges of the alæ are generally distinctly crenated. The basis is often slightly cup-formed, and very plainly porose: its surface is marked by radiating ridges. The orifice of the shell is large, and elongated, especially in young specimens. The basal diameter of the largest specimen is .4 of an inch.

The Scuta have no trace of the two or three longitudinal furrows so conspicuous on these valves in B. bisulcatus, and which, in that species, run down from the apex of the valve; this fact showing that the furrows occur in quite young individuals. The whole valve is not quite so narrow as in B. bisulcatus, but otherwise agrees with it in shape: internally, there is hardly any difference: the articular furrow is not so wide: the articular ridge is very prominent, and abruptly truncated at its lower end: the adductor ridge is also prominent; it here runs a little higher up the valve than in B. bisulcatus. The Tergum differs more in the two species: the spur is not so broad; measured in its upper part, it is only about one third of the entire width of the valve, instead of being half as wide as the valve: it is considerably longer, depending beneath the basi-scutal angle more than half its own width: the basal margin of the valve on the carinal side, does not slope so gradually into the spur: the occludent and carinal margins are slightly arched, as in B. bisulcatus. Internally, the surface is rough, the articular ridge is prominent, and the crests for the tergal depressores are well developed,--all as in B. bisulcatus. It is remarkable, how generally the opercular valves have been preserved in this species in its fossil condition, as compared with most other species of the genus.

It is not easy to distinguish by external characters the rugged varieties of this species from B. crenatus; indeed, the only difference is that the furrows receiving the edges of the radii, generally, exhibit in B. crenatus a slight impression of the septa, which are entirely absent in B. dolosus. By internal characters, such as the non-porose parietes, and porose basis, our present species widely differs from B. crenatus.

43. BALANUS UNGUIFORMIS. Pl. 8, fig. 8 a-8 b.

BALANUS UNGUIFORMIS. J. de C. Sowerby (!). Mineral Conchology (sine descriptione) Tab. 648, fig. 1, (Jan. 1846).

---- ERISMA. J. de C. Sowerby (!). Ib., fig. 2.

---- PERPLEXUS. Nyst, apud D'Omalius (Sine descript. vel Tab.), Geologie de la Belgique, 1853.[101]

[101] I am much indebted to M. Bosquet for specimens bearing this title, from Klein Spauwen, which certainly appear to me, as far as can be judged by the separated compartments, without the opercular valves, to belong to our present species.

Parietes thin, sometimes permeated by pores; radii with their upper margins oblique; sutural edges very finely crenated: basis solid. Tergum with the spur narrow, bluntly pointed.

Var. erisma, with the walls longitudinally folded or ribbed.

Fossil in the Eocene formation, Isle of Wight, Colwell Bay; Hordwell; Barton, (Chama Bed); Headon; Bembridge. Bergh, near Klein Spauwen, Belgium (?). Attached to various shells and wood. Mus. J. de C. Sowerby, E. Forbes, F. Edwards, Charlsworth, T. Wright, Bowerbank, Tennant, Bosquet.

This species, the most ancient one as yet well known in the genus, presents to the systematist a most unfortunate peculiarity, in the parietes being almost as often as not permeated by small pores: I have seen no other instance, except to a limited degree in B. glandula, of this character being variable, and hence it must be still considered of high classificatory value, in so varying genus as Balanus. Owing to this varying condition of the parietes, together with the basis being quite solid, our present species has as good a claim to be ranked in the last as in the present section; indeed, I think it has more affinity to B. crenatus and glandula in the last section, than to any other recent forms: I have placed it in its present place, owing to its intimate affinity to B. varians, in which the parietes seem always to be solid; and partly, I believe, because all the first specimens examined by me exhibited no traces of parietal pores. Owing to the kindness of Mr. F. Edwards, I have seen the original specimens, excellently figured by Mr. J. de C. Sowerby in the 'Mineral Conchology:' I can perceive no difference between B. unguiformis and erisma, excepting that the walls in the latter are longitudinally folded,--a character we know to be variable in so many species. In both varieties, the parietes are sometimes porose and sometimes solid. The smaller specimens, however, figured in the 'Mineral Conchology' to the right hand, may possibly be a distinct species, as I infer from the narrowness of their radii.

General Appearance.--Shell, tubulo-conical, sometimes considerably elongated and sub-cylindrical: surface either very smooth, or slightly folded, or deeply folded so as to be strongly ribbed longitudinally: orifice rather large, rhomboidal, narrow at the carinal end, toothed, but not deeply: walls rather thin and fragile: radii of moderate width, with their summits oblique, not quite smooth. Basal diameter of largest specimen, about three quarters of an inch.

Scuta, with the external surface smooth: there is a trace of a furrow running down the valve from the apex, near to the occludent margin, and this is only worth mentioning from the analogous furrows in B. bisulcatus. Internally, the upper surface of the valve is roughened: the articular ridge is very prominent, and slightly reflexed: there is no distinct adductor ridge; there is a slight but variable depression for the lateral depressor. Tergum, with the longitudinal furrow shallow; spur moderately long, about one fourth or one fifth of the width of the valve; placed at about its own width from the basi-scutal angle; basal end bluntly pointed; the basal margin on the opposite sides of the spur forms a nearly straight line; the carinal margin has an extremely narrow border formed by upturned lines of growth. Internally, the surface is roughened with little points: the articular ridge is prominent: the crests for the tergal depressores moderately prominent.

Parietes: the longitudinal ribs on the internal surface are either feebly, or, in the lower part, strongly developed; their basal ends are only just perceptibly denticulated. As already stated, in about half the specimens, there were no traces of parietal pores; in the other half there were either distinct or obscure pores; the pores are circular, generally of unequal sizes, and never large; in the same individual they would sometimes be almost wholly absent in some of the compartments, and quite plain in the other compartments. The Radii are either moderately wide or rather narrow, and have their upper margins very oblique, and not distinctly arched, and not quite smooth: their sutural edges are very finely crenated, the teeth or septa not being denticulated. The upper margins of the alæ are rather less oblique than those of the radii: their sutural edges are barely crenated. The basis is thin, and without any trace of pores; the upper surface is sometimes furrowed in radiating lines.

44. BALANUS VARIANS. Pl. 8, fig. 9.

B. VARIANS. G. B. Sowerby, in Darwin's Geolog. Observ. on South America, (Sept. 1846), Tab. 2, fig. 4, 5, 6.

Parietes moderately thick: radii with their upper margins very oblique; sutural edges almost smooth, or finely crenated: basis finely porose. Tergum with the spur small, narrow, bluntly pointed.

Hab.--Port St. Julians, Patagonia; ancient Tertiary formation. Eastern plain of Tierra del Fuego (?).

This species comes so close to B. unguiformis, that I have some doubt whether they ought to be specifically separated: the whole shell is stronger, and the basis can be seen to be porose when a polished section is made: the spur of the tergum is smaller, more pointed and more medial, but these latter differences may be due to mere variation. Should B. varians and unguiformis prove to be the same species, the latter name has the priority.

General Appearance.--Shell moderately strong and thick; shape conical or tubular, or even inverted conical; orifice moderately toothed, large, sub-trigonal; walls either smooth or longitudinally folded; the elongated specimens are most apt to be smooth. The Radii are narrow and oblique. Diameter of largest specimen above three-quarters of an inch.

Scuta, with the lines of growth moderately prominent; the internal surface of the valve has been ill preserved; but a very prominent, hardly reflexed, articular ridge, can be distinguished, as well as the absence of an adductor ridge. Terga, with no distinct longitudinal furrow running down the valve: spur short, bluntly pointed, narrow, about one fifth or one sixth of width of valve; placed at above its own with from the basi-scutal angle; the basal margin, on each side close to the spur, curves towards it. Internally, all that can be distinguished, is that the articular ridge is prominent.

Parietes; their inner surfaces appear to have been nearly smooth; the absence of parietal pores could be made out only by polishing a transverse section. The Radii are narrow, and have their upper margins very oblique and rather smooth: in the elongated varieties the sutural edge appears to be almost absolutely smooth; in the conical specimens it is slightly crenated, the septa being apparently not denticulated. In living species we have a similar variation in the state of the sutural edges of the radii, in B. balanoides and crenatus the edges being much smoother in much elongated specimens than in other varieties. The alæ have their upper margins less oblique than those of the radii, with their sutural edges barely crenated. The basis is either flat, or, in the elongated specimens, deeply cup-formed; in section it can be seen to be finely and irregularly porose.

45. BALANUS INCLUSUS. Pl. 8, fig. 10 a-10 c.

Shell reddish-brown: radii broad, with their upper margins not oblique, or only moderately oblique; sutural edges with plainly denticulated septa: basis porose. Scutum without an adductor ridge; tergum with the spur rather narrow.

Var. (a) (Pl. 8, fig. 10 b, 10 c), with the shell elongated in its rostro-carinal axis; basis narrow, clasping the stem of a zoophyte; lateral compartments much broader than the almost linear rostrum, carina, and carino-lateral compartments.

Var. (b), with rough longitudinally folded walls, and with the summits of the radii forming an angle of about 45° with the basis.

Fossil in Coralline Crag, Sutton and Gedgrave; attached to foliaceous Bryozoa; Mus. S. Wood, Bowerbank. Var. a, Coralline Crag, Sutton, attached to cylindrical branches of corals; Mus. S. Wood. Var. b, attached to shells, Osnabruck, Hanover, Mus. Lyell; Bünde, Westphalia, Mus. Krantz.

My materials consist of a beautiful series of specimens in Messrs. Wood and Bowerbank's collections; but unfortunately only a single young specimen had its opercular valves preserved. Not one specimen of the very curious variety (a) had opercular valves, yet I cannot feel any doubt about its being only a variety, caused by its attachment to a thin cylindrical branch of a coral, instead of to a foliaceous Bryozoon; it will, however, be convenient to give a separate description of this very remarkable form. With respect to var. (b), both sets of specimens came to me with the name B. stellaris, of Bronn; but as Bronn distinctly states, that in his species the parietes are porose, and as such is not here the case, this cannot possibly be that species: these specimens did not possess their opercular valves, and therefore cannot be identified with certainty.

General Appearance.--Shell conical, with the orifice rather large, and rhomboidal. The surface is very smooth, except in var. (b.) from the Continent, in which it is rugged and longitudinally folded. The colour is ochreous-brown (chiefly no doubt derived from the imbedding substance) tinged with red. The radii often have a much darker and more distinct red tint; they are sometimes longitudinally striped with dirty white. The radii are broad, with their summits straight, and very slightly oblique; in var. b, however, they slope at an angle of about 45°. Basal diameter of largest specimens .6 of an inch; but this is an unusual size.

Scuta (from a young individual), with the growth ridges little prominent. Internally the articular ridge is moderately prominent, with its lower end very obliquely rounded off; there is no adductor ridge; there is a minute pit for the lateral depressor muscle. Terga, with a slight longitudinal depression extending down to the spur: spur short, with its lower end almost square or truncated, about one fourth of width of valve, and placed at about half its own width from the basi-scutal angle. Internally, the articular ridge is prominent; the crests for the tergal depressores are feebly developed.

Parietes, moderately thick and generally strongly ribbed internally, without parietal pores. Radii, wide, with their upper margins straight, not smooth or rounded, and very slightly (or, in var. b moderately) oblique; their sutural edges have well-developed septa, which are denticulated: the interspaces between the septa are filled up solidly. The alæ have their upper margins oblique: they are only slightly, and sometimes not at all, added to above the level of the opercular membrane: their sutural edges are smooth. The basis is thin, but plainly porose.

Var. (a).--With respect to this remarkable variety, any one would at first think it specifically distinct. The shell is much compressed, or elongated in the rostro-carinal axis, sometimes to a great degree; I have seen a specimen .25 of an inch in this axis and only .1 in its broadest part; but this is a very unusual degree of elongation. The most remarkable character is the extraordinary narrowness of the carina, the carino-lateral compartments, and of the rostrum, compared with the great breadth, especially along the basal margin (Pl. 8, fig. 10 b, 10 c), of the lateral compartments. The radii are of unusual breadth. The tips of the rostrum and of the lateral compartments are a little arched in, tending to make the shell somewhat globular. The true basis is extremely narrow (fig. 10 c): it is deeply grooved, from clasping the thin, cylindrical stem of the coral to which it had adhered; and I have seen specimens in which the opposite edges of the groove had met, a tube having been thus actually formed. From the grooved basis, and from the elongation of the shell in the rostro-carinal axis, this species presents so close a general resemblance to Balanus calceolus, and its allies, that I have seen it in a collection arranged on the same tablet with a fossil specimen of B. calceolus. Notwithstanding the above several strongly-marked characters, by which this variety differs from the ordinary form, there is a resemblance in colour and aspect, which though difficult to be described, made me from the first suspect that the two were specifically identical. In no point of real structure is there any difference, excepting that, perhaps, the pores in the basis are here rather smaller; but this might arise from the little development of the peculiar basis. Having come to this conclusion, I was interested by finding a specimen in Mr. Wood's collection, which had originally fixed itself (judging from the form of the basis) on a cylindrical stem, but which had subsequently grown on to an adjoining flat surface; consequently, one side of the shell presented all the peculiar characters of the present variety, whereas the other side, at the rostral end, was undistinguishable from the ordinary form. The unequal development of the rostrum on the two sides was very striking, and clearly showed how great an effect could be produced by the nature of the surface of attachment.

This singular variety cannot be considered accidental, in the sense in which this term may be applied to some varieties: the larva evidently fixes itself intentionally, in a certain definite position, on the branch of the coral (when a branch is chosen), exactly as in the case of Balanus calceolus, or Scalpellum vulgare. But when other species of Balani occasionally fix themselves on branched corals, their position seems to be accidental and unsymmetrical; thus among the symmetrically elongated specimens of the present species, I found one specimen of Balanus bisulcatus, which had evidently been attached in an almost transverse position to a branch, and had thus become much distorted; so, again, I have seen specimens of the recent B. amaryllis attached irregularly to a Gorgonia, in the midst of the symmetrically elongated shells of Balanus navicula, an ally of B. calceolus.

This variety does not seem to attain so large a size as the ordinary form.

Affinities.--This species is allied to the two last described fossils, namely, B. varians and unguiformis, but is perhaps more nearly related to the recent B. allium, an inhabitant of the Barrier Reef of Australia. The longitudinally folded variety (b) can hardly be distinguished by external aspect, or even by the opercular valves, from B. crenatus; but when the shell is disarticulated, the porose walls and non-porose basis of B. crenatus, allow of no mistake in the diagnosis of the two species.

2. Sub-Genus--ACASTA. Pl. 9.

ACASTA. Leach. Journal de Physique, tom. lxxxv, 1817.

Compartments six; parietes and basis non-porose: basis calcareous, cup-formed, not elongated, attached to sponges, or rarely to the bark of Isis.

Distribution mundane; imbedded in sponges and the sponge-like bark of Isis.

This sub-genus, in one sense, is a very natural one, inasmuch as all the species are closely allied in essential structure, in general appearance, and in habit. On the other hand, in the structure of the shell, in all the characters derived from the opercular valves and animal's body, Acasta cannot properly be distinguished generically from some species of Balanus; thus B. navicula and cymbiformis agree in the parietes and basis not being porose and in all other essential respects, differing only in the shell being more elongated in the rostro-carinal axis and in being attached to Gorgoniæ instead of to sponges; yet we shall see that Acasta purpurata lives imbedded in the bark of Isis, so that even the habit of being imbedded in sponges fails. Balanus terebratus would have been ranked as an Acasta had it inhabited sponges. On the other hand, some species of Balanus inhabit sponges, as is often the case with B. spongicola, and always with B. declivis: but both these species are distinguished easily from Acasta, the former by its porose walls and basis, and the latter by its membranous basis; it may, however, be reasonably doubted whether such differences ought to be considered as even sub-generic. The most important character of Acasta probably consists in the anterior ramus of the fourth pair of cirri, differing slightly in the arrangement of its spines, and in some other points, from the rami of the two posterior pairs of cirri,--a character not as yet observed in any other cirripede. Had not the genus Acasta been already founded and extensively admitted, certainly I should not have formed it; but considering the close similarity in habits, aspect, and structure, of the nine species of Acasta, and considering the already large size of the genus Balanus, I hope I may stand excused for admitting Acasta as a sub-genus.

General Appearance.--The shape varies from nearly globular to that of a somewhat flattened acorn, the orifice being often a little contracted from the inward curvature of the tips of the parietes. In A. spongites, however, the orifice is generally widely open; and, on the other hand, in A. sporillus, the orifice is reduced to a mere pore. The usual tint is pale reddish, but A. purpurata is purple, and A. sporillus purplish-brown. The surface is either smooth, or is shagreened with minute points, as in A. sporillus, and fenestrata, and in some specimens of A. sulcata; and in all the species, except A. sporillus and fenestrata, many individuals are furnished with elongated, curved, sharp, shelly points, like those in var. spinosus of Balanus tintinnabulum. The summits of the radii, which are generally of moderate breadth, are more or less oblique; their surface is often marked by lines parallel to the basis, instead of by vertical lines corresponding with the lines of growth, as in most species of Balanus. The carino-lateral compartments vary in proportional breadth in the different species: in A. sporillus, they tend to become rudimentary, and in this species (Pl. 9, fig. 9 b) their basal margins, or rather points, do not reach down to the basis. The species are all small, A. glans and undulata are the largest, being sometimes .55 of an inch in basal diameter.

Opercular Valves.--These differ in no generic respect from those of Balanus. The Scuta are striated longitudinally in several of the species: the adductor ridge is barely developed in any, being most prominent in A. cyathus. The articular ridge is prominent in A. fenestrata and purpurata. In the Terga, the spur is either truncated and very broad, or moderately narrow and bluntly pointed: the surface of the valve is often depressed, and in A. spongites and fenestrata it is furrowed in the line of the spur. The articular ridge and furrow are well developed in A. fenestrata and purpurata. The crests for the tergal depressor muscles are either absent or very feebly developed.

Structure of the Parietes and Radii.--The parietes are not porose; internally, they are either smooth, or slightly, or strongly ribbed in longitudinal lines; the presence of these ribs, which are homologous with the parietal septa in Balanus, is variable even in the same species. In A. sporillus the inner surface is curiously reticulated. The sutural edges of the radii are either smooth, or very slightly crenated by the septa, in lines parallel to the basis. The upper margins of both radii and alæ are always more or less oblique. The radii sometimes do not extend down to the basis; and in this case, as will presently be described, apertures are left in the lower half, between the compartments. In A. glans and lævigata the internal margin of the wall of each compartment, from the sheath to the basis, projects inwards, forming inside the shell as many double ridges (Pl. 9, fig. 5 b), as there are compartments, namely, six: a nearly analogous structure occurs in certain species of Balanus. The basal edge of the sheath, in most of the species (5 b, 9 b), depends freely, and is hollow beneath, but this is always a variable point.

Basis.--The base is either saucer or cup-shaped, but in A. cyathus it is almost flat; it is generally symmetrical and smooth, with the lines of growth closely approximate. In A. fenestrata the basis is commonly as deep, as the shell is high. The edge, in several of the species, is crenated with minute teeth or notches; and these are so large in some specimens of A. sulcata and cyathus, as to make the edge almost pectinated. In A. glans, and in a lesser degree in A. lævigata, there are six knob-like teeth (fig. 5 a), corresponding with the points of junction, between the basal edges of the inwardly prominent margins of the six compartments, and the basis: in those specimens, in which the six teeth are largely developed, six ridges produced by their successive development, extend down towards the centre of the basal cup. When the basal cup is dissolved in acid, there is but a little animalised tissue and an external membrane, formed as usual in slips, and furnished with blunt little external points (apparently representing spines), each of which has a short tubulus extending to the corium. Although I dissolved the basis of three specimens, I could not distinctly make out any cement; nor did I see any cement-ducts; yet these are readily distinguished, after the dissolution of the basis in acid, in Balanus, Elminius and Tetraclita. There can be no doubt that the young shell must at first be cemented to a fibre of the sponge; but I suspect that the cementing-tissue is not subsequently formed, owing to the support afforded by the growth of the enveloping sponge. As some species of Balanus are habitually or occasionally imbedded in sponges, it is important to observe, that the species of Acasta are not only imbedded, but are attached to the fibres of the sponge: but even this character, as we have already seen, is not sufficient to distinguish the genus Acasta from Balanus, for B. declivis is attached exclusively to sponge.

Perforations in the Shell.--Calcification seems often to fail to a certain extent in this genus: the basal cup in most specimens of A. spongites, and in some of A. glans and other species, is irregularly perforated by numerous minute orifices, closed only by the external membrane, and filled up inside by pulpy corium. In some specimens of A. spongites, from the Cape of Good Hope, parts of the basis were riddled like a sieve. I have seen similar perforations in the parietes of a few specimens of A. glans. In some specimens of A. sulcata, the radii do not extend quite down to the basal edge of the walls (Pl. 9, fig. 2 a), and in consequence a small cleft, closed only by membrane, is left between the compartments, for a little space above the basal cup. In A. fenestrata (fig. 7 a), and in a lesser degree in A. purpurata (8 a), not only do the radii not extend to the basal cup, but the parietes either on one or both sides of each suture are hollowed out, so that six, large or small, elongated, membrane-covered openings are formed, which extend from beneath the sheath down to the basal cup. These openings, which I have not seen in any other genus, will be more fully described under the respective species.

Mouth.--The parts of the mouth are identical in the several species, and present no generic differences from those in Balanus. The outer maxillæ and palpi appear unusually prominent: the labrum is deeply notched, with no teeth, or very obscure teeth on each side. The mandibles have five teeth, but the fifth is sometimes confluent with the inferior angle. The maxillæ are not notched; and carry one or two spines, near their inferior angle, nearly as large as the upper pair. The outer maxillæ are bilobed.

Cirri: in the first pair, the rami are very unequal in length, the one ramus being from half to one-third of the length of the other. The segments in the second and third pairs, are not so much broader, or so much more crowded with bristles, in comparison with the three posterior pairs, as is the case with most species of Balanus. The three posterior pairs, except in A. purpurata, are much elongated, and the long thin segments bear four, and sometimes only three, pairs of spines, which are generally doubly and finely serrated, or even feathered. The most remarkable fact respecting the cirri, is, that in A. spongites, sulcata, cyathus, and glans, the fourth pair, instead of being identical in structure, as in all other genera, with the fifth and sixth pairs, has, on its anterior ramus, the pairs of spines more crowded together, with the little intermediate spines, and those in the dorsal tufts, a little longer than in the sixth cirrus; and between the pairs of spines, there occur some straight, upwardly pointed, very minute, and very thick spines or teeth. And, what is still more remarkable (as will hereafter be described in detail), in certain specimens, but not in all, of A. sulcata, the front surfaces of the lower segments on the anterior ramus, are developed into thick, small, downwardly curved, hook-like teeth; this likewise is the case with the upper segment of the pedicel (Pl. 29, fig. 2),--a most elegant, mandible-like organ for the prehension of prey being thus formed. The variability of such beautifully contrived teeth is very surprising. Some similar teeth occur on the segments of the anterior ramus of the fourth cirrus, but not on the pedicel, in A. cyathus. A few teeth resembling the above, but thicker, occur on the segments of the anterior ramus of the same cirrus, in A. purpurata.

Branchiæ, &c.--In A. spongites, I found the branchiæ rather small, with transverse plications. The muscles of the sack, which run to the opercular valves, seemed rather feeble in most of the species. The penis in several species was remarkably long, and in A. spongites I noticed the straight projecting point at its dorsal base, as is common in Balanus.

Affinities, &c.--At the commencement of the description of the genus, I gave my reasons for keeping Acasta distinct as a sub-genus from Balanus. The species are particularly troublesome to identify, not only from the great variability of the most obvious characters, but from the very close general external appearance of most of the species, and the consequent necessity for cleaning and disarticulating at least one specimen in every group. The shape, however, of the shell and basis, and the state of their disarticulated edges, whether smooth, crenated, or toothed, here offer more serviceable, though still very variable, characters for the identification of the species, than is usual with sessile cirripedes; and this, probably, is in part due to the almost free or unattached condition of the whole shell, suspended, as it were, in the midst of sponges, which they inhabit. The opercular valves, on the other hand, are less serviceable than usual.

Range, Habitats, &c.--The species are found all over the world, excepting in the very cold latitudes.[102] Acasta lævigata ranges from the Red Sea to the Philippines; A. spongites from the south of England and Wales to the Cape of Good Hope; and A. cyathus from Madeira to the West Indies; most of the other species seem to have rather confined ranges. The East Indian Archipelago seems to be the metropolis of the genus, for here A. lævigata, fenestrata, purpurata, and sporillus, are all found. Of these four species, A. purpurata lives imbedded, not in sponges, but in the sponge-like bark of an Isis; and I think it probable, that A. sporillus may have somewhat analogous habits. The same species often lives imbedded in different kinds of sponge; thus, I have seen A. lævigata and cyathus in apparently three kinds, and A. spongites in, as I believe, four kinds. The genus existed during the miocene period, in the Coralline Crag, under a form closely allied to A. spongites.

[102] I am greatly indebted to Mr. Bowerbank for his great kindness, in looking over his immense collection of sponges from all parts of the world, and sending to me all the specimens of Acasta he could find imbedded in them.

1. ACASTA SPONGITES. Pl. 9, fig. 1 a-1 d.

LEPAS SPONGITES. Poli. Testacea utriusque Siciliæ, 1795, Tab. 6, fig. 3-6.

BALANUS SPONGEOSUS. Montagu. Test. Brit. Suppl., 1808.

---- SPONGITES. De Blainville. Dict. Sc. Nat., Pl. 116, fig. 3.

LEPAS SPONGIOSA. Wood's General Conchology, p. 47.

ACASTA MONTAGUI. Leach, in Lamarck, Animaux sans Vertèbres, 1818, et in Encyclop. Brit., Supplement, 1824, vol. 3, Pl. 57.[103]

---- ---- J. E. Gray. Annals of Philosophy, New Series, vol. 10, Aug. 1825.

---- SPONGITES. Philippi. Enum. Mollus. Siciliæ, vol. 2, p. 211, 1844.

BALANUS MONTAGUI. Brown's Illustrations of Conchology (2d edit. 1844), Pl. 53, fig. 24-26.

[103] As the plate to the Supplement to the 'Encyclop. Brit.' is marked as engraved in 1817, I presume Dr. Leach gave a proof to Lamarck, thus enabling him to publish this species four years before the Supplement itself appeared.

Carino-lateral parietes about one sixth of width of lateral parietes: inner surface of the parietes generally ribbed feebly: scutum with the articular ridge abruptly cut off at its lower end: tergum with the spur rounded-truncated, about one third of width of valve.

Hab.--South coast of England; South Wales, (Tenby); Portugal; Naples; Sicily; Cape of Good Hope.

This species and the three following, have caused me much doubt and trouble. At first I took the view here adopted, namely, that they were distinct: more careful examination made me run them altogether under one name. Finally, after still further deliberation, and the examination of a few additional specimens, I concluded there was the least chance of error in classing them separately. I may here mention, that in some sponge from the Cape of Good Hope, this species was mingled with Balanus spongicola.

General Appearance.--The shape is usually that of a cup, the orifice being, in most cases, rather large, and deeply notched, owing to the great obliquity of the radii and alæ. The surface is generally smooth, but furnished with sharp calcareous projections. The colour is pinkish, and chiefly in the upper part of the shell; the lower part is often yellowish from the preserved epidermis. The parietes in the carino-lateral compartments are always narrow, being only one sixth or one seventh of the width of the parietes in the lateral compartments. The radii are not very wide, never equalling in width the parietes. The basis is moderately deep, and sometimes very deep, being even occasionally curled like a horn on one side. The specimens from Lisbon and Naples are a little larger than any British specimen which I have seen; the former being .3 of an inch in basal diameter.

Scuta: these are striated longitudinally in close lines, generally plainly, but to a variable degree. The whole valve is flat, thin, and rather elongated, with barely a trace of an adductor ridge: the articular ridge is short and rather prominent: it terminates downwards abruptly, and this does not appear to be the case in the two following species. Terga: these are small compared with the scuta, they are slightly beaked: the spur is truncated but rounded, more especially on the carinal side; it is rather more than one third of the width of the whole valve. The articular ridge and crests for the depressor muscles are feebly developed.

Structure of the Parietes and Radii.--The state of the inner surface of the parietes varies much; generally they are slightly ribbed close to the basis, the ribs sometimes extending up to the sheath; rarely the surface is quite smooth. The edges of the radii are slightly crenated. The upper internal surfaces of the radii, where overlying the alæ, are usually marked by feeble undulating lines, nearly parallel to the basis. The alæ have very oblique summits.

Basis: this is generally of a regular cup-like form, and about two thirds as deep as the shell is high; sometimes it is pointed at the bottom and distorted. The edge is feebly crenated, and rarely quite smooth. It is often penetrated by small rounded irregular holes; and I have seen specimens from the Cape of Good Hope with parts like a sieve.

Cirri: in the first pair, the anterior ramus is nearly thrice as long as the posterior ramus. The second cirrus is short, with one ramus longer by three or four segments than the other ramus; the terminal segments are truncated. The third cirrus is about one third longer than the second cirrus. In the anterior ramus of the fourth pair, the regular pairs of spines are rather crowded together in the upper part of each segment, and the intermediate little spines and dorsal tufts are rather long in comparison with those of the fifth and sixth pairs of cirri: moreover, amongst the regular pairs, a few very minute and thick spines, pointing upwards, could be perceived. So that we here have the very unusual case of the fourth cirrus not exactly resembling the fifth and sixth pairs; and we shall see, in the following species, that this same anterior ramus of the fourth cirrus presents in addition another very extraordinary character. In the sixth cirrus there are on each segment four pairs of spines.

2. ACASTA SULCATA. Pl. 9, fig. 2 a-2 d.

ACASTA SULCATA. Lamarck. Animaux sans Vertèbres, 1818.

---- ---- Deshayes, in Guerin, Magasin de Zoologie, 1831, Tab. 24.

Carino-lateral parietes about one sixth of width of lateral parietes: inner surface of the parietes generally ribbed strongly: basis with the edge strongly crenated: orifice of shell rather small: tergum with the spur generally truncated and nearly half as wide as valve.

Var. (a) (fig. 2 b): with the walls externally ribbed.

Var. (b) (fig. 2 a): with small membrane-covered clefts between the edges of the walls, close above the basal cup.

Hab.--Sydney, Port Fairy, Moreton Bay in lat. 27° S., New South Wales; Southern Australia; and, according to Lamarck, Western Australia, in lat. 25° S. Mus. Brit., Cuming, Bowerbank, &c.

I am almost ashamed to admit this species, so small are its differences compared with A. spongites; yet I think that it probably is a distinct form.

In general appearance and character this species comes very near to A. spongites. As in the latter, the parietes of the carino-lateral compartments are narrow.[104] The orifice seems always to be smaller. Internally, the parietes are generally much more strongly ribbed, and the edges of the basal cup more plainly crenated. The sheath is generally coloured of a brighter pink, sometimes tinged with orange. The average largest specimens (from .3 to .5 of an inch in basal diameter) are a little larger than the largest European specimens: I have seen one specimen from Moreton Bay .4 in basal diameter, and from the basal cup being very deep, actually .75 in height. The scutum has the articular ridge not so prominent and not so abruptly cut off at the lower end, as in A. spongites: on the other hand, the adductor ridge seems rather more prominent; but these differences are trifling. In the tergum the breadth of the spur (fig. 2 c, 2 d) varies in specimens taken out of the same branch of sponge; some can hardly be distinguished from the same valves in A. spongites, but generally the spur is broader and squarer.

[104] In Mr. Cuming's collection there is a specimen, from Sydney, which I fully believe to be the present species, but cannot be positively sure, as the opercular valves have been lost, which is very remarkable from the walls of the carino-lateral compartments being reduced to the thickness of a mere thread, not one twentieth of the width of the lateral compartments; we here see the structure of Acasta sporillus prefigured.

This species presents some remarkable varieties: in one specimen, from Sydney, the parietes were externally ribbed longitudinally (fig. 2 b), the ribs being roughened with minute points, giving to the shell an elegant appearance; and this without doubt is the A. sulcata of Lamarck, procured by Peron at Shark's Bay, lat. 25° S., on the opposite of the Australian continent: some specimens from Port Lincoln, in South Australia, were not ribbed, only smoothly striated in longitudinal lines; although both sets of specimens had almost smooth scuta, and were thus different from common specimens, yet there could be no doubt, from their similarity in all other points, that they did not differ specifically from them, though the latter had their scuta striated, but not their parietes. Hence we see that there is no relation between the striæ on the parietes and on the scuta. The Port Lincoln specimens, and some others, were remarkable from the radii not extending down to the basal cup, a minute cleft, covered only by membrane, being thus left along the sutures, low down between the parietes (fig. 2 a); we shall see this singular structure strongly developed in A. perforata. Owing apparently to these clefts, the edge of the basal cup, exhibited traces of six knob-like teeth, like those characteristic of A. glans.

Cirri.--The cirri resemble those of A. spongites, with the exception that the segments on the posterior pairs bear only three main pairs of spines. With respect to the anterior ramus of the fourth pair of cirri, the following very singular facts were observed:--in a specimen from New South Wales (var. with the tergum having a narrow spur), on two or three of the lower, but not on the lowest, segments, the front margin was produced or developed into two or three minute, thick teeth, slightly curved like hooks downwards: in other specimens from New South Wales (var. with the tergum having a broad spur, and inhabiting the same branch of sponge with the last-mentioned variety), there was no trace of these teeth. But again, in two other specimens with the tergum having a broad spur (collected by different persons, near Sydney), and in another from South Australia, this structure was carried to an extreme, for in these (as represented, Pl. 29, fig. 2) there were beautifully formed teeth on the fourteen lower segments (the twelve upper being without them), and likewise on the upper segment of the pedicel. These teeth are graduated in size on each segment; they are admirably adapted for securing any prey; and, in fact, they convert each segment into a mandible-like organ. On the segments, on which these teeth are well developed, some of the regular pairs of spines are aborted.

Diagnosis.--Finally, this species, if it be, as I believe, distinct, differs from A. spongites only in the internal surface of the parietes being more strongly ribbed and brighter coloured,--in the edge of the basal cup being more plainly crenated,--in the articular ridge of the scutum being of a different shape,--in the spur of the tergum being often broader,--in the segments of the posterior cirri having only three pairs of main spines,--and, lastly, in the occasional presence of the hook-like teeth on the anterior ramus of the fourth cirrus.

3. ACASTA CYATHUS. Pl. 9, fig. 3 a-3 c.

Carino-lateral parietes about one fourth of width of lateral parietes: radii wider than the parietes: basis nearly flat, small: tergum with the spur truncated, half as wide as valve.

Hab.--Madeira, Mus. Lowe, and Bowerbank. West Indies, Mus. Stutchbury. Hab. unknown, Mus. Brit.

I feel more confidence in this case, than in that of A. sulcata, that we here have a distinct species, though at one time I treated it only as a marked variety of A. spongites. I rely chiefly on the great proportional width of the radii of all the compartments, and on the width of the carino-lateral compartments, compared with the lateral compartments, and on the general shape of the shell, which differs considerably from that of the two previous forms: in consequence of Acasta being attached to and imbedded in a yielding substance, such as sponge, I believe external form to be of more value as a specific character in this genus, than in most sessile cirripedes. I have examined specimens taken out of the yielding Spongia officinalis and out of an unusually compact sponge, and they resembled each other in every respect.

General Appearance.--Colour pale pink, or that of flesh: basis remarkably flat and rather small, with the walls above bulging out a little. The radii are very wide, being wider than the parietes to which they belong: the orifice is generally rather large. The parietes of the carino-lateral compartments vary from one third to one fourth of the width of the parietes of the lateral compartments. Basal diameter of largest specimen .35 of an inch. Internally, the parietes are generally more strongly ribbed than in A. spongites.

The Opercular Valves are large, owing to the form of the shell. The Scuta present no particular character, and are not distinguishable from those of A. sulcata; but the adductor ridge is perhaps rather more developed. The Terga (Pl. 9, fig. 3 c) are nearly as large as the scuta, and this is an unusual circumstance; the spur is more than half as wide as the valve; it is placed not quite close to the basi-scutal angle; on the carinal side, the basal margin of the valve slopes a little towards the spur. I may mention, that in several specimens from Madeira, the scuta and terga, on one side, had grown to a monstrous thickness.

Cirri: these resemble, in every respect, those of A. spongites, with the remarkable exception that on the anterior ramus of the fourth cirrus, several segments were furnished with the beautiful downward curved, mandible-like teeth, as in A. sulcata; but differently from in that species, there were none on the upper segment of the pedicel. I should have thought this an excellent specific character, had not these teeth been so extremely variable in A. sulcata.

Finally, I think this species is more nearly related to A. sulcata than to A. spongites.

4. ACASTA UNDULATA. Pl. 9, fig. 4.

Shell, apparently, as in A. spongites, but larger: scutum marked by longitudinal ridges, often in pairs, with the intermediate furrows rather wide: spur of tergum nearly half as wide as valve.

Fossil in Coralline Crag (Sutton), Mus. S. Wood.

I owe to Mr. Wood the inspection of a fine suite of separate valves. Owing to the shell never having been found entire, its general shape is not known, and, what is of more consequence, the relative proportional width of the parietes of the carino-lateral compartment is unknown. I have (but with doubt) given it a distinct specific name, owing to the peculiar character of the furrows on the scuta, and to the large size of the whole shell. In its other characters it comes nearest to A. spongites, excepting in the spur of the tergum, which resembles that of A. sulcata.

The compartments appear to have been rather smooth externally. The radii are not wide, as in A. cyathus; and the basis is cup-formed. Internally, the parietes are feebly ribbed, as in A. spongites. Judging from the dimensions of the separated valves, this species must have equalled and perhaps exceeded the size of the largest living species, namely, A. glans, from Australia. Hence we may infer, that the basal diameter probably exceeded .55 of an inch: I may add, that the largest European specimens of A. spongites, from Naples and Portugal, are only .3 of an inch in basal diameter.

Scuta.--These seem to resemble the scuta of A. spongites in all respects, except in the longitudinal ridges standing much further apart, and, consequently, in the furrows being much wider: each ridge is generally double. Although there is a good deal of variability in the character of these ridges in A. undulata, and likewise in A. spongites, I have not seen any form intermediate between them. It must, however, be confessed, that this is an extremely variable character in many sessile cirripedes. In the Terga, the spur is about half the width of the whole valve, and therefore rather wider than in A. spongites.

5. ACASTA GLANS. Pl. 9, fig. 5 a-5 c.

ACASTA GLANS. Lamarck. Animaux sans Vertèbres, 1818.

Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge rarely crenated, but furnished with six inwardly prominent teeth: scutum strongly striated longitudinally.

Var. (a) with the edge of the basal cup finely crenated.

Hab.--New South Wales, Southern Australia; Mus. Brit., Stutchbury, &c.

This fine species seems to be extremely common, imbedded in an open porose sponge on the eastern and southern shores of Australia. It is very distinct from the other species, with the exception of the following A. lævigata, which, with some hesitation, I have allowed to remain specifically separated.

General Appearance.--Excepting in its larger size, this species differs in external appearance but little from A. spongites; its colour is pale dirty reddish. The surface is generally studded with small calcareous points. The parietes of the carino-lateral compartments are about one fourth of the width of the parietes of the lateral compartments, and therefore proportionally of the same width as in A. cyathus. The largest specimen which I have seen, was .55 of an inch in basal diameter.

Scuta.--These are slightly narrower, thicker, and more convex than in A. spongites: they are strongly striated in longitudinal lines. The articular ridge is very feebly developed. Terga: in full-grown specimens, the spur is half the width of the whole valve, and is truncated; its basal edge being parallel to the basal margin of the valve. The articular ridge and crests for the depressor muscles are very feebly developed.

Internal structure of the parietes.--The inner surface of the parietes is quite smooth, without even a trace of ribs or teeth. But the most important character is that the internal lateral margins on both sides of each compartment, from the sheath to the basis, project inwards and form a rim; so that when the shell is viewed from within (Pl. 9, fig. 5 b, representing the lateral and carino-lateral compartments, and part of the carina), the six sutures are seen to be strengthened by six double columns.

Basis.--This is moderately cup-formed. The edge, in order to meet the basal points of the inwardly projecting lateral margins of the six compartments, has six knob-like teeth. These are placed at unequal distances, for two on each side stand near each other, owing to the narrowness of the carino-lateral compartments. The degree of their development varies extremely; when most developed, as in the specimen figured (Pl. 9, fig. 5 a), each tooth is bifid and a little hollowed out, so as to receive the points of the two inwardly projecting margins which form each suture. Ridges, more or less prominent, running from each of the six marginal teeth, extend towards the centre of the cup. These six teeth cannot be seen from the outside. The edge of the cup is rarely crenated; but I have seen two instances in which this was the case.

Cirri.--In the first pair, the rami are not quite so unequal as in A. spongites; the longer ramus being about twice as long as the shorter. In the third pair, there are some very minute, thick, upwardly-pointing spines, which I did not notice in A. spongites. In the fourth pair, the spines are a little more crowded, with longer dorsal tufts, than in the sixth pair; and they are mingled with some very minute, thick, upwardly pointing spines. In young individuals, there are only three pairs of main spines on the segments of the sixth pair, instead of four pairs.

6. ACASTA LÆVIGATA. Pl. 9 fig. 6 a, 6 b.

ACASTA LÆVIGATA. J. E. Gray (!). Annals of Philosophy, (new series), vol. 10, Aug. 1825.

Parietes internally quite smooth, with the lateral margins of each compartment inwardly prominent: basis with the edge strongly crenated, and furnished with six inwardly prominent teeth: scutum feebly striated longitudinally, or smooth.

Var. (a), epidermis coloured dull orange.--Red Sea.

Hab.--Red Sea, Philippine Archipelago; Mus. Brit., Cuming, &c.

This species, of which I have examined many specimens from the above two and other unknown localities, agrees in all essential points of structure with A. glans, and consequently I for some time classed them together; but the characters, though usually of small value, by which this form differs from A. glans being apparently constant, I have with some doubt allowed it to remain specifically distinct. These characters are, firstly, the much smaller size of the whole shell in A. lævigata; secondly, the edge of its basal cup being always crenated, which seems to be a rare accident in A. glans; thirdly, though of secondary importance, the scutum being here less plainly striated; and, lastly, the spur of the tergum being of less breadth, and of a more rounded outline; on the other hand, it must be confessed, that when small specimens of A. glans are taken, there is hardly any difference in the spurs of the terga.

General Appearance and Structure of Shell.--The surface of the shell is often very smooth, but is sometimes studded with some small sharp calcareous points. The colour is white, or pale reddish-brown; but in the specimens from the Red Sea, the tint is more orange, with the upper part of the shell white. The orifice of the shell is unusually small. The largest specimen which I have seen was only .25 of an inch in basal diameter, and therefore less than half the size of A. glans. The internal surfaces of the parietes are smooth, with the two lateral margins inflected, as in A. glans. The edge of the basal cup has six knob-like teeth, like those in A. glans, but smaller; and, in addition, it is finely crenated.

Scuta: these differ only in being less plainly striated in longitudinal lines; indeed, some specimens show hardly a trace of this structure. Terga; these valves, in some varieties (Pl. 9, fig. 6 b) can hardly be distinguished from those of equal size from young individuals of A. glans; other varieties have the spur (Pl. 9, fig. 6 a) not truncated, but broadly pointed, and therefore of considerably different shape.

Neither in the mouth, nor cirri could I detect any difference with A. glans.

7. ACASTA FENESTRATA. Pl. 9, fig. 7 a-7 c.

Shell reddish, with six large, membrane-covered apertures between the sutures, above the basal cup: carino-lateral parietes half as broad as lateral parietes; internally, parietes and edge of basis smooth; tergum with the articular ridge short and prominent; spur pointed.

Hab.--Philippine Archipelago, Mus. Cuming.

General Appearance.--Shell rather elongated or tubular; with the upper part reddish, and the surface roughened with very minute points. The basal cup is generally as deep as the shell is high, ending downwards in a blunt point, often curved to one side. The summits of the radii, as usual, are oblique. The parietes of the carino-lateral compartments are about half as wide as the parietes of the lateral compartments, and are therefore of greater proportional width than in the foregoing or any other species of the genus. The large membrane-covered openings, or, as they may be called, windows, presently to be described, between the lower halves of the compartments, is much the most remarkable character of this species. The largest specimen which I have seen was only .23 in diameter, and .6 of an inch in height, measured from the basal point of the cup to the tips of the compartments.

Scuta.--These barely exhibit a trace of longitudinal striæ. The valve is rather thick and convex. The basi-tergal angle is much rounded off. Internally, the articular ridge is thick and rather prominent. Terga: the valve is furrowed in the line of the spur: the spur is pointed and rather long; it is distinctly separated from the basi-scutal angle of the valve, and the basal margin on the two sides of the spur forms a straight line. The articular ridge is prominent, and short.

Structure of the Parietes, Radii, and Basis.--The parietes are internally quite smooth down to its basis. The edges of the radii are also smooth, as is the edge of the basal cup. The alæ project less than usual. The radii are of moderate breadth, they extend downwards only a little below the sheath, namely, about half way down the shell, where they terminate, as usual, in a point. The increase in width, during growth, of the radii, and their not extending down to the basis, would necessarily cause a gap between the opposed edges of the walls, in the portion beneath the radii; but besides this, the edges of the walls themselves, beneath the radii, and on the opposed side beneath the alæ, are hollowed out, but on the latter side or beneath the alæ sometimes in a lesser degree. The result of this is, that the compartments, in their lower halves, are separated from each other by membrane-covered windows or apertures, arched at their upper ends, and of considerable size, namely, about as wide as the parietes of the carino-lateral compartments. I have only further to remark, that during the downward growth of the parietes, the apertures increase in size, but at the same time become closed up at their upper ends; and the arched layers of shell added at these upper ends, assume a very different aspect from the rest of the parietal surface,--appearing like two wedges, with their points upwards, let in, on one side of the suture, between the ordinary parietal surface and the radius, and, on the other side of the suture, between the ordinary parietal surface and the recipient furrow of the radius.

The animal's body was in a bad state of preservation; but, as far as I could make out, the cirri resembled those of A. glans.

Affinities.--This species differs from A. glans in not having the internal margins of the compartments projecting inwards. It differs from all the ordinary varieties of A. spongites, in the smoothness of the basal edges of the parietes and of the edge of the cup; in the greater width of the carino-lateral compartment, though this is a variable point in A. spongites; slightly in the shape of the scuta and terga; and, lastly, in the large, membrane-covered openings between the compartments.

8. ACASTA PURPURATA. Pl. 9, fig. 8 a-8 c.

Shell dull blueish-purple, with six small, membrane-covered apertures between the sutures, close above the basis: tergum with the articular ridge very short and prominent; spur very broad and rounded.

Hab.--Sumatra; Philippine Archipelago; imbedded in the bark of an Isis; Mus. Cuming, Stutchbury, Brit.

This species is perfectly distinct from the others, as shown by its general appearance, its habits, and the structure of its opercular valves: it is allied to A. fenestrata, in having membrane-covered apertures between the compartments, and in some respects in its opercular valves: it is also allied to A. sulcata and cyathus in the parietes being often internally ribbed, in the basal cup having a crenated edge, and in the anterior ramus of the fourth cirrus being furnished with the minute hook-like spines.

General Appearance.--Sub-globular, slightly compressed, with a rather small orifice; smooth, but sometimes furnished with sharp shelly points; dull purple, more or less dark, with the upper parts of the walls often white. The radii are rather narrow, and generally white, with their summits only slightly oblique, but variable in this latter respect. The parietes of the carino-lateral compartments are narrow, being only one sixth of the width of the parietes of the lateral compartments. In some specimens there are membrane-covered apertures of considerable size, in others mere narrow clefts, between the basal halves of the compartments. The basal cup is moderately deep. The largest specimen was only .16 of an inch in basal diameter.

Scuta, rather broad, externally convex, not longitudinally striated: articular ridge prominent, short, not extending down above one third of the length of the valve. Depression for the adductor muscle deep. On the internal surface, near to the rostral angle, a rather large purple spot of corium adhered to the valve. Terga, broad, externally rather convex: scutal margin protuberant: carinal margin slightly inflected, or furnished internally with a rim: articular ridge prominent, very short, not extending down above one fourth of the valve. Spur very broad, rounded, confluent with the basi-scutal angle of the valve.

Internal Structure of the Parietes, Radii, and Basis.--The parietes, internally, are either quite smooth, or more commonly ribbed, with the basal edge in consequence crenated; the ribs are either placed at an unusual distance from each other, and consequently are few in number, or are pretty close together. The edge of the basal cup is either quite smooth, or closely crenated, or distantly toothed, in conformity with the state of the internal surface of the parietes. The radii have nearly smooth edges, with their summits more or less oblique. They sometimes extend down only three fourths, or only two thirds, of the length of the shell, and the margins of the parietes under the radii being a little hollowed out, the sutures are converted into clefts or apertures (of course covered by membrane) like, but not so large as, those in A. fenestrata. The margins of the parietes are hollowed out only on the side of the radius, and not on both sides of the sutures, as is most usual in A. fenestrata. In some specimens the radii extended down close to the basal cup, and only very minute clefts were left between the opposed edges of the parietes.

In the animal's body the only noticeable character was, that on the anterior ramus of the fourth pair of cirri, some of the segments were furnished with very broad and thick, small, downwardly curved, teeth or hooks, like those described in certain varieties of A. sulcata; but they are here stronger and thicker. The segments in the three posterior pairs of cirri are not so much elongated, as in the other species.

9. ACASTA SPORILLUS. Pl. 9, fig. 9 a-9 d.

Shell purplish-brown, with the parietes internally strongly ribbed and reticulated: carino-lateral compartments extremely narrow, not extending down to the basis.

Hab.--Sooloo Islands, East Indian Archipelago; Mus. Dana.

I am indebted to Mr. Dana, the distinguished naturalist of the United States Antarctic Expedition, for two specimens of this interesting species, which, in the singular reticulated structure of the inner surface of the walls, and in the almost rudimentary condition of the carino-lateral compartments, not extending down to the basal cup, is very distinct from the foregoing species. I have used Mr. Dana's very appropriate MS. name of sporillus. The specimens were dredged up, lying quite loose and unattached at the bottom of the Sooloo sea; the one which I opened, must have long lain dead; but Mr. Dana assures me that some were living, and he has sent me drawings of parts of the mouth and cirri: I am much surprised at this circumstance; for analogy would have made me believe that this species must have been imbedded in some sponge-like body, such as the bark of a zoophyte, and that it could not have lived unattached. I may add that a small fragment of a brown leathery substance adhered to the upper end of one of the two specimens, and this seems to indicate attachment.

General Appearance.--Shell shaped like a pointed acorn; slightly flattened; orifice extremely small; surface very finely punctured, covered by a purplish-brown epidermis, with transverse stripes of different shades, and with the apex dark; according to Mr. Dana, when fresh, the colour was purplish-carmine. Radii narrow, white. The carino-lateral compartments are extremely narrow; the wall-portion (fig. 9 b) forming a mere linear rib, terminating downwards in a sharp point, which does not reach the basal cup: hence this compartment evidently tends to become rudimentary. The basal cup is moderately deep and pointed. Basal diameter .16; height, from the bottom of the cup to the top of the shell, .24 of an inch.

Scuta: narrow, with the upper part produced; not striated longitudinally; coloured by a pale purple, longitudinal band. Internally, there is scarcely a trace of an articular ridge, which, in the other species, is always more or less developed. Terga with the spur bluntly pointed; nearly the whole basal margin, on the carinal side, slopes towards the spur.

Internal Structure of the Parietes, Radii, and Basal Cup.--The parietes are strongly ribbed internally; and these ribs are connected by very narrow, less prominent, transverse, slightly branched ridges, giving a reticulated structure to the inner surface. Between several of the main longitudinal ribs, in the lower part of the shell, new ribs may be seen in process of formation, and these tend to convert the reticulated structure into a double row of minute cells. I have not met with an exactly similar structure in any other cirripede; but I have no doubt that the little transverse ridges are homologous with the transverse calcareous septa in the parietal pores of many Balani, in the same manner as the internal longitudinal ribs, in this and other species of Acasta, are homologous with the longitudinal septa forming the above pores. The edge of the basal cup is pectinated with teeth, which lock into the teeth formed by the ends of the internal parietal ribs. The radii are narrow, and have smooth edges. The alæ project beyond the parietes to a remarkably small extent. The sheath is free, or hollow beneath. I have already described the almost rudimentary condition of the carino-lateral compartments; this is best exhibited in an internal view of the two compartments, as given in Pl. 9, fig. 9 b.

Animal's body unknown to me: from Mr. Dana's drawing the three posterior pairs of cirri seem to have been much elongated: and the rami of the first pair, as usual, unequal in length.

M. Deshayes has given an indifferent figure and imperfect description of ACASTA TUBULOSA (Guerin, Magasin de Zoologie, 1831, Tab. 39; and Guerin, Iconographie du Règne Animal, Mollusques, Tab. 38, fig. 4, but here by a misprint called A. spinulosa); it is utterly impossible to recognise the species of this genus from such materials.

3. Genus--TETRACLITA. Pl. 10, 11.

TETRACLITA. Schumacher. Essai d'un Nouveau Syst., &c., 1817.

CONIA. Leach. Journal de Physique, tom. 85, 1817.[105]

ASEMUS. Ranzani. Memoire di Storia Naturale, 1820.[106]

POLYTREMA. De Ferussac. Dict. Classique d'Histoire Naturelle, 1822.

LEPAS. Gmelin. Systema Naturæ, 1789.

BALANUS. Bruguière. Encyclop. Method., 1789.

---- Lamarck. Animaux sans Vertèbres, 1818.

[105] From a note by the Editor, it appears that Schumacher's essay appeared before the number of the Journal containing Leach's paper, so that Schumacher's name must be adopted.

[106] I have not seen a complete copy of this work, and give the title from a catalogue; the running heading of the part containing the Cirripedia, is "Opuscoli Scientifici."

Compartments four, sometimes externally calcified together: parietes permeated by pores, generally forming several rows. Basis flat, irregular, calcareous, or membranous.

Hab.--Throughout the tropical and warmer temperate seas.

General Appearance.--The shell is conical, more or less depressed, and very rarely, even when growing in crowded groups, becomes cylindrical or elongated. The orifice is seldom large, generally diamond-shaped or oval. The colour is either nearly white or purple, occasionally even inky black, or very dark green, and sometimes of a pale pink peach-blossom. The surface is sometimes smooth, but more commonly longitudinally ribbed; the outer lamina of shell is very often wholly corroded away, excepting close to the basis, leaving the solidly upfilled parietal tubes exposed: these give the shell a striated appearance, or they appear like flattened tapering points adpressed to its surface (Pl. 10, fig. 1 b): Lamarck attempted to express this appearance, by using the specific name of stalactiferus. The colour of the shell depends, to a considerable extent, on the colour of the shelly matter in these exposed parietal tubes. We shall presently see that the corrosion and disintegration, to which some of the species are so liable, plays an important part during their growth. The radii are either well developed, as in most of the species; or they are entirely absent, as in the great majority of specimens of T. porosa and serrata. In many individuals of T. porosa and purpurascens not only are the radii absent, but the four compartments are calcified together without any trace, on the external surface, of the sutures. The largest specimen which I have seen of T. porosa, which is the largest species, was two inches in basal diameter, and nearly one inch and a half in height.

Scuta.--These valves are sub-triangular, and either longitudinally or transversely elongated. Externally, the growth-ridges are moderately prominent, and in T. costata and cœrulescens they are crossed by longitudinal striæ. Along the occludent margin, the inflected extremity of each alternate growth-ridge is generally much thickened,--a set of teeth being thus formed, by which the two valves are locked together. In T. porosa, this character is variable, for sometimes every alternate ridge, and sometimes only two or three ridges, separated from each other by several growth-ridges, are thus developed into teeth. The articular ridge is either moderately prominent, or is extremely prominent, as in T. cœrulescens; but the lower edge in no case depends as a free, hinge-like style, as sometimes in Balanus. The adductor ridge is generally well developed and distinct from the articular ridge: in T. purpurascens it is very blunt: in T. serrata it is united to the articular ridge half way up it, thus forming a deep tubular cavity running up to the apex of the valve: in T. cœrulescens, the adductor ridge is very short, and is united to, or almost continuous with, the lower end of the articular ridge, a small sub-cylindrical tubular cavity being thus formed. Small crests exist for the attachment of the rostral and lateral depressor muscles, in most of the species, excepting T. purpurascens and costata, in which, however, more especially in the former, there are, instead of crests, minute pits for the attachment. These crests vary much in prominence in the same species.

Terga.--These valves present no essential differences from those of Balanus; they are sometimes beaked, and the beak is hollow and occupied by a thread of corium, as in that genus. The external surface of the valve is often depressed in the line of the spur, but there is never a longitudinal furrow with the edges folded in, as in Balanus. The spur is very short in T. purpurascens. In T. radiata, the articular ridge is remarkably prominent. The crests for the depressor muscles are well developed in all the species. The shape of the terga is variable in nearly all the species, and greatly so in T. porosa.

Compartments.--Owing to there being only four compartments, the lateral pair are large; the size of the carina relatively to the rostrum varies, according as its alæ have been added to during diametric growth. The walls are very thick, and are composed of numerous tubes, in some species as many as fourteen or fifteen rows being exposed on the basal margin (Pl. 10, fig. 1 g). The tubes are generally angular, and slightly elongated in the ray of the circular shell; sometimes they are nearly circular and small. New tubes are formed only at the basal edge of the outer lamina, by the bifurcation of the septa which form the tubes. In very young specimens there is only a single row of tubes; and in T. rosea this holds good throughout life: in this species (fig. 3 d) the tubes, in the single row, are large and quadrangular, and the outer lamina of shell is strengthened by numerous, small, internal, longitudinal plates. I believe the branching septa, which separate and form the parietal tubes, correspond with the longitudinal septa in the more simple walls of Balanus. The tubes become solidly filled up, in their upper parts, with hard, and generally coloured shelly matter. The degree to which they are filled up differs in the different species; the external side of each tube is always first thus coated. The thin outer lamina of shell, in several of the species, commonly disintegrates and disappears; the upfilled parietal tubes being thus exposed. The inner lamina of the walls is generally smooth, but in T. radiata it is longitudinally ribbed, as in most species of Balanus. The sheath is generally dark-coloured; its lower edge does not project or overhang the inner lamina, as is usual in Balanus, excepting in T. serrata, and in some few varieties of T. porosa.

The Radii, when developed, are either narrow or broad, with their summits either oblique or extending in a straight line from the top of one compartment to that of another. In T. serrata, I have not seen a single specimen with the radii developed; in T. porosa, they are very seldom developed, and then, apparently, only in quite young specimens, in which they are narrow; in T. purpurascens, they seem to be about as often developed as not, and when present they are broad; in T. costata, cœrulescens, and radiata, they are always largely developed. In some specimens of the species, in which the radii are not developed, even the sutures do not reach the external surface; the outer lamina of the parietes being continuous all round, so that the shell seems formed of a single piece. Even in such specimens, the four compartments, viewed from within, can be seen to be distinct; and the sutures can generally be traced across the whole thickness of the parietal tubes; in this latter case, when the sutures are broken open, the radii are seen to be represented (Pl. 10, 1 h) by a few small sinuous ridges. Owing to the disintegration of the upper and outer part of the shell, and the consequent exposure of parts of the sheath and alæ, the radii sometimes appear as if developed, when such is not the case. With respect to the internal structure of the radii, they are formed, in T. purpurascens and costata, of tubes, like those of the parietes, and therefore according to the normal plan; whilst in the other species they are formed by longitudinal sinuous ridges, sending out on each side irregular denticuli; and the interspaces between the ridges are filled up solidly during the growth of the radii, in all the species, except in T. radiata, in which they are left to a considerable extent open. These sinuous ridges, with their denticuli, homologically represent the branching septa which form the parietal tubes. The edges of the alæ are crenated in all the species, except in T. costata.

Diametric growth.--When first examining groups of T. porosa, in none of which the radii had been developed, and in which, consequently, the shell could not have grown in diameter, but only at its basal margin, I was at first unable to comprehend, how the upper part of the shell and the orifice could have acquired their proper proportional width. The young shell, at its first formation, starts with an orifice so small that a pin could hardly be inserted in it; and this in many individuals is never increased in diameter by the diametric growth of the shell; but in place of this, as the conical shell is added to at its base, the whole upper part disintegrates and wears away, the orifice becoming thus enlarged. We thus see that the corrosion and wearing away of the upper part of the shell is a necessary element in its growth. The development of the radii, which in some of the species, as in T. purpurascens, at first seems to be quite capricious, really depends upon the fact, whether the specimens have been exposed to disintegration; for I have almost always found that when the outer lamina of shell has been well preserved, the radii have been developed, and the orifice has been enlarged by their growth, instead of by the wearing down of the upper part of the conical shell.

Basis.--This consists of a very thin, flat, though irregular, translucent, calcareous plate, which towards the edges is sometimes membranous. In T. purpurascens, the basis is entirely membranous. When a portion of the calcareous base is dissolved in acid, a tissue is left, composed of several laminæ, to which numerous bifurcating cement-ducts are attached: even before dissolution, these delicate bifurcating ducts can just be perceived by the aid of a simple lens.

Mouth.--The several organs present no particular characters. There are generally three teeth on each side of the notch in the labrum. The palpi usually have parallel sides, but are club-shaped in T. purpurascens and costata. The mandibles have generally four teeth, but there are five in T. vitiata, and only three in T. costata. The maxillæ are notched. The outer maxillæ are bilobed in front.

Cirri.--The segments of the three posterior pairs usually support only three pairs of main spines, but there are four pairs in T. vitiata and costata: between each pair, there is either a tuft of fine spines, or a single fine spine. The rami of the first cirrus are unequal in length. In the third cirrus, the posterior ramus is sometimes much elongated, but sometimes both rami are short and blunt. Some of the segments in the third cirrus often support very coarsely and doubly pectinated spines. Under the head of T. porosa, it will be seen to what a remarkable degree the relative numbers of the segments in the several cirri vary, even in specimens taken out of the same cluster.

The Branchiæ are well developed (at least in T. porosa and costata), as a large, plicated, tapering fold, with a small second fold on the inner side at the base. In T. porosa the stomach is destitute of cæca. The vesiculæ seminales in this same species are large, with their broad, blunt ends reflexed. The ovarian tubes surround the sack, and cover the basal plate.

Distribution and Habitats.--This genus is confined to the tropics, and to the warmer parts of the temperate seas: in the southern hemisphere, it ranges south, to the Cape of Good Hope and to Van Diemen's Land: in the northern hemisphere it does not appear to range so far; I do not know of any authentic case of a species having been found in the Mediterranean, or on the shores of the United States, north of the West Indies. Tetraclita porosa is found round the whole world; T. radiata, also, has a very wide range, inhabiting the West Indies, the East Indian Archipelago, and New South Wales. This latter species, as well as T. cœrulescens, is often attached to the bottoms of ships, adhering to Balanus tintinnabulum. The several species live attached to tidal rocks, to littoral shells, or to massive corals. I have met with two instances, in the West Indies and the Philippine Archipelago, of T. porosa adhering to wood. Tetraclita porosa seems to feed chiefly on crustaceans: the number and the size of the amphipods, isopods, and entomostracans, together with an annelid, in the stomachs of some specimens from South America, was quite surprising. As many as five species occur in the same region, in the eastern half of the world; thus on the shores of New South Wales, we have T. porosa, vitiata, radiata, purpurascens, and rosea; in the Philippine Archipelago, we have T. porosa, vitiata, costata, and cœrulescens.

I have not seen any species of this genus fossil.

Variation.--The species vary in shape nearly, but not quite as much as in Balanus, for we very rarely here see cylindrical varieties; but in the same species, we have extremely depressed, steeply conical, and convex forms; the orifice varies in relative size; the state of the surface, whether ribbed or smooth, whether well preserved or corroded, the upfilled parietal tubes being thus exposed, varies more than in Balanus. The colour also varies; specimens of T. porosa (Pl. 10, fig. 1 a to 1 f) being dark purple, or even inky black, white, pale pinkish-purple, and green: as far as I have seen, the pinkish varieties of T. porosa are confined to the eastern half of the world. Even the ridges and crests on the under side of the scutum vary in some degree; and the tergum in T. porosa varies considerably, and in some of the other species, slightly, in general shape: I believe that the tergum becomes narrow and elongated, when the shell is steeply conical, with the orifice of small diameter. After having spent several days in disarticulating and closely examining the many specimens of T. porosa in my possession, I concluded that its varieties formed at least four species, these being in external appearance extremely distinct; but ultimately the many intermediate forms compelled me to unite all into a single species. Again, I may instance the conical, ribbed variety of T. purpurascens (Pl. 11, fig. 1 b), with the outer lamina of the shell preserved and with the radii widely developed, as having not the smallest resemblance to the other common depressed variety (fig. 1 a), having a granulated surface, produced by the exposed tips of the upfilled parietal tubes, and without a trace of the radii or even of the sutures; I may add that, according to the characters used by some authors, these two varieties would be classed in two separate genera.

To distinguish the species of this genus, the chief reliance must be placed (as in the case of most other sessile cirripedes) on the general outline of the opercular valves, and on the ridges and crests on their under sides: the internal structure, however, of the radii, and in a lesser degree of the parietes, must not be overlooked. I have not found the parts of the mouth, or the differences in the cirri, of much service; and it will be shown under T. porosa, that the relative numbers of the segments in the several cirri, and even their shape, is extraordinarily variable.

Affinities.--All the species are pretty closely allied, and there is no ground for making any sectional division of the eight species, more especially not on the ground whether or no the radii are developed. Tetraclita purpurascens, taking into account all the characters, including the animal's body, is perhaps the most distinct species in the genus, but it is closely allied to T. costata. In the well-marked character of the parietes being formed of a single row of large tubes, T. rosea differs from all the other species. The genus is closely allied to Balanus; I can point out no difference in the animal's body, nor any constant difference in the opercular valves. The ridges and crests on the under sides of the scuta are more prominent in Tetraclita; and all the species, excepting two, have crests (though sometimes very slight) for the attachment of the rostral depressor muscle, and these occur only in two species of Balanus: crests, also, for the attachment of the lateral depressor muscle are common in Tetraclita, but rare in Balanus. The main character, however, of the genus, as compared with Balanus, is derived from the existence of only four compartments, and in a lesser degree from the several rows of parietal pores; but, as just stated, T. rosea has only a single row, and, on the other hand, in Balanus crenatus, there is a slight tendency exhibited, in the dividing of the longitudinal septa near the outer lamina, to form a second row of parietal pores; and in B. cariosus, moreover, we actually have two or three rows of irregular and very short pores. The thin, yet solid calcareous basis which occurs in all the species of Tetraclita, excepting T. purpurascens, resembles the basis in Balanus flosculus and imperator, but I suspect that the structure of the cement-ducts is different in the two genera.

1. TETRACLITA POROSA. Pl. 10, fig. 1 a-1 m.

LEPAS POROSA. Gmelin. Syst. Naturæ, 1789.[107]

BALANUS SQUAMOSUS. Bruguière. Encyclop. Method., 1789, Pl. 165, fig. 9, 10.

LEPAS FUNGITES. Spengler. Skrivter af Naturhist. Selskabet, 1 B., 1790.

---- POROSA. Wood's General Conchology, Pl. 9, fig. 4, 1815.

TETRACLITA SQUAMULOSA. Schumacher. Essai d'un Nouveau Syst., &c., 1817.

BALANUS STALACTIFERUS. Lamarck. Animaux sans Vertèbres, 1818.

---- ---- Chenu. Illust. Conch., Pl. 4, fig. 6, 7.

ASEMUS POROSUS. Ranzani. Memoire di Storia Naturale, Tab. 3, fig. 32-35.

CONIA POROSA. Sowerby. Genera of Recent and Fossil Shells, Plate, 1823.

---- ---- Leach. (sine descript.) Encyclop. Brit. Supplement, vol. 3, 1824, Tab. 57.

[107] As Gmelin and Bruguière published the same year, I do not know which comes first, but I have adopted the best known name. Most authors give, amongst their references, Chemnitz, vol. 8, Tab. 98, fig. 836, 837, but the accompanying description is more applicable to T. serrata of this work than to T. porosa; without a figure or description, however, of the under side of the scutum it is impossible to decide. Several authors, also, give Lepas cariosa of Pallas, as a synonym; this, however, is the Balanus cariosus of this work.

Radii rarely present, when present narrow; even the sutures often absent: shell steeply conical, with the surface generally corroded, and having a stalactiferous appearance.

Var. (1) communis (Pl. 10, fig. 1 a): outer lamina of shell almost wholly removed; the portion preserved, as well as the exposed parietal tubes, gray, or pale dirty brown, or dull purple.

Var. (2) nigrescens (Pl. 10, fig. 1 c): outer lamina of shell almost wholly removed; the portion preserved, and the exposed parietal tubes, very dark purple or inky black.

Var. (3) viridis: outer lamina of shell almost wholly removed; the portion preserved, and the exposed parietal tubes, green; under surface of opercular valves clouded green.

Var. (4) rubescens (Pl. 10, fig. 1 b): outer lamina of shell almost wholly removed; the portion preserved, and the exposed parietal tubes, pale reddish-purple, or peach-blossom purple; under surfaces of opercular valves often reddish purple; terga often rather narrow, with the spur somewhat pointed, and with the basal margin on the carinal side sloping, or not making an angle with the spur.

Var. (5) elegans (Pl. 10, fig. 1 d): outer lamina preserved, excepting sometimes near the summit of the shell; white, tinged with yellowish brown from the epidermis; surface strongly ribbed longitudinally; orifice rather small; sheath reddish-purple; terga narrow, with the basal margin sloping as in var. rubescens.

Var. (6) communis (young) (Pl. 10, fig. 1 e): radii developed, very narrow; outer lamina of shell preserved, gray or dull purple; surface slightly ribbed longitudinally.

Var. (7) patellaris (Pl. 10, fig. 1 f): radii developed, very narrow, white; outer lamina of shell preserved, generally reddish-purple; steeply conical, with the orifice extremely small; surface smooth, with longitudinal white ribs. Terga very narrow, with the spur sharply pointed, and with the basal margin on the carinal side sloping towards it, or not making an angle with it. Scuta, with the adductor ridge very prominent. Attached to a ship's bottom.

Hab.--West Indies, Brazil, West Colombia, Panama, Galapagos Archipelago, California, Philippine Archipelago, China, East coast of Australia, Red Sea; generally attached to tidal rocks, sometimes to shells, sometimes to wooden posts. Very common.

General Appearance.--This, the widest-distributed and much the commonest species of the genus, varies greatly in external appearance. The usual shape is steeply conical, but some individuals are much depressed. In the common varieties the outer lamina of shell has been removed even close to the basal edge; the upfilled parietal tubes being thus exposed (fig. 1 b), as flattened adpressed points. These points are largest in large specimens, but they vary somewhat in size in specimens of equal growth. When the outer surface is preserved, it is generally ribbed longitudinally, but is sometimes quite smooth. The most general colour is dirty gray or dark purple; but many specimens are pale pinkish-purple, owing to the exposure of the parietal tubes upfilled with shelly matter of this tint: there are also, as given under the characters of the vars., black, white and green varieties. The sheath is always tinted by the prevailing colour. The radii are rarely developed, but generally the four sutures are distinct; sometimes these are externally quite obliterated, the shell, as seen from the outside, consisting of a single piece like a patella or fissurella. When the radii are developed they are very narrow, with their upper edges oblique: their development seems always coincident with the more or less perfect preservation of the shell, and their function is to enlarge the orifice; the enlargement being usually effected by the disintegration and removal of the whole upper part of the conical shell. The size of the orifice varies considerably; in the seventh variety it was extraordinarily small: in outline it varies from oval to rounded trigonal or rhomboidal; in some specimens, with the radii well developed, it was rounded pentagonal.

Size.--Tetraclita porosa is the largest species of the genus; I have seen specimens attached to a large pebble of granite in the British Museum, which measured two inches in basal diameter, and nearly one inch and a half in height.

Scuta: these are sub-triangular and generally a little elongated, but they vary slightly in relative breadth (fig. 1 i, 1 l), and likewise in the degree to which the basi-tergal angle is rounded off. The under surface is clouded with dull or pinkish-purple, or with green, or is nearly white. The articular ridge is not prominent, and the articular furrow is narrow. The adductor ridge is prominent, and runs upwards for some distance close and parallel to the articular ridge; and sometimes it extends nearly or quite up to the apex of the valve; in one single specimen the adductor ridge had an abraded appearance, and was very little developed. The crests for the rostral and lateral depressores are sharp and distinct. Along the occludent margin, the ends generally of the alternate lines of growth are enlarged into knobs, serving to lock the two valves together; but in many specimens only two or three knobs, at intervals of several lines of growth (fig. 1 b), are developed.

Terga: when the upper end of the valve is not corroded, there is a distinct beak, hollow within for a thread of corium. The scutal margin is not much inflected, and the articular ridge not very prominent. The spur is placed quite close to the basi-scutal angle of the valve, so that there is no basal margin on that side of the valve. The width of the valve and of the spur, and the acumination of the extremity of the latter, varies in a remarkable manner. In the broad and commonest variety (fig. 1 k), the basal margin of the valve form an angle of about 130° with the carinal side of the spur, and the basal end of the spur is broad and truncated. In the less common and narrow variety (1 m), the basal margin in some extreme cases forms very nearly a straight line with the carinal side of the spur; and the spur itself is bluntly pointed: in var. 7 it is sharply pointed.

Structure of the parietes and radii.--In all cases the four sutures are quite distinct, from top to bottom, on the internal lamina of the shell, and generally they run through the whole thickness of the walls, and are visible externally. Often they do not quite reach the outer lamina, and then the shell externally consists of a single piece, like a patella. Sometimes the sutures can be traced running through the parietal tubes only for a short distance from the internal surface; where they cease, the two walls of the suture become fused together. When a perfect suture is split open, the radius is represented (fig. 1 h) by a few narrow, sinuous ridges, sending out on each side little branches or denticuli; these are received into corresponding furrows in the opposed compartment. These ridges run nearly parallel to each other, and somewhat obliquely, from the outer lamina of the shell to the basis. When the radii are developed, their edges are similarly formed, by sinuous denticulated ridges, with the interspaces between them filled up solidly. The alæ are but little prominent.

The mouth does not deviate from the generic type. The cirri are remarkable from the variability in the several pairs of the relative numbers of their segments, as shown in the following table. The segments do not correspond even on opposite sides of the same individual, as may be seen in the two lower lines of the table. I believe that variability to this degree is very uncommon in other cirripedes, though, as stated in the Introduction, the number of the segments always increases with the growth of the individual. The terminal segments in the longer rami of both the first and third cirrus are antenniformed,--being elongated, and of a different shape, with fewer bristles, compared with the basal segments of the same cirri. It is apparently these terminal segments which are particularly liable to vary in number. In both rami of the third cirrus, some of the segments, from the sixth to the eleventh inclusive, (counting from the bottom), more especially the eighth, ninth, and tenth, carry a few spines coarsely and doubly pectinated; but as some of the adjoining segments carry spines which may be called doubly serrated, it is not easy to draw an exact line of demarcation. Sometimes, though rarely, a few of the nearly terminal segments in the second cirrus are furnished with similar, doubly pectinated spines.

Numbers of the segments in the rami of the Cirri, in different specimens.

+------------------+--------------+--------------+--------------+-------+ | |First cirrus. |Second cirrus.|Third cirrus. |Sixth | | | | | |cirrus.| | |--------------+--------------+--------------+-------| | |Shorter|Longer|Shorter|Longer|Shorter|Longer|Either | | |ramus. |ramus.|ramus. |ramus.|ramus. |ramus.|ramus. | |------------------+-------+------+-------+------+-------+------+-------| |Specimen from | | | | | | | | |Pernambuco, Brazil| 9 | 19 | 10 | 11 | 15 | 27 | 26 | |(var. 1) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |Another specimen | | | | | | | | |from the same | 12 | 23 | 12 | 14 | 14 | 19 | 23 | |cluster | | | | | | | | |(var. 1) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From the Galapagos| | | | | | | | |Archipelago, | 10 | 16 | 10 | 11? | 11 | 16 | 25 | |(var. 1) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From the | | | | | | | | |Philippine | 10 | ? | 10 | 10 | 11 | 19 | 18 | |Archipelago, | | | | | | | | |(var. 4) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From California | 15 | 24 | - | - | - | - | 22 | |(var. 5) | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From the bottom | | | | | | | | |of a ship | - | - | 9 | 9 | 10 | 17 | 14 | |(var. 7), | | | | | | | | |young | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |From South America| | | | | | | | |(var. 1) | 11 | 18 | 11 | 12 | 13 | 21 | 22 | |British Museum | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |Another specimen | | | | | | | | |from the | 16 | 25 | 13 | 18 | 15 | 23 | 27 | |same cluster with | | | | | | | | |the last specimen | | | | | | | | |------------------+-------+------+-------+------+-------+------+-------| |Same individual, | | | | | | | | |but the cirri | 15 | 28 | 15 | 21 | 16 | 23 | - | |from the opposite | | | | | | | | |side of the body | | | | | | | | +------------------+-------+------+-------+------+-------+------+-------+

Varieties.--Under the generic description, I have stated that after having spent some time in examining a very large suite of specimens of T. porosa, I concluded that at least four of the varieties were true species. It so happened that all the specimens which I first examined of the var. (4) rubescens, had the narrow sloping terga, and scuta with only two or three great teeth on their occludent margins; but ultimately, in a group thus characterised, I found one or two individuals with terga precisely of the shape of those in var. (1) communis. Again, in a group of dull purple specimens of var. communis, a few had the narrow sloping terga, and scuta with teeth on their occludent margins, intermediate in size and number between the varieties with only one or two great teeth, and those with every alternate growth-ridge enlarged into a tooth. Hence var. rubescens completely broke down as a species.

With respect to var. (5) elegans (a M.S. specific name of Leach) I inferred at first, from external appearance alone, that it was distinct; the outer lamina of the shell and even the epidermis is preserved; the surface is strongly ribbed, and the whole shell, excepting the sheath, is nearly white; the terga are narrow, with a sloping basal margin as in var. (4) rubescens. Whole groups of specimens are thus characterised. But as var. communis is often white, and as the surface, when the outer lamina is preserved, is generally, as we shall presently see, ribbed longitudinally, the differences in var. elegans are quite unimportant.

The (6th) var. differs from var. communis only in the narrow radii having been developed, and consequently in the orifice being pentagonal, and in the outer, longitudinally ribbed lamina of the shell having been preserved. In the same group of specimens, I have seen every intermediate stage between this and the common form. It must not, however, be supposed that the young of var. communis always pass through these stages, for such is not the case. In the genus Balanus it has been seen, how capricious in some species is the development of the radii.

Of the other varieties, enumerated at the beginning, no further mention is required, excepting with respect to var. (7), the most singular of all. I have seen only three specimens, sent to me by Dr. Aug. Gould, of Boston, United States, and these from the appearance of their bases I have no doubt had been attached to a ship,--the only instance which I have met with, in the present species. The shell is steeply conical, with the orifice so small as to be reduced to a mere pore; the radii are extremely narrow and white; the shell is thin, with the surface smooth, but ribbed longitudinally and regularly; the outer lamina of the shell and the epidermis are perfectly preserved; the upper part of the shell is reddish purple, which dies away towards the base: careful examination of the apex shows that at the first growth the young shell was blueish-green. The terga are narrow, with a sloping basal margin, as in var. rubescens, but with the point of the spur sharper. I have formerly remarked that the shape of the terga seems influenced by the size of the orifice. The lower edge of the sheath depends freely: I have seen no other instance of this latter structure, so common, but so variable, in Balanus, in the present species, except to a partial extent in one distorted specimen, in Mr. Stutchbury's collection, adhering to Balanus tintinnabulum, and probably taken from a ship's bottom. I may add that this distorted specimen was remarkable from its radii being wider than in any other instance,--from its smooth uncoloured surface without longitudinal ribs,--and from the perfect preservation of the epidermis over its entire surface. Although Dr. Gould's specimens, in external aspect, are absolutely and entirely different from the common varieties of T. porosa, there are so many intermediate forms, and the differences are so little important that I feel no hesitation in attributing them to variation, consequent on the individuals having been exposed to unusual conditions, attached to the bottom of a ship.

2. TETRACLITA SERRATA. Pl. 10, fig. 2 a-2 d.

Shell dark greenish-gray, with narrow, longitudinal, serrated ribs: radii absent: scutum with the adductor and articular ridges forming a cavity, which runs up to the apex of the valve.

Hab.--Cape of Good Hope; Algoa Bay; attached to sandstone and to Patellæ; Mus. Brit., Cuming, and Stutchbury.[108]

[108] I have seen three separate lots of this species all from the Cape of Good Hope; one lot was collected by Dr. Krauss, at Algoa Bay, and I strongly suspect is the species described by him in his 'Südafrikanischen Mollusken' as Conia porosa. If the species, figured by Chemnitz, and mentioned in a note (p. 329), under T. porosa, be the present species, the specimens probably did not come from Tranquebar, on which point Chemnitz speaks only from memory. I have seen one specimen ticketed New South Wales, it is possible, considering the case of T. rosea, that this may be correct, but I should like to have further confirmation before giving it as a habitat.

General Appearance.--Colour dark greenish gray; form steeply conical; surface covered, especially in the lower half of the shell, by numerous, narrow, sharp, longitudinal ridges, but slightly prominent, and serrated or transversely divided into small teeth: when the shell has been much disintegrated, the upper part of the surface consists of the exposed, smooth, rather large, upfilled parietal tubes. I have seen no instance of the development of the radii; sometimes even the sutures are with great difficulty distinguishable, though I believe they always reach the outer surface; sometimes the sutures are wide from the disintegration of the edges of the compartments. Orifice rounded or oval.

Scuta.--The scuta and carinal half of the terga are blueish-green. In the scuta neither the articular ridge or furrow are much developed: the adductor ridge is prominent, and is united to the articular ridge, about half way up the latter, thus forming a rather large, triangular cavity, which runs up to the apex of the valve.

The Terga are beaked. The spur, measured across the upper part, is half as wide as the valve; it is bluntly pointed; it is placed quite close to the basi-scutal angle of the valve, so that there is no basal margin on that side; it curves towards the scutum, its extremity extending beyond the basi-scutal angle.

Structure of the Shell and Radii.--The parietal tubes are rather large, especially those adjoining the inner lamina of the walls. The shell is of singularly little specific gravity, which is due to the parietal tubes not being filled up with shelly matter nearly to so great an extent as in the other species; even in the uppermost part the tubes are not solidly filled up, only their external sides are thickly coated with greenish-black shell, which by corrosion becomes grayish. The radii, as stated, are not developed: the shell breaks with singular facility along the sutures, and the radii are then seen to be most feebly represented by a few very small branching ridges. The alæ have their edges plainly crenated. The sheath is dark green, with the lower edge free.

The Mouth presents no particular characters. With regard to the Cirri, I am doubtful whether any confidence can be placed in the numbers of the segments being constant; but I may state that the second cirrus contained thirteen and sixteen segments in its two rami; the third cirrus only fourteen in both rami; and the sixth cirrus twenty-six segments in both rami. Whereas in every specimen of T. porosa, the longer ramus of the third cirrus contained more segments than either ramus of the second. About half the segments, namely, those in the middle of both rami of the third cirrus, are furnished with coarsely and doubly pectinated spines, like those in T. porosa.

Affinities.--Upon the whole, this species is more nearly allied to T. porosa than to any other. In the cavity formed by the union of the adductor and articular ridges, it is allied to T. cœrulescens. This species differs from all, in its little specific gravity, consequent on the parietal tubes being only slightly filled up, and in the peculiarly serrated, narrow, approximate ridges on the external surface of the walls. The character derived from the adductor ridge, just alluded to, is remarkable. In the shape of the terga, in the absence of radii, and in the structure of the body, this species approaches closely to T. porosa.

3. TETRACLITA ROSEA. Pl. 10, fig. 3 a-3 d.

CONIA ROSEA.[109] Krauss (!). Die Südafrikanischen Mollusken, Tab. 6, fig. 28, 1848.

BALANUS CUMINGII. Chenu. Illust. Conch., Tab. 4, fig. 5.

[109] I am greatly indebted to Professor Krauss for having sent me, for examination, the unique specimen collected by himself in Algoa Bay. There can be no doubt of the identity of the African and Australian specimens. It is a singular circumstance that the same species should occur in these two distant places, and, as far as at present known, not in the intermediate, more tropical coasts.

Shell dirty white, tinged with pink; parietes formed by a single row of large tubes: radii generally narrow: tergum with the spur rather short and broad.

Hab.--New South Wales, Moreton Bay in lat. 27°, Port Jackson, and Twofold Bay; South Africa, Algoa Bay. Attached, in Australia, to littoral rocks and shells; often associated with T. purpurascens, Chthamalus antennatus, and Catophragmus polymerus; Mus. Brit., Cuming, Krauss, Darwin, Stutchbury.

General Appearance.--Shell steeply conical, often rather convex; dirty or brownish white, feebly tinted with pink; external surface generally much disintegrated, and having in the upper part a pillared appearance, owing to the exposure of the upfilled, large, square, parietal tubes, and, in the lower part, a striated (and sometimes serrated) appearance, from the exposure of the parallel, approximate plates, with which the outer lamina of the shell is internally strengthened. In only a few young specimens, the whole outer lamina of the shell was well preserved; and in these the surface was very smooth, and even glossy, giving to the specimens a quite different aspect; even in partially corroded specimens, the lower part of the shell sometimes is quite smooth. Generally, the radii are developed; in most specimens they are narrow, but sometimes of moderate width; their summits are oblique, and their edges often notched or toothed. The recipient furrow, in each opposed compartment, is often almost as wide as the radius itself, and is equally notched. In some much corroded specimens there were no radii. Basal diameter of largest specimen, 1.1 of an inch.

Scuta, generally thick, sometimes very thick, with the external surface usually much corroded: articular furrow rather wide; articular ridge not very prominent; adductor ridge prominent. The rostral depressor muscle is attached in a small oblong pit, sometimes including little crests; and the lateral depressor muscle is attached to what may be described either as three or four parallel furrows or crests.

Terga, with the spur placed close to the basi-scutal angle, so that there is no basal margin on that side; spur short, with its lower end truncated and rounded; broad, even exceeding, when measured across the upper part, half the width of the valve. Articular furrow wide. Apex not beaked.

Structure of Walls and Radii.--This species differs from all the others of the genus in having only a single row (fig. 3 d) of parietal tubes; these are large, quadrangular, but elongated in the ray of the circle. They are not filled up, even at the very top of the shell, but they become thickly lined all round with compact shelly matter. When the surface of the shell is disintegrated, these upfilled tubes greatly affect, as already stated, the external appearance. The outer lamina near the basis is internally strengthened by longitudinal, sharp, approximate ridges or plates, which, also, often affect, after corrosion, the external appearance. The radii have their sutural edges formed by a set of narrow, branching ridges or septa; the ends of which, seen externally, often give a notched outline to this edge; the recipient furrows in the opposed compartments are deep, and their edges likewise are often notched: the interspaces between the branching ridges are filled up solidly. The alæ have their edges coarsely crenated. The lower edge of the sheath is not free.

The mouth and cirri present no particular characters: the third cirrus has both its rami elongated, with the terminal segment tapering. In the three posterior pairs of cirri, the tufts of little spines between the main pairs are rather large.

Affinities.--This species has no particular affinity with any other. The circumstance of there being only a single row of parietal tubes is not so important a difference as might at first be thought, inasmuch as in the other species, during their quite early youth, the walls are formed of only a single row of tubes or pores.

4. TETRACLITA PURPURASCENS. Pl. 11, fig. 1 a-1 d.

LEPAS PURPURASCENS.[110] Wood's General Conchology, p. 55, Pl. 9, fig. 42, 1815.

BALANUS PLICATUS. Lamarck. Animaux sans Vertèbres, 1818.

---- ---- ET PUNCTURATUS. Chenu. Illust. Conch., Tab. 4, fig. 3 et 12.

CONIA DEPRESSA (!). J. E. Gray. Appendix, Dieffenbach's Travels in New Zealand, 1843 (sine descript. vel figurâ).

[110] The descriptions given by Wood and Lamarck are fuller and more accurate than is usual in the case of Cirripedes, and I have no doubt regarding these two names. The Conia depressa of Dr. J. E. Gray is, as I know from having seen the original specimens, the young of this same species; the name is unaccompanied by any description or figure.

Shell depressed, pale purple or dirty white, with the surface longitudinally ribbed, or corroded and granulated: radii or even sutures none, or radii well developed and broad, with their summits parallel to the basis: basis membranous: scutum transversely elongated: tergum small, with the spur extremely short and rounded.

Hab.--Sydney, New South Wales; Flinder's Lagoon, Sir C. Hardy's Island, Barrier Reef; King George's Sound, Western Australia; Van Diemen's Land; New Zealand, adhering to Pollicipes spinosus; Mus. Brit., Cuming, Stutchbury, Darwin, &c. China (?) attached to Pollicipes mitella, Mus. Brit. and Stutchbury. Generally attached to tidal rocks, sometimes to shells. Very common.

General Appearance.--Shell generally much depressed, in a few cases rather steeply conical, in one single instance cylindrical, but not much elongated. Colour, when alive, pale, but fine purple; I presume, judging from some dried specimens, sometimes dirty white. The state of the surface varies remarkably: about half the specimens (fig. 1 a) which I have seen, had the outer lamina of shell quite removed, and the surface granulated, owing to the projecting and exposed tips of the upfilled parietal tubes; the radii are not developed, and often even there is no trace of the four sutures; the rather large orifice is somewhat rounded, and the two scuta, with their surfaces disintegrated, have their middle parts deeply indenting the terga. The shell, in the other and perhaps more common condition (fig. 1 b), has the outer lamina preserved, and is longitudinally ribbed with generally at least five or six ribs on each compartment: the radii are here very wide, and extend from tip to tip of the compartments, so that their summits are parallel to the basis; they are generally covered by a brownish epidermis, thickly clothed with little spines; the orifice is neatly diamond-shaped; the apices of the opercular valves meet at a common point: these specimens are almost always smaller and younger than the granulated specimens. Altogether the specimens in the two opposite states have, in their external appearance, nothing in common, and no one, without careful examination, would ever suspect that they were specifically identical; this, however, was proved by the intermediate forms, and, in one instance, three of the compartments had their surfaces granulated, and were entirely destitute of the radii, whilst the fourth by some chance had been preserved from corrosion, was longitudinally ribbed, and had its epidermis-covered radius fully developed. The difference in the appearance of the opercular valves, in the two states, is simply owing to the degradation of their upper parts in the granulated specimens.

The basal diameter of the largest specimen was one inch, but the height only .35 of an inch.

Scuta, transversely elongated, so that the basal margin is nearly twice as long as the tergal margin: articular ridge very little prominent; articular furrow wide but shallow; adductor ridge very blunt, slightly prominent, sometimes almost absent, almost parallel to the basal margin: there are no distinct crests for the rostral or lateral depressor muscles, but some small irregular pits for the latter. In one young specimen, the lines of growth were crenated, showing a tendency in the valve to become longitudinally striated, as in the allied T. costata. In some young and immature specimens, the basal margin was deeply sinuous.

Terga, small in area, not above half that of the scuta: spur extremely short, broad, placed close to the basi-scutal angle of the valve, so that there is no basal margin on that side of the spur. The lower end and sides of the spur form one uniform curve. Articular ridge barely developed. Crests for the tergal depressores sharp and prominent.

Structure of the Shell and Radii.--The walls are very thick, and the parietal tubes small and numerous; there are sometimes from twelve to fifteen rows of tubes in the thickness of the wall. The tubes in their whole upper part are filled up solidly; and, as we have seen, are often exposed by disintegration. In very young specimens, of that size in which in T. porosa there would be only a single row of parietal tubes, there were here two or three rows. The development of the radii, as we have seen, is very capricious; the sutures even sometimes being lost. The radii, when developed, are broad, square on the summit, and covered by brownish hirsute epidermis: internally they are formed of tubes like those forming the parietes; in this respect differing from all the species except the following, T. costata. The tubes in the radii run obliquely down towards the basis; instead of in a transverse line, directly towards the opposite compartment, as might have been expected from the structure of the radii in Balanus. The alæ have their edges finely crenated. The sheath in all the specimens which I have observed is colourless; its lower edge is not free. The corium entering the parietal tubes, and lining the opercular valves, the mouth, and the anterior cirri, is generally of an extremely dark purple colour.

The Basis is entirely membranous, in which respect this species differs from all the others in the genus.

Mouth: all the trophi are unusually hairy or spinose. The labrum is deeply notched and apparently destitute of teeth on the crest. The palpi are club-shaped or enlarged at their extremities. The mandibles have the fourth tooth rudimentary.

In the Cirri, the second and third pairs are remarkably short and blunt. In one specimen the two rami of the first cirrus had respectively six and sixteen segments; those of the second, six and seven; those of the third, seven and seven; and those of the sixth cirrus twenty rather elongated segments, with a small tuft of spines between each main pair of spines.

Affinities.--This species differs from all, in its membranous basis, and in its transversely elongated scuta. It resembles T. costata, and differs from all the other species, in its radii (when developed) being square on the summit, and in being formed of tubes,--in the smallness and number of the parietal tubes,--in the absence of crests on the under side of the scuta for the rostral and lateral depressor muscles,--in the shortness and rounded form of the spur to the terga,--and, lastly, in the club-shaped palpi and small size or absence of the fourth tooth in the mandibles. T. purpurascens differs from T. costata in those points, namely, in its membranous basis and transversely elongated scuta, in which it differs from all the other species, and, moreover, in its scuta not being plainly striated longitudinally, in having more ribs on the external surface of the parietes of its shell, and in having only three pairs of main spines on the three posterior cirri.

5. TETRACLITA COSTATA. Pl. 11, fig. 2 a-2 c.

Shell depressed, whitish, generally with ten very prominent longitudinal ribs: radii broad, with their summits parallel to the basis: basis calcareous: scutum externally striated longitudinally: tergum with the spur short and rounded.

Hab.--Philippine Archipelago, Mus. Cuming. Attached to various shells, within the tidal limit.

General Appearance.--Shell whitish, probably tinged, when alive, with reddish-purple; depressed; surface perfectly preserved, smooth, but having longitudinal very prominent ribs, almost invariably ten in number; namely, three on both the rostrum and carina, and two on the two lateral compartments, with ten corresponding projections round the basal margin. Orifice passing from rounded-trigonal to diamond-shaped. The radii are very broad and square at the summit, and extend from tip to tip of the compartments. Basal diameter of largest specimen under half an inch, generally from .3 to .4 of an inch.

Scuta, of the usual sub-triangular shape, and not transversely elongated, as in T. purpurascens. External surface striated longitudinally; in many specimens there is a medial depression, or a row of very small pits, such as occur on the scuta of Balanus trigonus and lævis. The adductor ridge is moderately developed, and runs nearly parallel to the occludent margin; there are no crests for the rostral and lateral depressor muscles.

Terga: these in area equal two thirds of the scuta: the spur is short and rounded, and placed as described under T. purpurascens; but the articular ridge seems to be more prominent than in that species.

Structure of the Shell and Radii.--The parietal tubes are small, and very numerous, as in T. purpurascens. The radii are wide, square on the summits, but not so conspicuously covered by hirsute epidermis as in that species. Internally, the tubes forming the radii are smaller, and run more transversely than in T. purpurascens, that is in the normal course, as in Balanus. The edges of the alæ are nearly or quite smooth. The Basis is as distinctly calcareous, as in the other species of the genus.

Mouth: the trophi are not so hairy as in T. purpurascens; the labrum seems destitute of teeth; the palpi are club-shaped at their ends; the mandibles have only three teeth. The second and third cirri are not so short and blunt relatively to the others as in T. purpurascens. In the posterior cirri, the elongated segments carry four main pairs of spines, between which there is no intermediate tuft of fine spines.

The Affinities of this species have been fully pointed out under the last and closely related species. In external appearance, T. costata can at first hardly be distinguished from those young and pale-coloured varieties of T. purpurascens, which have their external surface not corroded, and their radii well developed.

6. TETRACLITA VITIATA. Pl. 11, fig. 3 a-3 e.

Shell white, generally tinged in the upper part with pink; surface irregular: parietal tubes very irregular: radii moderately wide, with their summits oblique: alæ with very thick crenated sutural edges: tergum with the spur not joined to the basi-scutal angle; spur with its extremity equably rounded.

Hab.--Philippine Archipelago; Barrier Reef, (Raine's Islet), Australia; Mus. Cuming and Stutchbury. Attached to massive corals, to coral-rock, to a Tridacna, and to Tetraclita cœrulescens.

General Appearance.--Shell conical, moderately steep: white, generally with a tinge of pinkish-purple in the upper part, owing to the exposure of the tips of the upfilled parietal tubes. The lower part of the surface is generally well preserved, and is formed by very irregular, branching, longitudinal, slightly prominent, ridges. Radii of moderate width, with their summits oblique. Orifice rather large, rounded trigonal.

Scuta, rather narrow, with the upper part acuminated: the external surface generally much disintegrated, and marked with some irregular blotches of dark red. Articular ridge not prominent; articular furrow rather deep: adductor ridge, distinct from the articular ridge, pretty well developed, as are the crests for the rostral and lateral depressor muscles. In young and well preserved scuta, there is an external, medial, hyaline band, corresponding with the hollow under the adductor ridge, and caused by the thinness of the valve along this line.

Terga: externally, the carinal half is longitudinally and very feebly striated. Internally, the articular furrow is very wide, but shallow, and of unusual length, owing to the preservation of the upper part of the valve; the articular ridge is not prominent. The spur does not actually join, as in all the foregoing species, the basi-scutal angle, but is separated from it by a short piece of basal margin; its two sides are more nearly parallel than is usual, and the end is regularly rounded. It is always rather narrow, though the width varies considerably (fig. 3 d, 3 e). It extends in the same straight line with the middle of the articular furrow. The terga, though not possessing any striking characters, differ considerably in appearance from those of the other species.

Structure of the Shell and Radii.--The parietal tubes are remarkable from their irregular shapes, and unequal sizes (fig. 3 b),--hardly two resembling each other. Sometimes a single elongated tube will reach across the whole thickness of the walls. The septa between the tubes are rather thick and rugged. The tubes are generally darkly coloured from the adhering corium; they are solidly upfilled, but only in the uppermost part, by dark chocolate-red shelly matter. The radii are formed by irregularly branching ridges, with the interspaces filled up solidly. The square edges of the alæ are much thicker than in any other species, and are furnished with transverse ridges, which are sometimes slightly branched. The inner lamina of the walls near the basis, in most of the specimens, is irregularly and longitudinally ribbed, the ribs being longitudinally striated. The sheath and the upper part of the inner lamina of the parietes are clouded with chocolate-red.

The animal's Mouth and Cirri were ill-preserved; but I was able to make out that the labrum had some strong teeth, and that the mandibles were furnished with five teeth, a greater number than in any other species. The palpi had parallel sides as usual. In the sixth cirrus, the segments had four pairs of main spines, instead of the usual number of three.

Affinities.--This species does not appear to be particularly related to any other one: perhaps it is rather nearer to the two following than to the foregoing species. The irregular parietal tubes, thick-edged alæ, form of terga, five teeth to the mandibles, and four pairs of spines to the segments of the posterior cirri, are its chief characteristics.

7. TETRACLITA CŒRULESCENS. Pl. 11, fig. 4 a-4 d.

LEPAS CŒRULESCENS. Spengler. Skrivter af Selskabet, 1 Bind., 1790.[111]

[111] The longitudinally folded walls, as described by Spengler, the blue colour, the habitat, namely, associated with B. tintinnabulum from the East Indies, and more especially the expression "Valvulæ operculi cardine dentato mobilis," apparently referring to the highly prominent articular ridge of the scutum, leave little doubt on my mind that I have rightly named the present species.

Shell with the upper part tinged greenish-blue, longitudinally ribbed: radii moderately wide, with their summits oblique: scutum with a small adductor and extremely prominent articular ridge, united together and so forming a small sub-cylindrical cavity: tergum with the spur not joined to the basi-scutal angle.

Hab.--Philippine Archipelago, attached to Balanus tintinnabulum; attached to a ship's bottom, and to Balanus tintinnabulum, both from the Pacific Ocean; attached to a massive coral, and associated with T. vitiata, and therefore from the tropical eastern seas; Mus. Brit., Cuming, Stutchbury.

General Appearance.--Shell conical, sometimes depressed; surface with rather broad, smooth, longitudinal ridges; whitish, with the upper part greenish-blue, sometimes very feebly tinted with pink; radii white, or mottled with blueish-green, or with pink. When the outer lamina of shell has been corroded, the upfilled parietal tubes, of a dull blueish-gray colour, are exposed. The radii are moderately wide, with their summits very oblique. In basal diameter, one specimen was 1.8, and another 1.5 of an inch.

Scuta, externally furrowed very slightly in a longitudinal direction, causing the lines of growth to become a little sinuous. The valve is strong and thick; and the epidermis, when preserved, is hirsute with spines. The articular ridge is extraordinarily prominent; it projects, as measured from the external surface of the valve, to an amount equalling half the width of the valve in its widest part. The adductor ridge is very short, and is united to the bottom of the articular ridge, thus forming a small, nearly cylindrical tube, which runs up to near the apex of the valve. The inflected occludent margin is broad and coarsely toothed. The crests for both depressor muscles are not very prominent. When the scuta and terga are articulated together, owing to the great projection of the articular ridge of the scutum, its upper part is separated from the tergum (fig. 4 b), by a remarkably wide and deep, fissure-like hollow. The scutum, in some distorted specimens from a ship's bottom, was narrow in proportion to its ordinary breadth.

Terga.--These are large. Externally, there is a broad, longitudinal depression, bounded on each side by a ridge. The carinal half is feebly striated longitudinally. A large upper portion (fig. 4 b) projects freely, and stands, when the two valves are articulated together, above the apex of the scutum, but does not form a beak as in T. porosa. Internally, the tergal margin is widely inflected; the articular furrow is very deep, but the articular ridge is not prominent. The spur is not very broad; it is separated from the basi-scutal angle by a small space of basal margin, which forms a straight line with the basal margin on the opposite side of the spur. The end of the spur is truncated, and is parallel to the basal margin.

Structure of the Shell and Radii.--The walls are thick: the parietal tubes are rather large and regular; they become solidly filled up in their upper parts. The sutural edges of the radii are formed by unusually narrow, sinuous ridges, sending off delicate denticuli on each side: the interspaces between these ridges are solidly filled up. The crenated edges of the alæ are rather thick. Neither the mouth nor the cirri offer any noticeable character; but I may observe, that, in the mandibles, the third and fourth teeth are close together; and that, in the three posterior cirri, the tufts of small spines between the main pairs are small.

Affinities.--This species is very distinct from the others, with the exception of the following T. radiata, to which it is in several respects allied. The under side of the scutum, with its great articular ridge, and the cylindrical tube formed by the union of the latter with the short adductor ridge, affords the most noticeable character.

8. TETRACLITA RADIATA. Pl. 11, fig. 5 a-5 d.

CONIA RADIATA.[112] De Blainville. Dict. Sc. Nat., 1816-1830, Pl. 164, fig. 5, 5 a, (sine descript.)

---- LYONSII. G. B. Sowerby. Genera of Recent and Fossil Shells, Plate, 1823, (sine descript.)

[112] The synonymy of this species is complicated. De Blainville gives no description under the article Conia, published in 1818, or in the vol. published in 1822; but I believe, from the figures of the opercular valves, that I have correctly identified this species with his C. radiata. Mr. Sowerby gives no description of C. Lyonsii, or any figure of the opercular valves, but his drawing of the shell is much better than de Blainville's, and I believe it is the same species. Whether de Blainville's or Sowerby's plate appeared first I cannot ascertain. In the second edition of Lamarck, Conia radiata of Blainville is given as a synonym to Balanus radiatus of that work; but this is quite erroneous. I may add that if de Blainville's name does not apply to the present species, it must to T. cœrulescens, and as the latter is the older name it will be permanent. In this case, T. radiata might be allowed to stand as my own name, considering that Mr. Sowerby's figure is imperfect and is not accompanied by any description. At first I thought that the present species might be the Lepas mitra of Spengler, ('Skrivter af Naturhist. Selskabet,' 1790, Tab. 6, fig. 5), but the parietes are not described as porose; and the folds on the walls are too broad; on the other hand, his description of the opercular valves makes me think this may be the same species.

Shell white, with numerous approximate longitudinal ribs: radii broad, with their summits slightly oblique, internally porose: tergum with the articular ridge extraordinarily prominent, with the spur not joined to the basi-scutal angle.

Hab.--West Indies, adhering to Balanus eburneus and to Lepas anserifera. New South Wales, adhering to Tetraclita porosa. Attached to Balanus tintinnabulum, on a ship's bottom from Sumatra; not rarely attached to Balanus tintinnabulum on ships' bottoms; Mus. Brit., Stutchbury, and Cuming.

General Appearance.--Shell white, rather steeply conical, with numerous, approximate, rather narrow, longitudinal, rounded ribs on the walls: in a specimen half an inch in diameter, there were from eight to twelve ribs on each compartment. The outer lamina of shell seems always well preserved. Orifice rounded, trigonal. Radii white, smooth, broad, with their summits only slightly oblique. I have seen one specimen 1.2 in basal diameter, but quarter of an inch is a common size, and very young specimens are unusually frequent in collections.

Scuta broad, externally not striated longitudinally. The articular ridge is prominent, and the furrow deep, but not in so great a degree as in T. cœrulescens. The adductor ridge is only slightly prominent; it extends upwards only a little way above the lower end of the articular ridge, and does not form with the latter a cavity. There are no crests for the rostral depressor muscle, but there is a little pit, formed by the folding over of the occludent margin.

Terga.--These valves, when articulated with the scuta (fig. 5 b), project above them to an extraordinary degree, and are separated from them by a deep, fissure-like hollow, caused by the remarkable prominence of the articular ridge of the terga. The upper part of the tergum is not beaked, and does not project freely much above the sack. The valve is large; externally there is a rounded longitudinal furrow. The tergal margin is broadly inflected. The articular furrow is deep, and the articular ridge far more prominent than in any other sessile cirripede, for it projects, as measured from the outside surface, more than half the width of the valve; and consequently the valve, when viewed vertically from above, almost appears as if formed by the union of three plates, viz., the articular ridge, and the outside surface on each side of the spur. The spur is of moderate width, with the corners rounded: it is placed near, but not close to the basi-scutal angle, so that there is on this side a small portion of basal margin, forming nearly a straight line with the margin on the carinal side. In some young specimens, about the tenth of an inch in diameter, from the West Indies and from New South Wales, the spur (the position of which I found varied a little in some other specimens) was placed nearly in the middle of the valve, and very nearly at right angles to the basal margin; it is possible that these may be a distinct species, but without larger specimens to judge from, I think it more probable that this difference in the tergum is due to variation and youth.

Structure of Shell and Radii.--The parietal tubes are commonly elongated in the ray of the circle: the septa are rather thick, and strongly crenated at their basal edges. The inner lamina of the walls is strongly ribbed longitudinally. The broad radii have their sutural edges formed by ridges, with numerous and closely approximate denticuli: the interspaces between the main ridges are not soon filled up, and at the bottom, each interspace usually terminates in a pore or tube; so that the radii are not solid, as in most of the foregoing species, but porose. The alæ have their edges crenated.

Basis, calcareous, of unusual thickness; the inner, or upper surface, is striated from the centre in rays, corresponding with the ribs on the inner lamina of the walls. This striated or furrowed structure in the basis, shows a tendency to its becoming tubular or porose, as may be inferred from analogous cases in Balanus.

Animal's body unknown.

Affinities.--This species is rather more closely allied to the last than to any other. There is a close analogy in the peculiar manner in which the scuta and terga are articulated together in the two species: in this species it is effected by the great development of the articular ridge of the tergum, and in T. cœrulescens by that of the scutum. The internally striated calcareous basis, and the internal tubular interspaces between the denticulated ridges of the radii, are peculiar characters. The white colour, the narrowly and closely ribbed parietes, and the broad radii, give this species an aspect, by which it can be easily recognised.

4. Genus--ELMINIUS.

ELMINIUS. Leach. Zoological Journal, vol. 2, July, 1825.

Compartments four: parietes not porose. Basis membranous.

Distribution, Southern temperate seas.

General Appearance.--Shell conical, with a strong tendency in most of the species to become cylindrical: orifice generally large. Walls either thin and smooth, or thick and plicated longitudinally. Colours various, pale purple, greenish, white, and, in E. plicatus, owing to the exposure of an intermediate lamina of shell, bright orange-yellow. Radii, either of considerable width, with their summits oblique and rounded, as in the first two species of the genus, or very narrow, as in the last two species. Elminius plicatus is the largest species, and is sometimes one inch in basal diameter. The outer surface of this latter species is occasionally much corroded.

Scuta: these are of the usual shape; in E. Kingii and modestus there is no adductor ridge and no crests for the depressor muscles; in E. plicatus and simplex, on the other hand, there is a well developed adductor ridge and crests for the lateral depressor muscles; in some individuals, also, of E. plicatus there are small crests for the rostral depressores.

The Terga are remarkable for their variability in all the species; in many specimens of E. Kingii and modestus the basal margin on the carinal side of the spur is deeply hollowed out. The width and acumination of the spur varies in all the species. In E. plicatus and simplex this valve is remarkably like that of Tetraclita porosa. In some specimens of E. Kingii the terga and scuta are firmly calcified together.

Structure of the Parietes and Radii.--As in Tetraclita, the two lateral compartments are necessarily broad. The parietes are never porose, but consist, in appearance, of a single layer of shell. In E. modestus the basal internal edges of the parietes are smooth, but in the other species they are striated longitudinally with short ridges, or sometimes with sub-cylindrical projections. In those specimens of E. plicatus, which have externally suffered much corrosion, the walls have been rendered extremely thick, by the inward production of these ridges or plates; and in this case the ridges are not confined to the basal edges, but extend upwards close to the sheath. The basal surfaces of the walls in these latter specimens resemble those of Chelonobia, but the walls in that genus have an internal lamina, which here is not the case. The radii are wide in E. Kingii, and of moderate width in E. modestus, with their summits oblique and smoothly rounded, and their sutural edges not in the least crenated. In E. simplex they are extremely narrow, smooth-edged, and rounded: in E. plicatus they are narrow, and in this species alone the sutural edge is sinuous, and sends inwards short ridges or teeth. The alæ, in all the species except this last, are likewise smooth-edged. The lower edge of the sheath depends, more or less freely, in all the species, except in E. Kingii.

Basis, membranous in all four species. In E. modestus, the true basal membrane is extremely thin, and is divided into concentric slips: on its inner surface there are attached numerous cement-ducts, varying from 1/3000 to 1/2000 of an inch in diameter, repeatedly trifurcating, rarely forming hexagonal or quadrangular loops, and with the branches placed approximately parallel to each other. Beneath the true basal membrane there is a complicated layer of cement, in the form of a network, or of separate tubes, or in beads and patches. In E. Kingii, the basal membrane presented a wonderfully complicated appearance, in part due to the cement forming a mass of inosculating fibres; many of these fibres seemed to end in circular discs of cement.

Neither the Mouth or Cirri offer any noticeable generic characters, as distinct from Balanus and several other genera. The Branchiæ, in E. plicatus, are well developed and moderately plicated. In E. modestus they are small, not plicated, but with a rounded sinuous margin: in a specimen having a basal diameter of 25/100, the branchiæ in total length were only 4/100 of an inch. At the bottom of the sack I observed some inwardly pointed, tapering filaments, such as occur in Balanus. In this same species I measured the ova, which were unusually elongated, being 19/2000 in length; I may add, that the probosciformed penis was actually thrice the length of the animal's body in some small but mature specimens (with ova), having a shell with a basal diameter of 16/100 of an inch.

Distribution and Habitats.--This genus is remarkable, inasmuch as it is not distributed over the whole globe: three of the species occur very commonly on the shores of New South Wales, Van Diemen's Land, and New Zealand; not extending, as far as I can judge, much north of Sydney: the fourth species is confined to South America, ranging from the Falkland Islands and Tierra del Fuego, as far north as Chiloe. Elminius, therefore, appears to be strictly a southern genus. Elminius Kingii and modestus represent each other on the American and Australian continents; so I believe E. plicatus, in New Zealand, represents E. simplex in New South Wales and Van Diemen's Land. The species are all attached to tidal rocks and shells. E. Kingii is sometimes attached to floating wood. At the Falkland Islands, the last-mentioned species adhered to some rocks, in a running brook of fresh water, at most eighteen inches under high-water mark, so that for the greater part of each tide it was exposed to absolutely fresh water. At Sydney I found E. modestus adhering to oysters in a muddy lagoon, almost separated from the sea, and apparently very unfavorable for cirripedes.

Affinities.--This genus can be distinguished from Tetraclita only by the four compartments not being porose, and by the basis being always membranous; whereas, in Tetraclita purpurascens alone it is membranous. Elminius Kingii and modestus, on the one hand, are closely allied together, as are E. simplex and plicatus on the other hand. The last-named species, in the characters of its opercular valves and in its shell, comes nearest to Tetraclita. In T. rosea we have seen that there is only a single row of parietal tubes, and the outer lamina of the shell is strengthened (as, indeed, it is in most of the other species of the genus, and in Balanus) by small longitudinal plates or ridges, which are similar and homologous to those on the internal basal edges of the parietes in three of the species of Elminius; so that the difference in the structure of the parietes, in Tetraclita and Elminius, is small.

1. ELMINIUS KINGII. Pl. 11, fig. 6 a-6 e.

ELMINIUS KINGII. J. E. Gray. Zoological Miscellany, p. 13, 1831.

---- LEACHII. King and Broderip. Zoological Journal, vol. 5, 1832-1834, p. 334, and appendix to King and Fitzroy's Voyages.

---- ---- G. B. Sowerby. Genera of Recent and Fossil Shells, Plate.

Shell smooth, gray or dirty white: radii broad, smooth-edged: scutum without an adductor ridge; tergum with the spur distinct from the basi-scutal angle: scutum and tergum sometimes calcified together.

Hab.--Tierra del Fuego, Falkland Islands, Chiloe. Attached to tidal rocks and sometimes to floating timber; Mus. Brit., Darwin, &c.

General Appearance.--Shell fragile, either steeply conical with a large orifice, or sub-cylindrical; surface smooth, grayish or white, with large portions covered by pale brown epidermis. Radii broad with their summits oblique, smooth, slightly arched, exhibiting a large surface of the alæ. The alæ usually have their summits much less oblique than those of the radii; the portion added during diametric growth is of a dead white colour. The growth ridges on the scuta are very little prominent, and are crossed by a very obscure band of blueish-gray. The largest specimen which I have seen was .8 in basal diameter, and the longest cylindrical variety .55 of an inch in height.

The Scuta are remarkable for not having any adductor ridge or crests for the depressor muscles; the articular ridge is prominent, but it is short, not extending down half the valve. I have mentioned under the genus, that in many specimens at the Falkland Islands the scuta and terga were calcified together.

The Terga are rather small: the basal margin on the carinal side of the spur is always hollowed out, but to a very variable degree, as may be seen in the three figures (6 c-6 e); this margin is generally dentated with one or two little points; and an inner lamina of shell sometimes depends beneath the outer lamina, to which the opercular membrane is attached, as may be seen in the figure (6 d) of the external surface of the valve. The crests for the depressor muscles are well developed. The tergal margin is broadly inflected, and the articular ridge prominent, making the articular furrow deep. The spur is rather narrow, and is either (6 d, 6 e) bluntly or sharply pointed. The basal margin on the scutal side of the spur, is hollowed out, but to a variable depth.

Structure of the Parietes and Radii.--The parietes are thin; at their internal basal edges they are finely striated in longitudinal lines. The radii are solid, with quite smooth edges; they are generally covered by the epidermis. The sutural edges of the alæ are likewise smooth, these are added to largely during the diametric growth; and their summits, as already stated, are much less oblique than the summits of the radii. The internal surface of the shell is smooth, and is tinted pale dull purple. The lower edge of the sheath can hardly be said to be free. The carinal margins of the compartments project a little inwards.

Mouth: the labrum is deeply notched, and supports five little teeth on each side; the palpi are thickly clothed with spines on their inner sides; the mandibles have five or only four teeth: the maxillæ are notched, and the outer maxillæ bilobed.

Cirri: the first pair has one ramus nearly twice as long as the other. The three posterior cirri are elongated, and each segment supports five or six pairs of long spines, with a few minute intermediate bristles.

2. ELMINIUS MODESTUS. Pl. 12, fig. 1 a-1 e.

Shell folded longitudinally, greenish or white: radii of moderate breadth, smooth edged: scutum without an adductor ridge: tergum narrow, with the spur confluent with the basi-scutal angle.

Hab.--New South Wales; Van Diemen's Land; New Zealand; very commonly attached to littoral shells and rocks; associated with Balanus trigonus and vestitus; Mus. Brit., Cuming, Stutchbury, Darwin.

General Appearance.--Shell conical, generally rather steep, occasionally depressed: walls longitudinally folded, sometimes very deeply, sometimes only to a slight degree: colour dull greenish or white. Radii of moderate width, with their summits very oblique, smooth and slightly arched: alæ much exposed, with their summits less oblique than those of the radii: the portion added to the alæ during the diametric growth differs much in appearance from the other portion. The scuta have the growth ridges but little prominent; they are crossed by a faint longitudinal band of gray. The largest specimen out of the many which I have seen, was under .4 of an inch in basal diameter.

Scuta, destitute of an adductor ridge and of crests for the depressor muscles: the articular ridge is moderate; but the articular furrow is rather wide: the internal occludent margin is much thickened. The Terga are narrow and small; they are somewhat variable in shape, caused by the degree to which the basal margin is hollowed out (fig. 1 c-1 e), and likewise by the extent to which the upper end of the valve has been worn away. No spur is apparent, for it is confluent with the basi-scutal angle of the valve. The articular ridge is very prominent, and runs down to the basi-scutal angle; and as the valve in this part is extremely narrow, with the spur not developed, it here assumes a channelled structure. The basi-carinal corner of the valve is furnished with rather feeble crests for the depressor muscles, and in those varieties in which the basal margin is much hollowed out, this part is remarkably narrow.

Structure of the Parietes and Radii.--The internal basal edges of the parietes and the sutural edges of the radii and alæ, are all smooth. The lower edge of the sheath depends freely. In the green varieties the colour is most distinct on the internal surface of the shell. The four compartments separate very easily when the shell has been ill preserved in spirits, or after a very short immersion in caustic potash.

Mouth, as in E. Kingii, excepting that there are only three teeth on each side of the notch (which is deeper) on the labrum. The cirri resemble those of E. Kingii; the segments in the sixth pair are equally elongated, and bear five or six pairs of spines.

Affinities.--This species is closely allied to its South American representative E. Kingii; the differences consist in its smaller size, often greenish colour, more folded walls, and narrower radii: the internal basal edges, also, of the parietes are here smooth, instead of being striated, as in E. Kingii. The terga present even more obvious differences, in their narrowness, channelled under surface, and in the absence of the spur, or more properly in its confluence with the basi-scutal angle of the valve.

3. ELMINIUS PLICATUS. Pl. 12, fig. 2 a-2 f.

ELMINIUS PLICATUS. J. E. Gray. Appendix to Dieffenbach's Travels in New Zealand, p. 269, 1843.

Shell deeply folded longitudinally, corroded, coloured in parts orange: radii very narrow, with their edges sinuous, and slightly dentated: scutum having an adductor ridge.

Hab.--New Zealand; New South Wales(?). Attached to rocks, often coated by Chamæsipho columna; Mus. Brit. and Cuming.

General Appearance.--Shell tubulo-conical, or conical, rarely depressed; strong, rugged, coloured in parts bright orange; deeply plicated longitudinally, but with the upper parts corroded and smooth. Orifice large. The sutures are indistinct and almost obliterated; the radii, when most developed, are narrow. Some specimens have their whole surface deeply corroded; in which case they are finely striated longitudinally, or pitted, and are of a gray or brown colour. The largest specimens are one inch in basal diameter, but one depressed specimen was 1.3 in diameter; another was rather under one inch in diameter, and one inch in height.

Scuta; beginning with the common tubulo-conical and not much corroded specimens, the valve (fig. 2 c) is moderately elongated, but in a rather variable degree. A prominent adductor ridge runs, from a little above a middle point of the basal margin, along the slightly prominent articular ridge: the articular furrow is moderately wide. There are distinct crests for the lateral depressores. In the conical, corroded specimens, the scuta (fig. 2 e) are considerably broader, with the articular ridge much more prominent, and the furrow wider: in one such specimen, there were crests for the rostral depressor muscle.

The Terga, in the commoner variety, resemble those of Tetraclita porosa; the spur adjoins the basi-scutal angle of the valve: the articular ridge is moderately prominent, and the furrow moderately deep. The valve is beaked, with an unusually large internal tube for the thread of corium: the beak, however, is often worn away. In the depressed much corroded specimens, the terga (fig. 2 f), like the scuta, are broader and shorter than in the commoner variety; and the spur more especially is broader. The scutal margin is much more widely inflected, and the articular ridge much more prominent; consequently the articular furrow is much deeper.

Structure of the parietes and radii.--The orange or yolk-of-egg colour, which is so conspicuous a character in the present species, is due to a layer of shell between the inner and outer lamina, and is exposed only by the corrosion of the latter. Hence the very base of the shell is not of this colour; nor are the uppermost and still more deeply corroded portions, for here the orange-coloured layer has been removed. The sheath is orange-coloured, and the operculum, to a certain extent, is similarly tinted. The epidermis on the parietes, where preserved quite close to the basis, supports remarkably strong spines, about 1/100th of an inch in length. The basal internal edges of the walls are rather coarsely striated with irregular short ridges and sub-cylindrical points; and the walls in most of the specimens are regularly and deeply folded, which, with the little ridges, gives the appearance represented in fig. 2 b, Pl. 12. I have stated, under the Genus, that in the corroded and depressed specimens, the walls are rendered extremely thick by the inward production and upward extension of these same ridges and points; the under surface of the shell acquiring almost the appearance of Chelonobia caretta. The Radii are often not developed, even the sutures being obscure; when most developed, they are narrow, with the outer lamina along the growing edge sinuous, giving to the sutures a crenated appearance. The sinuosities on the growing edge generally send inwards short ridges or septa, like those on the sutural edges of the radii in most Balanidæ, but of which there is no trace in the other species of Elminius. In very minute, colourless specimens, about the 1/20th of an inch in diameter, the radii are quite smooth-edged. The alæ have their edges strongly crenated. The lower edge of the sheath depends freely.

Mouth: the labrum shows some tendency to be bullate; the notch is broad and shallow: the palpi have a thick brush of bristles on their inner sides. The mandibles have four or five teeth. In the maxillæ, the upper spines above the broad notch, are very strong. In the outer maxillæ, the two lobes are widely separated.

Cirri: in the first pair, one ramus is about one fifth longer than the other. In the third pair, the posterior ramus is one fourth longer than the anterior ramus, and its terminal segments are tapering, each having a single circle of bristles: the other segments, and those of the shorter ramus, support many coarsely pectinated spines. In the sixth cirrus, the segments are protuberant in front, and carry four pairs of stout spines, with a tuft of fine bristles between them.

Affinities.--This species differs considerably from the first two of the genus. In several characters it approaches nearer than the other species to Tetraclita, especially to T. porosa;--namely, in the scutum having an adductor ridge and crests for the lateral depressores, in the whole form of the tergum, in the thick walls liable to much corrosion, in the narrow radii, and in their edges, as well as those of the alæ, being crenated; and, lastly, in the character of the cirri, more especially of the third pair, with its coarsely pectinated spines. It also approaches, in all its characters, Balanus imperator and flosculus.

4. ELMINIUS SIMPLEX. Pl. 12, fig. 3.

Shell ribbed longitudinally, dirty white; radii extremely narrow, smooth-edged; scutum having an adductor ridge.

Hab.--New South Wales (Sydney and Twofold Bay); Van Diemen's Land; tidal rocks, often attached to other Cirripedes, and associated with Balanus nigrescens, Tetraclita purpurascens, Catophragmus polymerus; Mus. Brit., Cuming, Stutchbury, and Darwin.

This species, of which I have seen specimens from the above three localities, all exactly agreeing with each other, is perhaps the Australian representative of E. plicatus, which seems to be confined to New Zealand.[113] In all essential points it comes so near that species, that I shall make the greater part of my description comparative.

[113] I am bound to state that I have seen two specimens of E. plicatus marked Sydney, and one marked Moreton Bay, but in both cases the collectors had visited New Zealand, so that a wrong habitat by mistake might easily have got attached to the specimens in question.

General Appearance.--In external appearance there is considerable difference from E. plicatus, for E. simplex is generally of a regular conical shape, of a dirty-white colour, with the surface well preserved, having moderately wide, not very prominent longitudinal ribs. The orifice is rather small and pentagonal. The radii are extremely narrow or linear, with quite smooth edges; the sutures, however, are always very distinct, and in the upper part, the alæ are generally rather widely exposed, as viewed from the outside. The largest specimen which I have seen was .7 of an inch in basal diameter.

The opercular valves are closely similar to those of E. plicatus, but the scutum is generally a little more elongated, and the articular furrow not so deep: in accordance with this last fact, the articular ridge in the tergum is not so prominent as in E. plicatus; but we have seen that these several characters are highly variable in E. plicatus. The slope of the basal margin of the tergum towards the spur varies in the present species, in a strictly analogous manner, as it does in Tetraclita porosa.

Structure of the Parietes and Radii.--The parietes are not so thick as in E. plicatus; internally they are tinted pale purple; when broken transversely, a row of microscopically minute orange-coloured dots can generally be distinguished between the outer and inner laminæ; and these evidently represent the orange-coloured layer in E. plicatus. The sheath also exhibits a faint tinge of orange. The radii are very narrow, and are quite smooth-edged, differently from in E. plicatus. The edges of the alæ barely exhibit a trace of being crenated.

In the body I could perceive no difference from E. plicatus, excepting that in the third pair of cirri the two rami are like each other, and do not support any coarsely pectinated, only serrated, spines; but after what we have seen on the variability of these very same characters in Tetraclita porosa, I dare not trust to them. The three posterior pairs of cirri, also, seem here to be more elongated in proportion to the others, than in E. plicatus.

Affinities.--It is certain that this species is most closely allied to E. plicatus; but as I have seen many specimens of the latter brought by different persons from New Zealand, and as I have observed in them no approach to the characters of E. simplex, which, in specimens from three localities, also appear to be constant, I have considered the two forms as specifically distinct. The present species differs from E. plicatus, in its white, conical, moderately ribbed, well preserved, smaller shell; and more especially in the orange-coloured intermediate lamina of E. plicatus being here represented only by microscopically minute dots. But the radii being smooth-edged, is the most important differential character, though in E. plicatus, during its earliest growth, whilst still immature and colourless, the radii are likewise smooth-edged.

5. Genus--PYRGOMA.

PYRGOMA. Leach. Journal de Physique, tom. 85, 1817.

BOSCIA. Ferussac. Dict. Classique d'Hist. Naturelle, 1822.

SAVIGNIUM. Leach. Zoological Journal, vol. 2, July, 1825.

MEGATREMA. Ib. Ib.

ADNA. Ib. Ib.

DARACIA. J. E. Gray. Annals of Phil. (new series), August, 1825.

CREUSIA. De Blainville. Dict. Sc. Nat., Pl. 116, 1816-30.

NOBIA. G. B. Sowerby, junr. Conchological Manual,[114] 1839.

[114] The name, Nobia, is given in this work on the authority of Leach, but this must be a mistake, probably caused by some MS. name, (that fertile source of error in nomenclature), having been used.

Shell formed of a single piece; basis cup-formed, or sub-cylindrical, attached to corals.

Distribution, imbedded in corals, chiefly in the tropical seas, round the world.

I feel no hesitation in including the above several genera in one genus. In external appearance the P. monticulariæ (Pl. 13, fig. 5 a), which forms the genus Daracia of Gray, is the most distinct, but it is so intimately allied to the two, indeed to the three, foregoing species, that it cannot be separated from them. Of the first five species, P. grande, conjugatum, and cancellatum, form a graduated series, but with the steps very distinct, the chief difference being in the length of the spur of the tergum; for the fact of the scutum and tergum being calcified together in P. grande and conjugatum, and distinct in P. cancellatum, is certainly unimportant, as may be inferred from what we shall see in comparing together the last four species of the genus, and from what we shall see in Creusia spinulosa. The three above-mentioned graduated species are connected with the last four species of the genus, by several points of resemblance between P. grande and crenatum. The first two species, namely, P. Anglicum and Stokesii, are the most closely related together, and may indeed possibly be identical; these two, in all the characters derived from the opercular valves, resemble Balanus and other ordinary forms, and for this very reason they have some claims to be generically separated from the other species of Pyrgoma; for in these latter, the opercular valves seem to have broken loose from all law, presenting a greater diversity in character than do all the other species of Balaninæ and Chthamalinæ taken together.

General Appearance.--The shell consists of a single piece, generally without any suture, even on the internal surface; and this is the case, at least in P. Anglicum, in extremely young colourless specimens: nevertheless, in some specimens of this very species, and of P. conjugatum, there were traces of two, but only two, sutures on the sheath, one on each side towards its carinal end. The shell is much depressed or actually flat; and I have seen specimens even slightly concave; in P. Anglicum, however, the shell is steeply conical. The outline is generally oval; but in P. monticulariæ it is extremely irregular. The surface is generally furnished with more or less prominent ridges, radiating from the orifice, which is oval and small; sometimes, as in P. monticulariæ, excessively small. The colour is white, or pinkish-purple. Most of the species are small, but I have seen specimens of P. grande three quarters of an inch in diameter in the longer axis, and, including the deep, almost tubular, basis, more than three inches in length or depth.

Opercular Valves.--In three species, viz., P. conjugatum, (Pl. 12, fig. 7 c), grande, and monticulariæ, the scuta and terga, on each side, are calcified together so perfectly, that there is no trace of a suture or line of junction: in P. milleporæ, these valves are generally slightly calcified together, but with the suture distinct. The Scuta differ so much in shape in the different species, that little can be said of them in common: in P. Anglicum and Stokesii they resemble those of Balanus; but in the other species they are much more elongated than is usual, and this is carried to an extreme in the last four species; this elongation is due to a great increase in breadth, as may be inferred from the position of the apex of the valve, and from the direction of the lines of growth. But the two most remarkable characters are, first,--the extraordinary development of the adductor ridge, so that, in P. conjugatum, cancellatum (Pl. 12, fig. 5 c), grande, and crenatum, it extends considerably beneath the basal margin, being produced, in the first two species, at the rostral angle, into a point; at the tergal end of the valve, the adductor ridge, when thus much developed, blends into the articular ridge. The second very remarkable character is the addition of a special ledge along the occludent margin of the scutum, and along the carinal margin of the tergum, which I will call the occludent ledges (limbus occludens), and which serve to close the orifice leading into the sack. The occludent ledge is small in P. grande, and is clothed with thick yellow spines, giving it a brush-like appearance: in P. crenatum and dentatum it is largely developed, the ledge on the scutum being articulated with that on the tergum, as shown in Pl. 13, fig. 4 a, 4 b,--the ledges being here and elsewhere marked by little bristly points. In P. monticulariæ, however, this ledge arrives at its maximum development (Pl. 13, fig. 5 f), the rest of the valve (the scuta and terga being here, as in P. grande, calcified together) being reduced to a mere basal edge or border. Excepting for the adductor muscle, the depressions or crests for the other muscles, both on the scuta and terga, are hardly developed.

Terga: these, as in the case of the scuta, differ so much in shape in the several species, that little can be said of them in common. In P. Anglicum and Stokesii, they are of the normal shape; in P. cancellatum (Pl. 12, fig. 5 d) this, to a certain extent, is likewise the case, but the spur is produced to a quite extraordinary length. In P. grande (Pl. 13, fig. 1 b) there is no distinct spur, and the whole valve is square. In P. milleporæ (2 f) there is no spur, and the valve is arched and triangular. In P. crenatum the spur is broad, rounded, and depressed (fig. 4 b), with the carino-basal portion of the valve reduced to a mere border, barely distinguishable from the great occludent ledge. In P. monticulariæ there is no spur, and the whole valve forms a mere border to the occludent ledge; and, lastly, in P. dentatum, the valve is extremely variable in shape (fig. 3 c, 3 d, 3 f), and on its internal surface (fig. 3 g) there is an inwardly projecting, most singular and anomalous, tooth. Hence we see how wonderfully variable the terga are in this genus.

Structure of the Walls.--The shell consisting, as has been stated, of a single piece, is generally thick. From the close alliance between this genus and Creusia, it is probable that the shell, if examined immediately after the metamorphosis, would be found to show traces of being formed of four compartments. The walls are either solid or porose; their basal margin is formed by strong crenated ridges, answering to the longitudinal septa in Balanus; but these in P. monticulariæ are modified into a very irregular surface. The internal surface of the shell is generally smooth, or only slightly ribbed. The sheath has its lower edge free in P. Anglicum and Stokesii, and in a slight degree in P. milleporæ, but in the other species it is closely attached to the walls. In P. monticulariæ the sheath might easily be overlooked. In P. Anglicum, grande, and crenatum, it descends almost to the basal margin of the depressed shell, and as the opercular valves and membrane are attached to the lower edge of the sheath, the animal's body necessarily comes to be almost exclusively lodged in the cup-formed basis. In P. grande and conjugatum, the lines of growth in the sheath are bent upwards on each side, at points corresponding with the line of union between the scutum and tergum, in a manner I have not seen in any other cirripede; and this sometimes gives the appearance of two lateral sutures. I may here remark, that the manner of growth in Pyrgoma is almost the converse of that in Balanus, Tetraclita, and other allied genera; for in these latter, the basis increases in diameter, and the shell chiefly in height; whilst in Pyrgoma, the shell, from being so flat, increases almost exclusively in diameter, whereas it is the basal cup which is added to in height or depth.

Basis.--This in all the species is more or less regularly cup-formed or sub-cylindrical. In P. grande it penetrates the coral to a surprising depth; in P. monticulariæ it is irregular in outline, corresponding with the shell. The basis is generally almost wholly imbedded in the coral; but this is not the case with P. Anglicum, in which the basis is generally exserted, as it is in a slight degree in P. grande. The shelly layer forming the basis, in most of the species, is very thin, and is finely plicated owing to its edge folding between the ridges or septa that form the basal edges of the shell; this is very conspicuous in P. cancellatum. The basis is not permeated by pores, except in P. Anglicum. In some sessile cirripedes a cleft, covered only by membrane, may be observed all round between the lower edge of the shell and the basis; a cleft of this nature is rather conspicuous in P. crenatum, so that small portions of the septa on the internal surface of the walls can be seen from the outside. In P. monticulariæ, an analogous structure, developed to an extreme degree, presents a very different and unique appearance; the shell is nearly flat, and the smooth outer lamina does not nearly reach to the circumference, a wide border being thus left exposed, which is roughened (Pl. 13, fig. 5 a, 5 c, 5 d, 5 e) by the exposure of the irregular septa. I have not seen a fresh specimen, but there cannot be a doubt that this border is properly covered by membrane.

Animal's Body.--From some cause, perhaps from the corals in which the species of Pyrgoma are imbedded, long remaining damp, the internal organs are generally badly preserved. I have received, in spirits of wine, only P. Anglicum, but I have examined dry specimens, in a tolerable condition, of P. milleporæ and crenatum. As neither the mouth nor cirri, in these three species, offer any noticeable characters, distinct from those in Balanus or Acasta, my ignorance of these organs in the other six species is not important. In the above three species the labrum is deeply notched, with about three teeth on each side of the notch, except in P. milleporæ, in which the number is six. In all, the mandibles have five teeth, the two lower ones being small: the maxillæ are not notched: the outer maxillæ are bilobed. In the Cirri, the rami in the first pair are very unequal in length, the segments being slightly protuberant in the shorter ramus. On the segments of the posterior cirri there are four pairs of spines in P. Anglicum, and three pairs (of which the second and third are short) in P. milleporæ. At the dorsal basis of the penis there is a small straight projecting point.

Affinities.--The species (with the exception of the first two) are much more distinct from each other, and more easily determined than is usual with sessile cirripedes; it is, however, quite useless to attempt naming the species without disarticulating and cleaning the opercular valves. Although these valves differ so greatly in some of the species from those of Balanus and the allied forms, the genus itself, as a whole, does not differ much, except in the shell not being divided into compartments, and in the basis being cup-formed and not generally permeated by pores,--these latter characters being in common with Acasta. With respect to the absence of separate compartments, it should be remembered, that in the same species of Tetraclita we have individuals with the four compartments distinct and furnished with radii, and other individuals without any trace of a suture externally,--the outer lamina of shell (though not the inner) having become completely confluent all round. At the commencement of this description, when giving my reasons for uniting the several proposed genera into one genus, I gave a sketch of the affinities of the species: I have only to add, that the following sub-genus Creusia is closely, perhaps too closely, allied to Pyrgoma.

Geographical and Geological Distribution.--Most of the species are inhabitants of the hot coral-growing zones, in both the eastern and western hemispheres, but more especially, as it would appear, in the East Indian Archipelago. From the habits of the corals, most of the species must be inhabitants of shallow water. Pyrgoma Anglicum, however, is an inhabitant of deep water on the southern shores of England, whereas at St. Jago, in the Cape de Verde Islands, I myself collected it adhering to a Caryophyllia, within the tidal limits. This same species existed on the shores of England during the Coralline Crag period; and at this epoch it attained a larger size than at present. Two species of the genus, according to Sismonda, are found in the tertiary beds of Piedmont. Mr. Stutchbury, who is so well acquainted with recent cirripedes, informs me that he has for many years examined fossil Secondary corals, in the expectation of finding imbedded, species of this genus or of some allied form, but without success. The same species of Pyrgoma is by no means always confined to the same coral: I have seen P. crenatum on four or five different corals, and P. Anglicum on at least three kinds: on the other hand, I have seen P. milleporæ only on the Millepora complanata (a member, as I believe, of the vegetable kingdom), and P. monticulariæ on a Monticularia from near Singapore.

1. PYRGOMA ANGLICUM. Pl. 12, fig. 4 a-4 c.

PYRGOMA ANGLICA. G. B. Sowerby. (sine descript.) Genera of Recent and Fossil Shells, fig. 7, No. 18, Sept. 1823.

MEGATREMA (ADNA) ANGLICA. J. E. Gray. Annals of Philosoph. (new series), vol. x, Aug. 1825.

PYRGOMA SULCATUM. Philippi. Enumeratio Molluscorum Siciliæ, Tab. 12, fig. 24, (1836).

---- ANGLICA. Brown. Illustrations of Conchology, (2d edit., 1844), Tab. 53, fig. 27-29.

Shell steeply conical, purplish red: orifice oval, narrow: basis permeated by pores, generally exserted out of the coral: scutum and tergum sub-triangular.

Hab.--South coast of England and of Ireland, (12 to 45 fathoms, Forbes and MacAndrew); Sicily; Madeira; St. Jago, Cape de Verde Islands; generally attached to the edge of the cup of a Caryophyllia, in deep water, but at St. Jago within the tidal limits; Mus. Brit., Cuming, Lowe, &c.

Fossil in the Coralline Crag, Ramsholt; Mus. S. Wood.

General Appearance.--Shell steeply conical, slightly compressed, the lower part with rounded, approximate, radiating ribs: colour dull purplish-red: orifice oval, small, and narrow. The basis is not deeply conical, and occasionally is even flat. Generally it stands exserted; but in the Coralline Crag specimens, it is almost wholly imbedded. Externally it is furnished with ribs corresponding with those on the shell. The largest recent specimen which I have seen, from St. Jago, was .22 of an inch in basal diameter; but some few of the British specimens are nearly as large, and one of the fossils from the Coralline Crag a little larger.

The Scuta and Terga are of the ordinary shape of these valves in Balanus and its allies. Scuta triangular, with the basal margin a little curved and protuberant: adductor and articular ridges distinct from each other, moderately prominent: there is a small hollow for the lateral depressor muscle. Terga triangular, with the spur rather narrow, moderately long, placed near, but not confluent with the basi-scutal angle of the valve. The basal margin forms an angle rather above a right angle with the spur. Internally, the articular ridge and crests for the depressor muscles, feebly developed.

Internal Structure of the Shell and Basis.--Internally, the shell is ribbed more or less prominently. The lower edge of the sheath, which is reddish, and extends far down the walls, seems always to project freely. In several specimens there were on each side, at the carinal end of the shell, a trace of a suture, which could be perceived only on the sheath. The basis appears always to be permeated by minute tubes or pores, though these are sometimes rather difficult to be seen.

2. PYRGOMA STOKESII. Pl. 12, fig. 6.

MEGATREMA STOKESII. J. E. Gray. (sine descript. aut figurâ) Annals of Philosophy, (new series), vol. 10, Aug. 1825.

Shell moderately conical, pale-purplish red; orifice oval: basis not permeated by pores, deeply imbedded in the coral: scutum and tergum sub-triangular.

Hab.--Imbedded in the Mycedia (Agaricia) agaricites; therefore from the West Indies;[115] Brit. Mus. and Stutchbury.

[115] I am greatly indebted to Mr. Dana for having named for me the coral in which this species was imbedded, and informing me that it is a West Indian species.

This species comes so close to the last, that I am not sure that I have acted rightly in retaining it, but I think that it is distinct; and in this case, it is the representative, on the other side of the Atlantic, of P. Anglicum of our own side. It will be sufficient to point out the few points of difference. The shell is much more depressed, with the orifice oval, larger, and not so narrow. It is apparently of a paler red, and the radiating ribs perhaps not so prominent. The basis offers the most important difference, being deeply imbedded in the coral; and there is not the least appearance of the thin shelly layer, of which it is composed, being permeated by pores, as, we have seen, is always the case with P. Anglicum. As in this latter species, the sheath here depends freely. The opercular valves are closely similar; but in the scutum, the adductor ridge occupies a rather more central position; and in the tergum, the basal margin is more inclined towards, or forms a greater angle with, the spur: these differences, by themselves, I consider quite insufficient to characterise a species; but conjoined with the flatter shell, the larger orifice, the more deeply imbedded and non-porose basis, they may, I think, be admitted as specific. In dimensions, this species seems to attain a slightly larger size than P. Anglicum, for several specimens were .22 of an inch in diameter.

3. PYRGOMA CANCELLATUM. Pl. 12, fig. 5 a-5 f.

PYRGOMA CANCELLATUM. Leach (!). Encyclop. Brit., Supplement, vol. 3, Pl. 57, 1824.

---- LOBATA. J. E. Gray (!). Annals of Philosophy, (new series), vol. 10, 1825.

CREUSIA RAYONNANTE. De Blainville. Dict. Sc. Nat. (sine descript.), Pl. 116, fig. 7, a, b.

Shell with the circumference generally lobed: scutum elongated, with the adductor ridge descending far below the basal margin, and produced at the rostral end into a square point; tergum with the spur four times as long as the upper part of the valve.

Hab.--Imbedded in a Gemmipora, probably from the West Indies;[116] Mus. Brit. and Cuming.

[116] In this case I am again indebted to Mr. Dana for naming the coral; he informs me that the genus is found in the Pacific and East Indies; the specimen sent he believes is the G. cinerascens.

Appearance and Structure of Shell.--Shell nearly flat, sometimes tinted dull dirty purple, with the surface marked by slight, broad, approximate ridges, the ends of which form considerable projections, giving to the shell, when not too much encrusted by coral, a lobed border. In young specimens (.15 of an inch in diameter) some of the points projected half as much as the semi-diameter of the shell, giving it a radiating appearance. The orifice is oval and rather small, but of variable size. The shell is thick, and, near the outer lamina, is penetrated by pores: the internal surface is smooth. The sheath (fig. 5 b) extends down but a short distance from the orifice; it is closely attached to the walls: the lines of growth, at a point on each side, bend a little downwards (instead of upwards, as in the two following species), and hence the lower edge of the sheath irregularly projects downwards on each side. The basal cup, internally, is plicated, the hollows corresponding with the projecting, longitudinal, parietal septa, which form the lobed border of the shell. The largest specimen which I have seen, was rather above .4 of an inch in diameter.

The Scuta and Terga are not calcified together: they are both much elongated. Scutum (fig. 5 c, 5 e).--For the first time in the genus, or indeed in the family, this valve presents a remarkable character in the adductor ridge being immensely developed, so as to project far below the ordinary basal margin. At the rostral end, it at first appears to project even more than it really does, for the toothed occludent margin is in fact a prolongation of the true valve, as distinct from the adductor plate. Excluding this very narrow, prolonged, occludent margin, the adductor plate projects for a length equalling the rest of the valve. Along the tergal margin, the adductor plate is united to the articular ridge; and at the rostral end, it is produced into a square tooth, whence a square-edged ridge extends on the surface of the plate upwards to the ordinary basal margin of the valve. The exact shape of this adductor plate varies a little, as does the degree to which it is closely attached to the ordinary basal edge of the valve. The valve, as distinct from the adductor plate, is narrow, with the basal margin regularly curved. The articular ridge is very prominent.

Terga extremely narrow, linear, consisting in chief part of the spur, which is fully four fifths of the entire length. Externally (fig. 5 d) the valve is furrowed, with the edges more or less folded in along the spur. The upper or ordinary part of the valve is about one third wider than the spur. The basi-carinal angle is sharp, owing to the basal margin being a little hollowed out. A special plate of shell (fig. 5 f), hollow under its basal edge, runs from the carinal margin to the articular ridge, which latter is situated in the middle of the valve, and against which the articular ridge of the scutum abuts. The spur is central; its end is bluntly pointed. The total length of the tergum rather exceeds that of the scutum, the produced adductor ridge being included in the latter.

Affinities.--Under P. grande I shall make a few remarks, showing that in several characters P. cancellatum and grande are at opposite ends of a short series, with P. conjugatum intermediate between them.

4. PYRGOMA CONJUGATUM.[117] Pl. 12, fig. 7 a-7 c.

[117] Dr. Gray thinks this is the Pyrgoma stellata, of Chenu, ('Illust. Conch.'); it may be so; but the figure given of the shell will do equally well or rather better for the Pyrgomum dentatum of this work, and for some varieties of P. crenatum. Without a careful description of the opercular valves, it is really impossible to recognise, with any approach to certainty, the species of this genus.

Shell nearly flat with approximate radiating ridges: scutum and tergum calcified together without any suture: scutum with the adductor ridge descending below the basal margin, and produced at the rostral end into a point: tergum with the spur about as large as the upper part of valve.

Hab.--Red Sea; Brit. Mus. and Cuming.

Appearance and Structure of Shell.--Shell white, or with a tinge of purple; nearly flat, with moderately prominent, narrow, approximate ridges, radiating from the orifice, which is oval, rather narrow, and not very small. In the largest specimens the ridges are less prominent than in the figure given. The walls are thick, and not at all porose: the sheath extends down almost to the base of the shell, and its lower edge is closely attached to the walls: on each side, towards the carina, there is a trace of a suture, and the lines of growth on the sheath are here a little upturned. The basis is deeply imbedded and internally furrowed; the calcareous layer forming it, is thin. The largest specimen was .4 of an inch in the longer diameter.

The Scuta and Terga (fig. 7 b, 7 c), in all the specimens which I have seen, are calcified together, with no trace of a suture. There is, however, a slight furrow, which, I believe, marks the normal line of separation between the two valves; and in the following description this is assumed to be the case. The Scutum has the adductor ridge greatly developed, so as to project below the ordinary basal margin to a distance as great as the height of the valve. At the rostral end, this adductor ridge or plate is produced into a point; and at the tergal end, it is blended with the articular ridge, and united to the inner face of the tergum. That portion of the scutum which corresponds with the valve in ordinary cases, and alone is externally visible as long as the operculum is united by the opercular membrane to the sheath, is narrow, with the basal margin considerably hollowed out: the occludent edge is formed into thick teeth. The Tergum is elongated, rather exceeding in length the scutum, the latter being measured from the apex to the rostral projection of the adductor plate. The surface of the valve is depressed in the line of the spur, with the basal end of the latter bluntly pointed. A very slight flexure (fig. 7 c) on the basal margin indicates where we may believe the spur to commence, showing that it rather exceeds in length the whole upper part of the valve. The lines of growth obscurely indicate a tendency to the formation of a slight "occludent ledge" along the carinal margin. Traces are just visible of crests for the attachment of the tergal depressor muscles.

5. PYRGOMA GRANDE. Pl. 13, fig. 1 a-1 d.

NOBIA GRANDIS. G. B. Sowerby, junr. (sine descript.) Conchological Manual, fig. 29, 1839.[118]

CREUSIA GRANDIS. Chenu. Illust. Conch., Tab. 1, fig. 2 a, sed non, fig. 2.

[118] It is quite possible that this may be the Balanus duploconus of Lamarck, but with such a character as the following, who can recognise a species? "B. testæ parte supremâ univalvi, indivisâ, convexâ: inferiore turbinatâ, non clausâ: aperturâ ellipticâ. L'exemplaire est sans opercule et incomplet."

Shell moderately convex, nearly smooth: scutum and tergum calcified together without any suture: scutum furnished with a small occludent ledge, with the adductor ridge descending below the basal margin: tergum square without a spur.

Hab.--Singapore and East Indian Archipelago; Mus. Brit., Cuming, Stutchbury; imbedded in two kinds of coral.

Appearance and Structure of Shell and Basis.--The shell is conical, though to a variable degree, and sometimes is much depressed. The surface is smooth, with only traces of narrow approximate ridges. The colour is white, often with a tinge of dark purple. The orifice is oval, and moderately large. The shell and a small portion of the basis usually stand exserted above the coral. The walls are of variable thickness; when thick, the pores, by which they are permeated, are but little apparent; sometimes there is more than a single row of pores. The points of the septa on the basal edge of the shell are small. The internal surface of the shell is smooth. The sheath is closely attached to the walls, and descends nearly to the basis; on each side its lines of growth are slightly upturned. The basis is deeply cup-formed or cylindrical, and in section oval like the shell; it penetrates the coral to a very remarkable depth,--in one instance to three inches. The shelly layer forming it, is thin, finely furrowed, and not permeated by pores. This is the largest species in the genus; one specimen was three quarters of an inch in its longer diameter, and above three inches in length.

The Scuta and Terga are calcified together, without any trace of a suture; the line of junction can be inferred only from the analogy of P. conjugatum, in which species the valves have a more normal character, and are separated by a slight furrow. It may be seen in the figure (Pl. 13, fig. 1 d) of the right and left hand opercular valves, viewed from vertically above in their proper relative positions, how abnormal their appearance is, which is partly caused by the spinose occludent ledges, presently to be described, but chiefly from the carinal margins of the two terga not being straight and parallel, as in all other cirripedes, and therefore not meeting each other, as is usual. In other genera, only the upper part of the carinal margin of the two terga can be opened for the exsertion of the cirri, the lower portion being united by membrane; but here, I have little doubt, from the position of attachment of the adductor muscle (fig. 1 c), so close to and almost on the terga, that the whole length of the carinal margin of the two terga is free or disunited for the protrusion of the cirri. This opening between the two terga evidently cannot be closed, but is probably filled up, and the animal thus protected, by the dorsal surfaces of the curled-up cirri; such, I believe, being likewise the case with some pedunculated cirripedes, as with Conchoderma. The scutum has a large adductor plate, which extends some little way (namely, about one quarter of the height of the valve), below the ordinary basal margin. This latter margin is slightly sinuous, and a little hollowed out towards the tergal corner of the valve. I believe that the ridge, which runs down to the basi-scutal corner of the tergum, though appearing to be part of the scutum, really belongs to the tergum. The adductor scutorum plate is not, as in the last two species, produced into a point at the rostral angle; at the tergal end it blends into the under surface of the tergum. The occludent margin is coarsely toothed. Rather on the under side of this margin and in the upper part, there is a narrow occludent ledge, which extends up beyond the apex of the valve, and thence runs a little way along the carinal margin of the tergum. This ledge is thickly clothed with strong, yellowish-brown spines, and hence appears like a brush. It is remarkable that the cavity for the adductor scutorum muscle is situated almost on the tergum.

The tergum is of large size, and nearly square; it is, in appearance, separated from the scutum by a ridge running up to the apex. The basal margin forms a right angle with the carinal margin, along which latter margin the lines of growth are upturned, and blend into the occludent ledge, which is common to the two valves. There cannot be said to exist any spur, the whole basal margin being almost straight; nevertheless, on close examination, the ridge which in appearance separate the scutum and tergum, may, I think, be safely considered as one side of the spur (which, it should be remembered, has in all ordinary cases a longitudinal furrow or depression), and the other side of the spur is, apparently, very feebly indicated by a slight flexure in the middle of the basal margin. Hence, if the spur had been developed, it would probably have been half as wide as the valve. There are no crests for the tergal depressor muscles.

Affinities.--The present species, with the last two, form an interesting series. Pyrgoma grande and conjugatum, however, are more closely allied to each other than to P. cancellatum. In the scutum, the whole valve is least elongated, with the adductor plate least developed, in P. grande, and most elongated, with the adductor plate most developed, in P. cancellatum. In the outline of the tergum the range of shape is quite remarkable; in P. conjugatum, which stands between the other two species, the spur is rather long, whereas in P. grande there is no spur at all--a very unusual circumstance--and in P. cancellatum, at the other end of this short series, the spur attains a length wholly unparalleled in any other cirripede.

6. PYRGOMA MILLEPORÆ.[119] Pl. 13, fig. 2 a-2 f.

[119] From external aspect I suspect this species to be the Creusia madreporarum, Leach (?), as given in Chenu, 'Illust. Conch.,' Tab. 1, fig. 6. But I feel sure that Leach has nowhere published this name; and it may be observed that Chenu gives it with a mark of doubt. The shell in its imbedded state is only figured; the opercular valves are not given; and no descriptive details are added. Under these circumstances I have not adopted this name; I have, perhaps, been in some degree influenced by the fact that this species, judging from the many specimens examined by me, is never imbedded in madrepores, but exclusively in millepores, so that Chenu or Leach's specific name of Madreporarum is singularly inappropriate.

Shell with the orifice narrowly ovate: sheath dark purple: Scutum much elongated: tergum triangular, convex, without a spur.

Hab.--Philippine Archipelago (Mindoro Island), Mus. Cuming. Mus. Brit., Stutchbury, &c. Imbedded in Millepora complanata, sometimes associated with Balanus Ajax.

Appearance and Structure of Shell.--Shell oval, flat, coloured pale dull purple, or white, with slight and narrow ridges, radiating, from the orifice, which is not quite central, but is placed rather nearer to the carinal than to the rostral end of the shell. The orifice is small and narrow; the carinal end being rounded, and the rostral end narrower and sharper,--this being the exact reverse of the usual shape of the orifice in the Balanidæ. The walls are thick, and are formed of large square tubes. The internal surface of the shell is smooth. The sheath (fig. 2 b) is much more elongated than the shell, for at the rostral end it extends to the basal margin, and at the carinal end nearly to it, whereas on the two sides it is some way distant from the base. The orifice is considerably out of the centre of the sheath, being placed nearest to the carinal end. The sheath has its lower edge slightly prominent or free; the lines of growth are neither turned up nor down on the two sides, as in the last three species. When nearly full grown the sheath is coloured dark purple, but when young it is white, hence the upper part is white, surrounded by an oblong purple ring, and this is surrounded by the white shell. The basal cup is deep, and internally nearly smooth. The largest specimens were .3 of an inch in their longer diameter. Great masses of the Millepora are absolutely studded with this Pyrgoma, with usually more specimens on one side of the plate or branch than on the other. They stand in approximately parallel positions, the broad or carinal ends of the orifices pointing upwards.

Scuta.--The scuta and terga are closely united, and are often (perhaps always) in some slight, though variable degree, calcified together; and hence they often break, rather than separate, at the line of articulation. The external fissure or line of junction between them (fig. 2 c) is oblique to the longer axis of the scutum; in the uppermost part of the valve it is sometimes almost obliterated. The two valves together are nearly as long as the sheath, and consequently much longer than the orifice of the shell. The scutum is much elongated, being fully four times as broad as high. The valve narrows towards the rostral end, but in a variable degree: the basal margin is hollowed out a little (but to a variable amount), close to the basi-tergal corner. Along the occludent margin a slip of the valve, widening downwards, is a little bent inwards, and this inflected portion is separated from the rest of the surface by a slightly angular ridge, running from the apex to near the rostral angle. Internally, at the basi-tergal corner, a slight ridge, parallel and close to the basal margin (and which can be seen only when the basal edge of the valve is held upwards), represents the adductor ridge, which we have seen so largely developed in the last three species, and shall again see in P. crenatum. The articular ridge (fig. 2 d) is extremely prominent, consisting of a more or less rectangular shoulder.

Terga: these are rather small compared to the scuta: they are triangular and much arched: there is no trace of a spur. Internally (fig. 2 f), the articular ridge is central: there are some vestiges of crests for the depressor muscle.

Affinities.--This well-marked species, in the tendency of the opercular valves to be soldered together, and in the remarkable absence of a trace of a spur to the tergum, is allied to P. grande, but it is more closely allied to the three following species.

7. PYRGOMA DENTATUM. Pl. 13, fig. 3 a-3 g.

Scutum much elongated, with a tooth-like articular projection: tergum convex, irregularly triangular, sometimes with an imperfect spur, and on the internal surface with an inwardly projecting tooth; scutum and tergum furnished with an occludent ledge.

Var. (1), 3 c, 3 g: tergum, with a sharp internal tooth, projecting rectangularly inwards.

Var. (2), 3 d: tergum, with a broad blunt internal tooth, depending beneath the spur-like portion of the valve.

Var. (3), 3 f: tergum, with the basi-carinal end of the valve truncated, with a small blunt internal tooth projecting rectangularly inwards.

Hab.--Red Sea; Mus. Brit. and Cuming. Also associated with Pyrgoma crenatum, and attached to Meandrina spongiosa.[120]

[120] Mr. Dana informs me that he believes that this coral comes from the West Indies; though the specimens originally described by him had no label. If this be so, both Pyrgoma dentatum and crenatum have very wide ranges.

Appearance and Structure of Shell.--Shell nearly flat, oval, white or pink, with rather distant prominent ridges radiating from the moderately large (for the genus) oval orifice. The ridges are often obscured, and apparently sometimes almost obliterated by the encrusting coral. Shell permeated near the outer lamina by short imperfect pores: internal surface smooth: sheath inconspicuous, descending rather more than half way down the walls; lower edge closely attached to the walls. Basis deep. Diameter of largest specimen .3 of an inch.

Scuta: these are elongated, but to a very variable degree, some specimens being quite three times, and some barely twice as broad as high. I observed this same variability in two sets of specimens, differing, as we shall presently see, in the form of their terga: it depends in part, but not wholly, on the varying width of the occludent ledge, which is sometimes only a fourth, and sometimes half as high as the rest of the valve. This is the first species in the genus in which the occludent ledge--a structure peculiar to the genus--has been amply developed. The basal margin of the valve is slightly sinuous, and a very little hollowed out near the basi-tergal corner; it is also very slightly reflexed, the reflexed portion being separated from the upper part of the valve by a very slight depression or even furrow. I notice this slightly reflexed portion, simply as indicating a well marked feature in the basal margin of the following closely allied species. Internally (3 g), the adductor ridge is thick and slightly prominent, but does not descend beneath the basal margin: it blends into the articular ridge, which here projects in a remarkable manner and degree (3 b, 3 e, 3 g), like a rounded tooth. This tooth is in part a development of the occludent ledge; it varies much in shape. The line of junction between the scutum and tergum is nearly straight, and nearly at right angles to their longer axes. In some specimens the scuta and terga are partially calcified together.

Terga: in three sets of specimens the terga differed considerably, but as in every other respect there was the closest resemblance, I do not doubt that these are merely varieties. In all three, the valve is rather small, irregularly sub-triangular in shape, and externally somewhat convex; in all three, there is an occludent ledge, of variable width as in the scuta; and in all three, there is an internal tooth-like projection, of variable form, unlike anything I have seen in any other cirripede. In the first variety (Pl. 13, fig. 3 c, 3 g), the basi-carinal corner of the valve is bluntly pointed, and a slight flexure separates this portion of the valve from the other and scutal half, which latter thus exhibits some tendency to be converted into a spur: on the internal surface (3 g) of this spur-like portion of the valve, there is a rather long, sharp tooth, which projects rectangularly inwards; it is flattened in a plane at right angles to the longer axis of the scutum and tergum together: it cannot be seen from the outside. In the second variety, the shape of the valve is not very different (Pl. 13, fig. 3_d_), excepting that the flexure, separating the basi-carinal corner of the valve from the spur, is deeper; but on the internal face of the spur, the tooth is far broader than in the first variety, and is flattened quite differently, viz., in a plane nearly parallel to the surface of the valve, and instead of projecting rectangularly inwards, it depends beneath the basal edge of the so-called spur, and can be seen from the outside. In the third variety (fig. 3 f), the whole carinal end of the valve is cut off, and there can hardly be said to be any trace of a spur, yet a slight furrow apparently marks the line of separation between the basi-carinal portion of the valve, here become very narrow, and the broad, irregular part, which would have formed the spur had such been developed: on the internal surface of the latter portion of the valve, there is a very small, blunt, slightly flattened tooth, projecting inwards, and more resembling that in the first than that in the second variety.

Affinities: under P. crenatum I will point out the diagnosis and relationship between this and that species.

8. PYRGOMA CRENATUM. Pl. 13, fig. 4 a, 4 b.

PYRGOMA CRENATUM. G. B. Sowerby. Genera of Recent and Fossil Shells, (No. 218, Sept. 1823), fig. 1 to 6.

Scutum much elongated, with the adductor ridge descending below the reflexed basal margin: tergum with a broad depressed spur: scutum and tergum furnished with a wide occludent ledge.

Hab.--Philippine Archipelago; Singapore; Mus. Brit., Cuming, Stutchbury; sometimes associated with Creusia spinulosa.

Appearance and Structure of Shell.--Shell not distinguishable from that of P. dentatum; nearly flat, oval, white, sometimes pale pink, with rather distant prominent ridges radiating from the moderately large oval orifice. Shell solid, or permeated near the outer lamina by short imperfect pores: internal surface smooth. The sheath descends nearly to the base of the walls; it is but little conspicuous, and its lower edge is closely attached to the inner surface of the shell. Basis deep. Diameter of largest specimen under .3 of an inch.

Scuta: in this species the scutum is more abnormal than in any other Cirripede in the whole family: this is owing both to the adductor ridge descending far beneath the basal margin, and to the great development of the occludent ledge; hence the middle and very narrow portion of the valve alone answers to the scutum, as seen in other genera. The whole valve, including the adductor ridge and the occludent ledge, is narrow, being more than twice as broad as high; but the proportional width varies, owing chiefly (as in the last species) to the varying width of the occludent ledge. This ledge commences a little way from the rostral point of the valve, and gradually widening, extends to the apex, where it is either as high or twice as high as the rest of the valve. It is articulated by a convex surface, and by a hollow on its under side with the occludent ledge of tergum. The scutum cannot be said to have any tergal margin; without, indeed, the articular surface of the occludent ledge be thus called. The basal margin is curved, and considerably reflexed, of which peculiarity we have seen a vestige in the last species: the reflexion is not well shown, owing to the foreshortening of the reflexed edge, in fig. 4 a: this reflexed edge not being shown, causes the lines of growth to appear as if they ran more transversely to the longer axis of the valve, than they really do; for they run nearly as in the scutum (fig. 3 e) of P. dentatum. The direction of these lines of growth is of importance, for they show that the elongation of the scuta is due to an inordinate increase in their breadth, as compared to the same valves in ordinary species. The adductor ridge, having a sinuous margin, runs from near the apex to near the rostral angle: it descends below the basal margin about as far as the height of the true valve, excluding the occludent ledge. Of course this adductor ridge or plate lies beneath the membrane connecting the opercular valves with the sheath, and is concealed by it, as long as these valves remain within the shell. The edge of the occludent ledge is straight, but the edge of the middle portion of the valve, that is of the true valve, is much bowed.

Terga (fig. 4 b): these are of so irregular a shape that they can hardly be described; they may, however, be said to consist of two portions joined together, of which the lower portion is a little elongated transversely, of somewhat variable shape, with part of its surface considerably depressed (compared with the rest of the valve), sometimes being even concave: this concave portion apparently answers to the spur in other cirripedes. At the scutal corner of the valve there is a shoulder (perhaps answering to the inflected scutal margin in an ordinary tergum), which locks into a hollow on the under side of the occludent ledge of the scutum. The internal surface of the so-called spur is rounded and convex. The upper part of the tergum is in main part formed by a great occludent ledge; but this, on its lower side, is bordered by a narrow irregular slip, which, as shown by the lines of growth, represents the whole of the ordinary valve, excepting, of course, the spur already described. The occludent ledges of both valves support some fine spines.

Affinities.--Observing how extraordinarily the terga varied in P. dentatum, and that the shells were identical in that and the present species, it occurred to me at first that they might, perhaps, be both extreme varieties of one form: but in the scutum of P. crenatum, the invariably great development of the adductor plate,--the marked manner in which its basal margin is reflexed,--the absence of a tooth-like articular projection,--and again in the tergum of P. crenatum, the invariably large size of the concave spur, without any internal tooth, altogether convince me that the two species must be considered as distinct. This species is allied to P. grande, in the scutum of that species having an occludent ledge, though small, and a great adductor plate. I have only further to remark, that the figure of the opercular valves, given in Sowerby's Genera of Recent and Fossil Shells, is so good, that there can not be the least doubt about the present identification.

9. PYRGOMA MONTICULARIÆ. Pl. 13, fig. 5 a-5 f.

PYRGOMA (DARACIA) MONTICULARIÆ. J. E. Gray (!). Zoological Miscellany, p. 6, 1831.

Shell of an irregular shape, with a roughened exterior border: orifice minute, circular: scutum and tergum both much elongated, calcified together without any suture, both furnished with a broad occludent ledge.

Hab.--Singapore; Mus. Brit., Cuming, and Stutchbury. Sometimes associated with Creusia spinulosa.

Appearance and Structure of Shell.--Shell dull white, very irregular in outline, sometimes rounded, more often unequally elongated, and frequently star-shaped,--the projections being quite irregular. Whole shell nearly flat, but with the central part saddle-backed, or formed into a more or less prominent ridge, extending in the line of the longitudinal axis of the animal's body: the circumferential portions of the shell not unfrequently are a little recurved upwards. Orifice extremely minute, circular. The outer lamina of shell, which is smooth, does not extend to the circumference, and consequently a rather broad, nearly equal border, which is rough, surrounds the whole shell. I have no doubt that, when the shell was alive, this border was covered by a membrane, which, in drying, has curled up and been lost, in the same manner as the strictly analogous but narrow open seam between the basal edges of the shell and the basis in some cirripedes (as in the last two species of Pyrgoma) is protected. The roughened border can sometimes be plainly seen to be formed of normal (Pl. 13, fig. 5 e) longitudinal septa having crenated edges, with shorter septa between the longer ones; but more often the septa are so irregular, and so much branched (5 d), that the whole resembles a mass of moss. Why the outer lamina of the shell in this one species does not nearly reach the circumference of the walls, I cannot conjecture. The extremely irregular, depressed shape of the shell, with the minute circular orifice, and the singular rough circumferential and often slightly reflexed border, together give to this species so peculiar an aspect, that until close examination I did not believe that it was a cirripede. The extreme irregularity of shape depends in great part upon the irregular growth of the Monticularia, in which it is imbedded.

Internally (fig. 5 b) the walls are smooth, but they are perforated by many quite irregular, small orifices, which have the appearance of having been formed by some boring animal, but really serve, as I believe, to admit threads of corium into certain irregular pores which penetrate the shell. The sheath descends but a very short distance from the orifice: it is closely attached to the walls, and might easily be overlooked. The basis is deep, of an irregular outline, like that of the shell, and is formed by a very thin shelly layer. The largest specimen which I have seen, measuring from the extreme projecting points, was .4 of an inch in diameter.

The Scuta and Terga (fig. 5 f) are calcified together without any trace of a suture; together they form a bow with the two ends curled rather abruptly inwards; they are both extremely narrow, but furnished with an occludent ledge, twice or thrice as high as the proper valves themselves. This occludent ledge, which is finely hirsute, begins at about one third of the length of the scutum from the rostral angle, and runs to near the basi-carinal angle of the tergum. The scutum itself is curved, with a slip, along the true occludent margin (best seen at the rostral end), lying in a different plane from the rest of the valve, much in the same way as in the scutum of P. milleporæ. The adductor ridge descends a very little below the basal margin of the valve, and extends for nearly its entire length: this adductor ridge makes the proper valve even narrower than it at first appears. The Tergum is extremely narrow, forming merely a border to the occludent ledge; but it is not short, being about two thirds of the length of the scutum. There is no trace of a spur; indeed, the valve is rather narrower where the spur should have stood, than it is at the basi-carinal end. The scuta and terga are calcified together by their apices.

Affinities.--Although this species, as above stated, differs so remarkably in external appearance from the other species of the genus, and, indeed, of the whole family, yet the shell in no one essential point of structure materially differs from its congeners; and if we compare the opercular valves with those of the three last species, we shall be struck with their close, yet graduated, affinity: in P. milleporæ the scuta and terga tend to become calcified together, and the rostro-occludent end of the scutum is bent into a different plane from the rest of the valve. In P. dentatum we have an occludent ledge exactly as in the present species; but in that species the adductor plate is less developed than in P. monticulariæ; on the other hand, in P. crenatum, the adductor plate is more developed than in P. monticulariæ. If in P. crenatum we were to remove the spur from the tergum (and it is much less developed in P. dentatum; and in P. milleporæ it is entirely absent) this valve would be almost identical with that of P. monticulariæ. Under these circumstances I consider it impossible to separate the present species as a distinct genus.

Species Dubiæ.

The Daracia Linnæi of J. E. Gray (Annals of Philosophy, new series, vol. 10, 1825), was published without description or figure.

The Megatrema semicostata of G. B. Sowerby, junr. (Conch. Manual, fig. 33, 1839), is not described, and is very indifferently figured without the opercular valves, and therefore can never be recognised.

There is an admirable figure of a Pyrgoma, without any specific name, in the great 'Description d'Egypte,' but from the want of some details, I cannot positively recognise the species; I am inclined to believe that it is the P. dentatum of this work.

M. Chenu, in his grand Illustrations Conchyliologiques, has given most beautiful figures of several species of Pyrgoma, and of Creusia, but unfortunately, from the opercular valves not having been figured, I find it impossible to recognise them. The new species are Pyrgoma stellata (on which I have appended a note under P. conjugatum), and P. spongiarum and P. corymbosa of Valenciennes.

6. Sub-Genus--CREUSIA. Pl. 13, 14.

CREUSIA. Leach. Journal de Physique, tom. 85, July, 1817.

Compartments four, furnished with radii; basis cup-formed: attached to corals.

Distribution, imbedded in corals throughout the tropical seas.

Creusia is closely allied to Pyrgoma; and had not this genus already been adopted by several authors, I should not, I think, myself have formed it; though, no doubt, it harmonises well with some of the other genera of the family, which are perhaps all too intimately related. Creusia differs from Pyrgoma only in the shell being separated by sutures, into four compartments, with well developed radii: in other respects, such as in general habit, in the cup-formed imbedded basis (not permeated by pores), in the opercular valves, in the characters derived from the mouth and cirri, there are no generic differences. This affinity is more particularly evident when Creusia is compared with the first few species of Pyrgoma: indeed, for a short time, I was inclined to consider var. 10 of Creusia as identical with Pyrgoma conjugatum. With respect to the species of Creusia, I confess I have been much perplexed in determining whether there be only one, or half a dozen. The latter conclusion would almost certainly be arrived at if only a few specimens were examined; and it might naturally be thought that some of the species were extremely well marked; the difficulty of drawing any line between varieties and species, begins only when some hundreds of specimens, from various parts of the world, are disarticulated, cleaned, and carefully examined. Creusia, in this respect, offers a striking contrast with Pyrgoma, in which nearly all the species are strongly characterised. The shell differs very little in the several varieties or species of Creusia; and the most marked difference, namely, whether the walls are permeated by irregular pores or not, seems certainly quite variable. It is in the opercular valves, which in other genera offer by far the most reliable character, that we encounter the chief cause of perplexity; for the characters thus derived, though at first appearing very distinct, blend into each other, and are not accompanied by any well marked differences in the shell. Only a few of my specimens have any habitat; but the geographical range, as far as it does go, throws no light on the question which forms to regard as species and which as varieties. As is generally the case with cirripedes, the variations are local, so that the greater number of specimens imbedded in the same coral resemble each other. Under these circumstances I have thought it best, after repeated examinations of a very large suite of specimens, to describe separately each variety, without attaching any name to it; but I will first make a few general remarks on the structure of the shell. If I do not thus throw much light on the subject, I shall at least not burden it with error. I believe that the species will be definitely made out only by persons resident in the coral-bearing zones. I have given copious illustrations of the opercular valves; for, if my view be correct, this genus offers a curious and striking case of variation; if, on the other hand, I am wrong, the drawings, I hope, will aid others in coming to a more correct conclusion.

1. CREUSIA SPINULOSA. Pl. 13, fig. 6 a-6 h: Pl. 14, 6 i-6 u, 6 U.

CREUSIA SPINULOSA. Leach (!). Encyclop. Brit. Suppl., vol. 3, Pl. 57, 1824.

CREUSIA SPINULEUSE. De Blainville. Dict. Sc. Nat., Pl. 116, fig. 6.

CREUSIA GREGARIA. G. B. Sowerby (!). Genera of Recent and Fossil Shells, No. 18, Sept. 1823.

---- GRANDIS. Chenu. Illust. Conch. Tab. 1, fig. 2, sed non fig. 2 a and b.

Hab.--Philippine Archipelago, China, Singapore, Java, Red Sea, West Indies; imbedded in various corals; Mus. Brit., Cuming, Stutchbury, Dunker, &c.

General Appearance.--The shell is oval, generally flat, sometimes conical, with narrow and approximate ridges radiating from the orifice (fig. 6 a). The ridges, however, are sometimes distant from each other, and considerably prominent, projecting round the basal border. The orifice is either neatly diamond-shaped or oval. The four compartments are quite distinct; the radii are generally white, of considerable width, and with their summits not oblique. The colour is either white, or pale pinkish-purple; but in var. 11, bright pink. Even in the white specimens, when well preserved, the sheath is generally, but not always, either pale or dark purple. The largest specimen which I have seen, from the West Indies, was above half an inch in diameter; but from .3 to .4 of an inch is the more usual full size. I believe that the size, as well as the great variability of the present species, is partly determined by the rate of growth of the various zoophytes in which the specimens are imbedded, for the shell has to keep on nearly a level with the surface of the coral.

Structure of Shell and Basis.--The walls are internally ribbed; the ribs being usually prominent, sometimes to such a degree as to deserve to be called plates. The outer lamina is of variable thickness, and the prominence of the internal ribs appears in considerable part to depend on the extent to which the outer lamina has been thickened from within. In many specimens, instead of the interspaces between these internal ribs or longitudinal septa being solidly filled up, separate and successive laminæ have been deposited, by which the shell is rendered cancellated or porose; but the pores are very irregular; and sometimes they form two or three irregular rows one behind the other: this structure seems eminently variable. The edges of the radii are formed by crenated, and occasionally branched, septa. That part of the alæ, which is added during the diametric growth of the shell, is very thin. The lower edge of the sheath seems always to be free. The shelly layer, forming the basis, which is deeply cup-formed, is thin, more or less finely furrowed in radiating lines, and not permeated by pores.

The opercular valves will be best described under the following eleven varieties.

Var. (1), Pl. 13, fig. 6 a, 6 b, 6 c, 6 d.--Hab. Java, and probably several other districts.--I will first describe a typical sub-variety, by which I mean a sub-variety not presenting any extreme character. The scutum is of a sub-triangular shape, with the basi-tergal corner much rounded off (6 d), and generally but not always hollowed out in a rather remarkable manner. The adductor ridge is considerably prominent, and extends high up, parallel to the articular ridge, which latter is rounded and prominent, but to a variable degree. Near the rostral angle there is sometimes a small tooth, or only a trace of one, depending beneath the basal margin; this tooth we shall hereafter see much more developed. The Tergum is about two thirds of the width of the scutum. It is often slightly beaked, but this is more conspicuous in some of the following varieties. The spur is about half the width of the valve, and its basal end is truncated, and nearly parallel to the basal margin of the valve, but the truncated form passes insensibly into a rounded outline. The shell in this variety is generally thick and is not permeated by pores; the orifice is diamond-shaped. But in another sub-variety the walls of the shell are always, or nearly always, permeated by pores, and the tergum is very much narrower, with the spur sharper, so that at first I concluded that these two sub-varieties were specifically distinct: we shall, however, soon see in var. 2 and in var. 4, that no confidence whatever can be placed in the exact breadth of the tergum, or in the porosity of the walls; hence I have been driven to consider the two varieties just mentioned as merely sub-varieties.

Var. (2), fig. 6 e, 6 f, 6 g.--Hab. China; Red Sea.--The shell is almost invariably permeated by pores, sometimes arranged in two or three very irregular rows. In some specimens the scutum exactly resembles that in var. 1, but with the tooth near the rostral angle often rather larger: in other specimens the scutum is much more elongated transversely (fig. 6 e), with the adductor ridge more medial, and the basal margin not at all hollowed out at the basi-tergal corner of the valve. The tergum, here, is the remarkable feature, being sometimes excessively narrow, with a long sharp spur, which often, but not always, terminates in a needle-like point. In other specimens, from the same coral and certainly belonging to this same variety, the valve is not so narrow (6 g), and the spur not so pointed; consequently (as in several analogous cases in other cirripedes) it is impossible to draw any line of distinction between the specimens with the narrow and broad terga.

Var. (3), fig. 6 h [Creusia gregaria of G. B. Sowerby!]--Hab. Unknown.--The scutum presents here exactly the same considerable range of variation as in var. 2. The tergum is broad, as in var. 1, but the spur is rounded, and from not being placed so immediately close to the basi-scutal angle of the valve, gives to it a rather different aspect. The breadth of the spur varies; an extreme variety is given in fig. 6 h.

Var. (4), Pl. 14, fig. 6 i, 6 k, 6 l.--Hab. Philippine Archipelago; West Indies.--The scutum here presents the same sub-varieties as heretofore, excepting that I have not seen any so much elongated transversely. The shell is covered either with slight, closely approximate ribs, as in the foregoing varieties, or with more distant and more prominent ribs. In specimens taken out of the same branch of coral the walls were either porose or solid. Sometimes the sheath is bright purplish-pink. It is the tergum, again, which presents a remarkable range of difference; for the longitudinal depression or furrow which in the former varieties was quite open, here has its edges more or less folded inwards, and is sometimes quite closed. This same variation has been commonly observed in many species of Balanus, in which it appears to be dependent on the age of the individual; but this does not appear to be the case in the present genus. As a consequence of the greater or less folding in of the two sides of the furrow, the spur is rendered more or less narrow and pointed, and thus becomes removed to a greater or less distance from the basi-scutal angle of the valve. Further, as a consequence of this folding in, the internal surface of the valve along the line of the external furrow, is raised into a longitudinal ridge. The length of the spur varies considerably. In some very young individuals, the basal margin descends lower on the scutal than on the carinal side of the spur. In one set of specimens (fig. 6 l), a plate extended from the carinal margin to near the central longitudinal ridge just mentioned: a similar structure was described under Pyrgoma cancellatum.

Var. (5), Pl. 14, fig. 6 m.--Hab. Unknown.--We have seen in vars. 2 and 3 that the scutum varies considerably in shape: here it is unusually narrow, with the adductor ridge almost touching the articular ridge. There is no little tooth near the rostral angle, and the basi-scutal corner is not hollowed out. The tergum also varies; in some individuals it is truncated and like that figured of var. 1, but rather more rounded; in other specimens (from the same branch of coral) the basal margin so blends into the spur that the latter can hardly be discriminated (fig. 6 m); in other respects the outline resembles pretty closely that of one of the sub-vars. (fig. 6 f) of var. 2. The shell is not porose; it is thick, with strong internal ribs, and resembles that of var. 1; but it is of a pale purplish colour.

Var. (6), an. spec.? fig. 6 n-6 q.--Hab. Philippine Archipelago.--This is a very remarkable variety; we have, imbedded in the same coral, and with shells absolutely identical, specimens with the scutum having three distinct but graduated forms. Firstly, a scutum transversely elongated, in all external respects like some of the varieties mentioned under vars. 2 and 3, with no rostral tooth, and not hollowed out at the basi-tergal corner, but with the adductor ridge more prominent. Secondly, a scutum of the same general shape, but with the adductor ridge so much developed (fig. 6 n) as to descend slightly beneath the basal margin, and to be seen when the valve is viewed externally; there is a very slight tooth near the rostral angle (as in some former sub-varieties), and which can be here rather more clearly seen than hitherto, to be formed by the adductor ridge (closely united to the external surface of the valve) extending thus far, and being here produced a little downwards. Thirdly (6 p), we have the adductor ridge immensely developed, descending far below the basal margin of the ordinary valve; and the basal margin at the basi-tergal corner is angularly and deeply hollowed out. The appearance of the valve is widely different from that in the first sub-variety, yet it is impossible to separate the first and second sub-varieties, and it is almost equally certain that the third sub-variety is only an exaggeration of the second. The lower edge of the adductor ridge, in the third sub-variety, varies a little in outline; it is deeply sinuous, and is produced at the rostral angle into a point, of which we have heretofore seen only a feeble representation. It would appear as if the great development of the adductor plate had caused the exterior ordinary surface of the valve to shrink or be less developed. There is a striking resemblance in the structure here described with that in Pyrgoma cancellatum and conjugatum. The terga belonging to the above scuta, also, vary; the spur being sometimes square (6 o), and sometimes bluntly pointed: when the spur runs in the same exact line (6 q) with the scutal margin of the valve, a peculiar aspect is given to it, but this is by no means always the case. Both opercular valves are often partially coloured pinkish-purple. The shell is not porose; it is thin, with remarkably prominent internal plates; it is apparently always of small size, which I attribute to this variety inhabiting a hard thin plate-like coral. The sheath is bright pinkish-purple, of which we have had instances in some of the other varieties; and the shell itself is sometimes pinkish. Taking the scutum of the first sub-variety, together with the commonest accompanying variety of tergum, I find it quite impossible to assign to it a specific character; if, on the other hand, we consider the scutum of the third sub-variety by itself, nothing can appear more distinct; but I must repeat, there can be hardly a shadow of doubt that the three sub-varieties of scutum here described, graduate into each other, and are specifically identical.

Var. (7), fig. 6 r.--Hab. Probably Philippine Archipelago, associated with Balanus quadrivittatus.--There can be hardly any question of this being specifically identical with the last variety. It inhabits a different coral. All the specimens were of small size. The walls are not so thin, and the internal ribs not so prominent as in var. 6. The sheath is either white or dull purple; I can, in short, point out no difference in the shell from the typical var. 1. The scutum is not so much elongated transversely as in var. 6, and the basi-tergal corner is more cut off,--in which respect it resembles the common varieties. The adductor ridge is largely developed, so as to be just visible when the valve is viewed from the outside, in a degree between the first and second sub-varieties of var. 6: but the most singular character is the larger development of the tooth near the rostral angle, and this was the case in the same degree in all the specimens which I examined. The tergum resembles that rather unusual sub-variety of var. 6 (fig. 6 q), which has the scutal margin and the one side of the spur forming a straight line. It appears to me that it would be absurd to consider these slight differences, in parts unquestionably subject to much variation, as specific, when we are almost forced to admit that the much greater differences in the three sub-varieties of var. 6, are not of specific value.

Var. (8).--Hab. Unknown, Mus. Cuming.--I have seen only a single specimen of this, and refer to it on account of var. 11. The shell is rather steeply conical, with distant and prominent ribs; the radii are narrow; the walls are not permeated by pores; the colour is pale purple. Altogether its external appearance is very different from that of the foregoing varieties; but the scuta are identical with those of var. 1, excepting that the rostral tooth is rather larger, being nearly as large as in the last, var. 7. The tergum precisely resembles that in some specimens of var. 2. Hence this variety differs from the first two varieties only in the shade of colour, the external shape, and the greater prominence of the external radiating ribs of its shell. All these characters are variable in the several foregoing varieties, and they have been found, as yet, insufficient to discriminate species in any genus of sessile Cirripedes.

Varieties With the Scuta and Terga Calcified Together.

Var. (9), Pl. 14, fig. 6 s [C. spinulosa, of Leach (!)]--Hab. Unknown.--The shell is undistinguishable by a single character from many specimens of the first, third, and fourth varieties; it is not permeated by pores. The scutum and tergum, with the exception of the one striking difference of their being calcified together without any trace of a suture, are identical with those of var. 3, as may be seen by comparing the figures 6 h and 6 s. Hence to separate this form specifically from var. 3, we should have to rely solely on the calcification or union of the scuta and terga; but we have seen this is a point which is variable in Elminius Kingii, Pyrgoma milleporæ, and in some species of Balanus. The serial affinities, moreover, in Pyrgoma, clearly show that this is a character of no great importance. I must add that in several specimens of several of the varieties, the scuta and terga were so closely joined, that until careful examination, I was unable to detect the suture separating them; such being the case it must be quite unimportant for any functional purpose, whether or not the valves are calcified together. I feel, consequently, hardly any doubt that I have acted right in treating the present form as a mere variety.

Var. (10) an. spec.? fig. 6 t.--Hab. Unknown.--This variety bears nearly the same relation to var. 6, as the last variety did to var. 3. The shell is rather stronger than in var. 6, with the internal ribs not so prominent; and except in being tinted pale dull purple, it differs in no respect from the shell of var. 1. If we imagine the scutum and tergum in the third sub-variety of var. 6 (6 p, 6 q), in which the adductor ridge descends far beneath the true basal margin of the valve, to be calcified together, without any suture, we shall produce almost the identical valves of the present variety. The scutum, however, here is not quite so much elongated transversely, and the occludent margin is spinose and is furnished with large teeth; these two characters give the valve a somewhat different aspect, and hence I am more doubtful than in the foregoing case, whether this form may not be specifically distinct. I must, however, state that in Tetraclita porosa, I ascertained that the teeth on the occludent margin of the scuta were even more variable than here is supposed to be the case; and as for the shape of the valve we have seen what wonderful variation there is in var. 6. The tergum in this variety is about intermediate between the two common forms, in the sub-varieties of var. 6. As for the calcification of the two valves together, we have seen, under the last variety, how little important a character it is.

Var. (11) fig. 6 U, 6 u [Creusia grandis, of Chenu, Tab. 1, fig. 2, but not fig. 2 a and b].--Hab. Singapore, associated with Pyrgoma monticulariæ.--This variety is very closely related to the last. The shell, however, has a very peculiar aspect, which made me for some time think it must be specifically distinct. It is of a much brighter pink than in any of the foregoing varieties; the surface is marked with very prominent, distant ribs, and the radii are narrow, in which latter points, together with the tint (though here brighter), this variety cannot be distinguished from var. 7. The shell, however, is permeated by several rows of pores, in which respect it resembles the shell in var. 2, and some specimens of vars. 3 and 4. In the opercular valves there is a close general resemblance with those of the last var. 10; the tooth, however, near the rostral angle, is not so prominent; and in the tergum, the spur is more truncated, shorter and broader than in var. 10, and closely resembles that in var. 1 and 2. But I cannot consider any of the points here specified of much weight.

The foregoing descriptions show how singularly the affinities of the several varieties interlock in the most complicated manner. Hereafter some one may, perhaps, succeed in grouping several of these forms as species; but I am sure he ought not to attempt it without possessing a very large suite of specimens, or without the great advantage of comparing some two or three of the forms, fresh in their native site.

Species dubiæ.--Under Pyrgoma, I have stated that though Chenu, in his 'Illust. Conch.,' has given beautiful external figures of the shells, imbedded in the coral, yet from the want of details on the opercular valves and on the structure of the shell, I cannot recognise his species. So it, likewise, is with Creusia. Chenu gives the following new species; C. radiata, multistriata, decorata, and striata. The C. madreporarum, I suspect to be the Pyrgoma milleporæ of this work, as there stated. The C. grandis no doubt is the P. grande of this work, the Nobia grandis of Sowerby. The name Creusia Childreni is given by Dr. Gray, without description or figure, in the 'Annals of Philosophy,' vol. 10, new series, 1825.

7. Genus--CHELONOBIA. Pl. 14: Pl. 15, fig. 1.

CHELONOBIA. Leach. Journal de Physique, tom. 85, (1817).

CORONULA. Lamarck. Animaux sans Vertèbres, 1818.

---- Ranzani. Memoire di Storia Naturale, 1820.

---- De Blainville. Dict. des Sciences Naturelles.

ASTROLEPAS. J. E. Gray. (Klein) Annals of Philosophy, (new series), vol. 10, (1825).

Compartments extremely thick, six; but one of them, the rostrum, internally is composed of three rudimentary compartments, united together: basis membranous: scuta narrow, united to the terga by a horny articular ridge.

Distribution, throughout the tropical, and warmer temperate seas of the whole world; attached to turtles, crustacea, or smooth gasteropod molluscs.

This is a distinct and well-defined genus. Several authors have confounded it with Coronula, but this has been owing to an entire misapprehension of the structure of the shell in the two genera. In Coronula, the parietes are very thin, and are so deeply folded as to appear like rays or septa connecting the outside of the shell (the expanded ends of the folds) and the internal surface of the shell, but the open spaces between the folds are occupied by the epidermis of the Whale, and are external to the cirripede. In Chelonobia, the parietes are remarkably thick; hence the plates or septa, connecting the outer and inner lamina, are of unusual length; and the spaces between them, though of course internal with regard to the cirripede and occupied by the ovaria, have been compared to the spaces external to and between the folded walls of Coronula. There is but little special affinity between these genera; and I regret that they have come to be placed one after the other in this work: but the elongated opercular valves,--the thick and double opercular membrane,--the weak depressor muscles,--and the peculiar manner in which the scutum is articulated by the aid of a horny projection to the tergum, may indicate some real but slight affinity to Coronula; the many points of difference, however, in the structure of the shell and of the opercular valves, and especially in the cementing apparatus of the basal membrane, and in the branchiæ, all prove that the genera are very distinct. The singular structure of the rostrum, which, in fact, consists of three compartments externally blended together, and which three correspond in all essential respects to the rostrum and two rostro-lateral compartments in the Chthamalinæ, offers a very striking point of identity with that sub-family; but neither in the mouth, cirri, or other part, can I detect any other evidence of this relationship. Having so far discussed the affinities of the genus, I may add, that the three species, though decidedly distinct, are closely and nearly equally related to each other.

General Appearance.--The shell is generally depressed, and broadly oval or almost circular; in C. testudinaria and caretta, it has a massive appearance: the surface is generally smooth, or, when disintegrated, finely striated: the colour is white. The six compartments do not differ much in size: the rostrum is rather larger than the carina, and the lateral compartments, than the carino-lateral compartments. It is remarkable that in C. caretta (Pl. 14, fig. 2), even in specimens which have not grown crowded together, the compartments are almost invariably placed rather unsymmetrically, the rostrum and carina not exactly facing each other.[121] The shell, though so thick and massive, yields easily along the lines of suture. The radii are moderately wide, or narrow, or not at all developed, being represented by mere sutures: in this latter case, in C. caretta, the orifice of the shell is enlarged, in the same manner as we have seen in some species of Balanus and Tetraclita, by the gradual wearing away of the upper part of the shell. In C. testudinaria, the radii have a singular notched structure (fig. 1 a), and the whole shell a star-like appearance. The orifice is not filled up by the elongated opercular valves,--a considerable extent of opercular membrane being visible on the two sides. The largest specimen which I have seen, namely, of C. testudinaria, was nearly two and a half inches in its longer diameter.

[121] In Mr. Stutchbury's collection there is a specimen of C. testudinaria in which there are only five compartments, one of the lateral compartments having been aborted; of this I have seen no other instance in any genus.

Structure of the Parietes.--The parietes are of unequalled thickness, especially in the first two species of the genus. From the outer lamina (see Pl. 14, fig. 4, and the section in Pl. 15, fig. 1), numerous vertical plates extend inwards, alternately to a less or greater distance, some of them reaching to the inner lamina: these answer to the longitudinal parietal septa in other genera, and the elongated cavities between them (which occur in C. testudinaria and patula) answer to the parietal tubes or pores. The radiating plates or septa have their sides finely channelled, and their basal edges generally slightly sinuous and always finely toothed. The interspaces between the plates in the uppermost part of the shell are filled up solidly, and, in C. caretta, even down to near the basis: in this latter species, the plates are irregular and much broken up, so as in parts to consist of little, separate, flattened points. In C. patula, the inner lamina of the parietes (b, in fig. 4. Pl. 14) can be best made out to be distinct from the sheath (e c e in fig. 4, and c′ in the section of C. testudinaria, fig. 1, Pl. 15). The sheath in this genus descends in a very remarkable manner to the basal membrane, and has its basal edge toothed like the basal edges of the radiating septa. The inner lamina itself does not descend to the basal membrane. In C. testudinaria, the inner lamina is of great thickness; but in the section, (fig. 1) owing to its having been taken high up, the inner lamina, (b), is not distinct from the shelly matter deposited between the septa. In C. caretta, the line of separation between the inner and outer laminæ can in no part be distinguished, owing to the interspaces between the septa having been solidly filled up, close down to the basis.

Sheath.--The layer of shell surrounding the internal cavity (e c e, fig. 4, Pl. 14), and extending down to the basal membrane, I have called the sheath, owing to its being distinctly continuous with the innermost layer in the upper part of the shell, to which the opercular membrane is attached: this can be best seen by examining the alæ in the separated compartments of C. patula. The sheath is not only remarkable from thus descending to the basal membrane, but in C. testudinaria and patula from its lower edge being perforated by arched channels (under c, in fig. 4), allowing thick ribbons of corium to reach the interspaces between the radiating septa. There is one central arch or channel in the middle of the lower part of the sheath of each compartment, and one on each line of suture, the sheath being a little hollowed out on both sides of the sutures. As the rostrum, as far as its internal structure is concerned, consists of three compartments, we have altogether in the shell eight compartments and eight sutures, and consequently altogether sixteen arches through the lower part of the sheath, allowing sixteen thick ribbons of corium to penetrate the parietes, and thus likewise reach the radii. There is, however, sometimes a little variation in the number of these arched channels. The upper part of the sheath is transversely marked by zones of growth, to the lower one of which the opercular membrane is attached. The line of attachment is not low down the sheath.

Radii and Alæ.--The radii, when the compartments are disarticulated, present a remarkable structure, from appearing to consist of a distinct inner and outer portion. The radius normally consists of an inner and outer lamina, united by septa parallel to the basis; but here the inner portion is formed by a central ridge (a a, fig. 5, Pl. 14), sending off on both sides little septa, often sub-branched; it is of nearly uniform width; and there is no distinct inner lamina. The outer portion (b), which often equals or exceeds in thickness the inner portion, is, in fact, the normal outer lamina, developed to an unparalleled degree. In most Cirripedes the edge of the radius is received in a slight furrow in the opposed compartment, the lid of which furrow is narrow, and matches the outer lamina of the radius; here the lid of the recipient furrow is very broad, and resembles the outer lamina of the radius in all its characters. In order to allow of growth between the thick opposed edges of the outer lamina of the radius and the lid of the recipient furrow, the two surfaces are finely dentated (look in fig. 5, under the pits, marked b), almost like the crown of a molar tooth; thus allowing films of corium to enter. The structure here described is common, in a greater or less degree, to all three species, but is best seen in C. testudinaria. In this species, moreover, (fig. 5, b), the outer lamina, instead of being smooth and of either equal or gradually increasing thickness from top to bottom, is generally, but not always, (fig. 1 a), deeply pitted or notched in transverse lines, the outer lamina being thus rendered alternately thicker and thinner, and so formed into transverse ridges and valleys. Hence the lines of suture become toothed, the points of the teeth facing each other, and not interlocking. In the transverse section, fig. 1, Pl. 15, of the same species, taken high up across the shell, (f) is the pitted outer lamina, and (e) the inner portion of the radius. Although the radii are thus specially added to in thickness, they are not so thick as the very thick walls, and hence the lines of suture form furrows more or less deep. The alæ are of moderate thickness, and have their sutural edges crenated by fine transverse septa.

Rostrum.--I have already alluded to the peculiar compounded structure of this compartment, unlike anything we have as yet seen.[122] The thin outer lamina is quite continuous, and shows no trace of the triple nature of the compartment; as may be seen by comparing the drawing (Pl. 14, fig. 1 a) of the shell of C. testudinaria, with the transverse section (Pl. 15, fig. 1) of the same species: in this latter figure, a is the outer lamina, and B A B the three compartments of the rostrum. But when the outer lamina is worn away, as is always the case with the upper part of the walls in C. caretta (Pl. 14, fig. 2), the two fissures separating the three compartments of the compounded rostrum, are plainly exhibited on the outside of the upper part of the shell. On the internal surface, the sutures separating the three compartments are always open, except in the upper part of the sheath, above the attachment of the opercular membrane, where they are partially obliterated by a thin continuous layer of shell. That these three portions of the rostrum are in their essential nature compartments, is well shown in C. patula and testudinaria, by the sheath or inner lamina having loopholes or channels (such as before described) in the middle of each, and on each line of suture. From the number of these channels, seven altogether, (the two between the compound rostrum and lateral compartments being counted,) the sheath of the compound rostrum is reduced to mere flattened pillars between the several channels. By slight violence, the rostrum breaks into the three portions; and the sutures between them are found to be marked on both sides by sinuous, slight, calcareous ridges, those on opposite sides locking into each; these represent the septa on the edges of the radii and alæ and their recipient furrows, in the ordinary compartments. The outline of the middle compartment of the three (best seen in section Pl. 15, fig. 1, A), much resembles that of the carina; in fact, if we suppose the growth of the two alæ of the carina to have been arrested, no essential difference can be pointed out: in this rudimentary compartment, therefore, we have a rostrum, characterised as in the sub-family of the Chthamalinæ. In the two little rostro-lateral compartments, moreover, (B B), a slight swelling on the side opposite to the large existing radius, shows that if the development of these compartments had not been prevented, each, probably, would have had, exactly as in the Chthamalinæ, a radius on both sides. In the introduction to the Balanidæ, I have argued, from the structure here described and from some other facts, that in the Balaninæ the rostrum is composed of the three anterior compartments, which we see in the Chthamalinæ, indissolubly united together; hence in Chelonobia the middle one of the three partially-blended compartments is properly the rostrum, and those on the sides the rostro-lateral compartments.

[122] My attention was first called to this peculiar structure of the rostrum by Mr. Stutchbury.

Basis.--The basal membrane extends under the thick walls to the outside. I was not able to make out the whole cementing apparatus. The main trunk is remarkable from its small diameter, (f f in fig. 2, Pl. 28), and from the distance at which the cement-glands stand apart. Each gland gives rise to a pair of cement-ducts, which tend to run in parallel groups; these ducts repeatedly bifurcate, occasionally inosculate, and decrease in diameter; they debouch and allow the cement to escape at numerous points, placed at irregular distances, on the edges of each new slip of the basal membrane.

Opercular Valves.--These are elongated; they do not fill the orifice of the shell; they are attached by a strong opercular membrane a little way down the sheath. The opercular membrane is generally double, for the last-formed membrane is not immediately moulted as soon as a new one is formed, as generally happens in Balanus. Externally, the valves are marked by rather rugged, broad zones of growth. The Scuta are elongated in the line of the orifice of the sack; the occludent margin (Pl. 14, fig. 1 b) is much inflected, and generally sinuous; along this inflected portion a distinct square-edged ridge runs, which widens from the apex downwards. The depression for the adductor muscle is very deep: there are no pits or crests for the other muscles. When the scutum is thoroughly cleaned and all the membrane removed by caustic potash, the tergal margin is marked by a slight articular ridge and furrow. This articular ridge is very remarkable from supporting a prominent, flattened crest (fig. 1 b), composed of hard, yellow, horny membrane, which overlaps the inner surface of the tergum, and exactly corresponds, in shape and purpose, with the calcareous articular ridge, when best developed in other genera. Beneath the basal and generally slightly sinuous exterior margin of the valve, that is, the margin to which the opercular membrane is attached, a slight ledge depends (fig. 1 d), which narrows off towards the rostral end of the valve. I should have thought that this had been a depending adductor ridge, as in several species of Pyrgoma, had there not been a nearly similar ledge beneath the middle part of the basal margin of the tergum. The Tergum is mitre-formed, with the summit more or less truncated, and with the carinal margin generally more sloping than the scutal margin: near the carinal margin there is a slight furrow (fig. 1 d), sometimes difficult to be distinguished, with the lines of growth curving down to it on each side, and consequently with a very slight, but variable, corresponding projection on the basal margin. This furrow and slight projection, there can be hardly any doubt, represent the spur, though here placed close to the carinal instead of to the scutal margin, as in other genera. The tergum has a small articular ridge, against which the overlapping horny articular ridge of the scutum abuts. There are no crests for the tergal depressor muscles. Altogether the scuta and terga are very peculiar. A portion dissolved in acid exhibits no tubuli. On the opercular membrane there are no hairs. The rostral depressor muscles of the scuta are singularly feeble, each consisting of only one or two, or sometimes three or four, very thin ribbon-like fasciæ; the lateral depressores of the scutum are twice as strong as the rostral depressores; and the tergal depressores a little stronger than the lateral depressores. All these muscles are plainly marked with transverse striæ.

Mouth.--The labrum is not in the least bullate, which character, as well as some others that follow, I specify on account of the apparent affinity of Chelonobia to the Chthamalinæ, as indicated by its rostrum. The crest of the labrum is notched, and on each side of the notch there is a long row of teeth, which, however, are sometimes worn away. The mandibles have five main teeth; all excepting the first being laterally double. The maxillæ are not notched. The outer maxillæ are bilobed on their inner sides.

Cirri.--The four posterior pairs, in proportion to the size of the animal, are much elongated, and are remarkable from the number of their short segments. The rami of the first cirrus are a little unequal in length. The second cirrus is moderately short, with its segments rather broad and protuberant, and thickly clothed with spines. The third cirrus is of unusual length, being but little shorter than the fourth pair; its segments, however, are broad, and are thickly clothed with spines, as are the two segments of its pedicel: hence there is no real approach to that important character of the Chthamalinæ, namely, the similarity of the third with the three posterior pairs of cirri. The numerous segments of the fourth, fifth, and sixth pairs of cirri each support only two pairs of main spines; between each of these pairs there is a little tuft of fine intermediate spines; the upper of the two tufts on each segment is the longest. In a specimen of C. patula, in which there were fifteen segments in one ramus of the second cirrus, there were fifty segments in either ramus of the sixth cirrus. At the exterior bases of the pedicels of some of the anterior cirri, there are large tufts of finely plumose, delicate hairs.

Branchiæ.--These are of large size: they consist of a single fold, much plicated and sub-plicated.

Ovaria.--The ovarian tubes run into the parietes, and fill up the interspaces between the radiating septa.

Range, &c.--The three species seem to range together, over the tropical and warmer temperate seas of the whole world. C. patula and testudinaria are found in the Mediterranean, and the former at Charleston, in the United States; I have not heard of specimens from any point further north. C. testudinaria and caretta live attached to turtles; whilst C. patula always adheres to crustacea, to large and smooth gasteropod mollusca, and, I believe, sometimes to ships' bottoms. I have not heard of the discovery of any fossil species.

Attachment.--Chelonobia patula leaves no impression on the crabs and shells to which it is attached. I have seen only a few specimens of C. testudinaria attached, and the carapaces of the turtle were not at all, or scarcely at all, indented by them. The case is very different with C. caretta, in which the shell, even of young specimens, is always, as far as I have seen, imbedded to some depth, and occasionally to a very great depth in the tortoise-shell. From the extreme hardness of the tortoise-shell, when dry, the imbedment appears more wonderful even than it really is. The younger shells have the appearance of having grown from within the carapace, and then of having burst through it, almost like little volcanos. I have seen only one very young shell (1/10th of an inch in external diameter) attached, and here there was nothing to countenance an idea which at one time occurred to me, namely, that the larva perhaps fixed itself in some little crack or cavity in the carapace, and there underwent its metamorphosis. I believe that the imbedment is effected simply by the sharp, growing, basal edges of the walls of the shell indenting the surface, and finally rupturing the outer laminæ of the tortoise-shell, through that same force by which the tender radicle of a plant penetrates very hard ground. As soon as the surface was once ruptured, the shell of the Chelonobia, growing outwards and downwards, would easily, like a wedge, turn up the laminæ of the tortoise-shell; and their ragged ends would surround the Chelonobia, as is seen actually to be the case. In the genus Coronula and its allies, which are attached to Cetaceans, we shall presently see, that the epidermis immediately under the downward growing shell, and apparently in consequence of the pressure thus exerted, is thinner than in the surrounding parts. In two specimens of Chelonobia caretta, imbedded much more deeply than usual--in one of which half the basal edge of the shell had fairly cut through the carapace, and in the other was on the point of effecting this--the tortoise-shell manifestly thinned out towards the line of yielding; now this, I suppose, must be attributed either to absorption, or to the living tortoise-shell being actually stretched till rendered transparent and ready to burst or until bursted. On the latter view of the tortoise-shell having been stretched, we must further suppose that the pressure has prevented fresh layers of tortoise-shell being deposited under the old and yielding laminæ. In one of the above two specimens, the walls of the Chelonobia were deeply folded, nevertheless the laminæ of the tortoise-shell followed every curvature, showing that, though now so rigid, during the slow imbedment of the Cirripede it must have been sufficiently pliant. A shell attached, as these two specimens were, could never be removed, and, whether dead or alive, would remain for ever imbedded in the tortoise-shell. Dr. R. Ball, of Dublin, informs me, that he has seen specimens in which the shell of the cirripede not only had penetrated the carapace, but likewise the underlying bone, and had even entered some way into the body of the turtle: it is well known that the tusk of a boar or the horn of a ruminant, when curving in abnormally, will sometimes penetrate deeply into the bones of the face or head; and this, I believe, is effected, not by the fracture of the bone, but by the absorption of the point pressed on: I conceive a similar process must have taken place in the curious specimens examined by Dr. Ball.

1. CHELONOBIA TESTUDINARIA. Pl. 14, fig. 1 a-1 d, fig. 5; Pl. 15, fig. 1.

LEPAS TESTUDINARIA. Linn. Syst. Naturæ, 1767.

VERRUCA TESTUDINARIA. Ellis. Phil. Transact., vol. 50, 1758, Pl. 34, fig. 12.

BALANUS POLYTHALAMIUS. Bock. Naturforscher, Stuch. 12, 1778, fig. 9.

LEPAS TESTUDINARIA. Poli. Testacea Utriusque Siciliæ (1795) Tab. 5, fig. 9-11.

CORONULA TESTUDINARIA. Ranzani. Memoire di Storia Naturale, Decade 1, (1820).

---- ---- De Blainville. Dict. des Sciences Nat., (1824), Tab. 117, fig. 2.

CHELONOBIA SAVIGNII (?) Leach. Encyclop. Brit. Suppl., vol. 3, 1824.

ASTROLEPAS ROTUNDARIUS. J. E. Gray. Annals of Philosoph. (new series), vol. 10, 1825.

Shell conical, depressed, heavy: radii rather narrow, depressed, generally notched on both sides.

Hab.--Mediterranean; west coast of Africa; north-east coast of Australia; Low Archipelago, Pacific Ocean; west coast of Mexico, 23° N. Attached to turtles.

It is impossible to feel sure which of the three species of the genus Linnæus had in view, when describing his Lepas testudinaria; but as Spengler has well discriminated the following species under the specific name of caretta,[123] and Ranzani the third species under patula, the present name may, without question, be retained for the following species. In several respects this species is intermediate between C. caretta and patula, but it can most conveniently be described first.

[123] I am indebted to Dr. J. E. Gray for having guided me to this identification.

General Appearance.--Shell strong, globulo-conical, depressed; outline broadly oval; surface smooth, generally well preserved, but when disintegrated, upper part finely striated; colour dead white; orifice oval elongated, rather exceeding in length one third of the longer basal diameter of the shell. The radii are rather narrow, and deeply depressed; they have their summits square: their outer lamina, as explained under the genus, on both sides of each suture is in most specimens divided into teeth, the points of which face and touch each other. These teeth or notches give quite a peculiar appearance to the shell, and alone suffice to discriminate this species; they are sometimes blunt and partially obliterated, but it is rare to find a specimen in which some few teeth do not occur in some one of the six radii. I have, however, seen two or three specimens with all six radii perfectly smooth; in one of these the general shape of the shell, without the aid of any internal characters, almost sufficed to show that it belonged to the present species; but in another specimen, which had unusually narrow radii, and the whole surface of which had undergone considerable disintegration, and was consequently striated, could only be distinguished from C. caretta by internal characters. I have seen several specimens having very irregularly shaped compartments, but generally the appearance of the whole shell is highly symmetrical, like a star; and the genus was appropriately named by old Klein, Astrolepas. In some specimens, in Mr. Cuming's collection, from the Low Archipelago, in the Pacific, taken off the toe-nail of a turtle, the shape was almost cylindrical; the shell almost resembling that of Coronula diadema. The largest specimen which I have seen was 2.3 of an inch in basal diameter, but only .55 in height.

Structure of Shell and Radii.--After the full generic description, the only point to which I need allude is, that the radiating, parietal septa, as well as the descending sheath, are much thicker than in C. patula, and that their basal edges can be plainly seen by the naked eye to be dentated with numerous points. The thickness of these plates and of the sheath varies considerably. In C. caretta, I may add, the plates are broken up into many separate points, and in this species the descending sheath is not generally perforated, excepting at the sutures, by loop-holes for the entrance of ribbons of corium. The sheath and inner lamina of the parietes in C. testudinaria, taken together, fully equal one third of the entire thickness of the walls. Flattened cavities or tubes run up between the parietal septa for about two thirds of the height of the inside of the shell. With respect to the radii, I have only to add, that the thickness of the inner portion relatively to the generally notched outer lamina, varies considerably.

Opercular Valves (fig. 1 b-1 d).--These closely resemble each other in all three species, and have been almost sufficiently described under the genus. The scutum has its occludent margin always sinuous, but to a variable degree. In one specimen there was a deep little pit at the rostral end for the rostral depressor muscle. The terga vary considerably in shape, according as the basi-carinal corner is more or less truncated. The external furrow, marking the position of the rudimentary spur, varies much in distinctness, chiefly depending upon its nearness to the carinal margin of the valve.

Mouth and Cirri.--The labrum sometimes has its teeth worn away. The second pair of cirri, relatively to the others, is shorter and thicker than in the two following species.

2. CHELONOBIA CARETTA. Pl. 14, fig. 2.

LEPAS CARETTA. Spengler. Skrifter, Naturhist. Selbskabet, Bd. 1, 1790, Tab. 6, fig. 4.

BALANUS CHELYTRYPETES. Hincks (!) sine descript., Annals of Nat. Hist., vol. 5, p. 333.

CORONULA SULCATA. Chenu. Illust. Conch., Tab. 1, fig. 1.

Shell globulo-convex, extremely massive and heavy; upper part worn, sub-striated: radii either not developed or very narrow: parietes without cavities extending up between the interrupted, radiating septa.

Hab.--West coast of Africa; northern Australia; common. Attached to, and generally imbedded in, the carapaces of turtles.

General Appearance.--Shell extremely strong, massive, heavy, broadly oval, globulo-convex, though sometimes depressed; dirty white: surface in the upper part always worn and disintegrated, hence finely striated; in the lower part a little rugged, slightly folded, and occasionally, in deeply imbedded specimens, much folded or ribbed. Orifice oval, not at all angular, rather exceeding in length one third of the basal diameter of the shell. Radii either not at all developed, or very narrow; but even in the former case the six lines of suture are plain; and in the latter case the radii lie at some depth beneath the surface of the shell. It is remarkable that the compartments are hardly ever arranged symmetrically, the rostrum and carina not facing each other exactly; and this holds good in specimens attached separately, without any apparent cause for this want of symmetry. The largest specimen which I have seen was 2.1 in basal diameter; and this, which was a steeply conical individual, was 1.1 in height; and therefore nearly twice as high as an ordinary large specimen of C. testudinaria.

Structure of Shell and Radii.--The descending sheath and radiating septa are of very variable thickness, and have their basal edges finely dentated. The septa are not continuous, from the circumference to the sheath, in unbroken plates, but are irregularly divided into separate, often short portions, and even occasionally into mere points. The sheath differs from that of the other two species in having loopholes for the entrance of ribbons of corium only on the eight lines of suture, and not (with rare exceptions) in the middle of each compartment: this is evidently due to fewer filaments of corium being here sufficient to supply the less deep interspaces between the radiating septa; for in this species there are no flattened cavities or tubes running far up the shell. The inner lamina of the walls cannot be here distinguished, for a solid, flat, calcareous surface extends from the circumference, between the radiating septa, to the sheath. The sheath, had it not been from the light thrown on this part by the other species, would have certainly been mistaken for the inner lamina of the walls. The absence of the flattened cavities or tubes extending up the parietes, seems to be the least varying character; and serves to distinguish this species from those worn and massive specimens of C. testudinaria, which have narrow and not-notched radii.

In specimens in which the radii are not developed, no vestige of the outer lamina can be detected, the lateral faces of the adjoining compartments being closely pressed together; but in specimens in which the radii have been developed and have grown, the outer lamina of course is present, and is extremely thick, with the growing edge having a branched and mammilated surface, as in C. testudinaria, but with the external surface not pitted or notched as in that species. The inner portion of the radius, whether or not developed, has nearly the same appearance, consisting of rather thick transverse septa, branching from a central ridge, which is sometimes obscure.

The Alæ are remarkably little prominent, as least in those specimens in which the radii are not developed, so that Spengler seems to have thought that the structure of the shell was essentially different from that of Balanus, which certainly is by no means the case. The edges of the alæ are very thick, nearly as thick as the inner portion of the radius.

The Opercular Valves hardly present any essential difference, compared with those of the other species; but the occludent margin of the scutum is apt to be more sinuous, and its rostral end blunter and squarer. The carinal end of the tergum is also squarer than in any common variety of C. testudinaria; the external furrow or spur, near the carinal margin, is very indistinct, and even sometimes is quite absent.

Neither the mouth nor cirri present any deviations from the generic character.

3. CHELONOBIA PATULA. Pl. 14, fig. 3 a, 3 b, 4.

CORONULA PATULA. Ranzani. Memoire di Storia Naturale (1820), Tab. 3, fig. 25-28.

ASTROLEPAS LÆVIS. J. E. Gray (!). Annals of Philosophy (new series), vol. 10, 1825.

VERRUCA CANCRI AMERICANI. Ellis. Phil. Trans., vol. 50, 1758, Pl. 34, fig. 13.

Shell steeply conical, very smooth and light; orifice large, generally exceeding half the basal diameter of the shell: radii broad, smooth, only slightly depressed.

Hab.--Mediterranean; Gambia, West Africa; Charlestown; Jamaica; Honduras; Brazil; Australia. Attached to Crustacea, smooth univalve shells, and apparently to ships' bottoms.

General Appearance.--Shell white, very smooth, of little specific gravity, steeply conical, but not high; orifice broadly oval, polygonal, very large, namely, generally exceeding half the basal diameter of the shell. The summits of the compartments are usually perfectly preserved, pointed, and often a little recurved. The radii are rather broad, very smooth, with their summits slightly oblique and arched: they are seated only a little below the general level of the parietes. I have seen one specimen rather more than one and a half inch in basal diameter, but this is an unusual size; this species not growing to so large a size as the two foregoing forms.

Structure of Shell and Radii.--The walls are here thinner than in the two foregoing species; and the basal surface of a compartment rarely equals half the basal diameter of the internal cavity of the shell, measured transversely to its longer axis. The radiating septa are also much thinner, generally sinuous, and so finely dentated along their basal edges, that the teeth can be clearly perceived only by the aid of a lens. The interspaces between the septa run up to nearly the summits of the compartments, and hence the lightness of the whole shell. The inner lamina of the parietes is here not so thick (fig. 4), and is more distinct from the descending sheath than in the foregoing species. The sheath is thin, like the radiating septa; the medial loophole in each compartment, for the entrance of a filament of corium, is much wider than in C. testudinaria, for it is generally as wide as the bordering plate on either hand; and in not a few specimens, the medial loophole is so wide as hardly any longer to deserve being so called, for the descending sheath is reduced to mere flattened pillars or legs on the sides of the sutures. Although the parietes are here not nearly so thick as in the two foregoing species, yet as the radii stand but little beneath the level of the parietes, the outer lamina of the radius has a considerable thickness, and is sometimes separated from the inner portion of the radius by an interval, in the same manner as in C. testudinaria; and the growing edges of the outer lamina exhibit traces of the same mamillated structure as figured in that species.

The Opercular Valves are apt to be rather narrower and more elongated than in the foregoing species, with the occludent margin of the scutum generally, but not always, only slightly sinuous: externally the scutum is sometimes feebly striated longitudinally. In the tergum (Pl. 14, fig. 3 b) the longitudinal furrow is generally plainer, from being more distant from the carinal margin, and the rudimentary spur itself is more prominent.

The mandibles usually have five narrow teeth; but I have seen one specimen having only four teeth, and with the inferior angle truncated. The cirri present no particular character.

SECOND SECTION OF THE SUB-FAMILY OF BALANINÆ.

[Scutum and tergum (when both are present) not overlapping each other, or articulated together; basis membranous; parietes often deeply folded, with the outer lamina, towards the basis, generally imperfect; each branchia composed of two plicated folds; shell attached to living vertebrata.]

8. Genus--CORONULA. Pl. 15, 16.

CORONULA. Lamarck. Annales du Museum, tom. 1 (1802).

DIADEMA. Schumacher. Essai d'un Nouveau Syst., &c., 1817.

CETOPIRUS (SED NON CORONULA). Ranzani. Memoire di Storia Naturale (1820).

POLYLEPAS. J. E. Gray, (Klein). Annals of Philosophy, (new series), vol. 10, 1825.

Compartments six, of equal sizes: walls thin, deeply folded, with the folds forming cavities, open only on the under side of the shell: opercular valves much smaller than the orifice of the shell.

Distribution, mundane, imbedded in Cetacea.

This genus and the three following, namely, Platylepas, Tubicinella, and Xenobalanus, have very considerable claims to be separated as a sub-family, as has been proposed by Drs. Leach and Gray. Although in structure and habits they are certainly closely related together; yet only few characters can be predicated of all four in common,--some characters failing in one genus and some in another. All four, however, differ from the foregoing genera in the opercular valves not being articulated together, being simply united by tough horny membrane; but Chelonobia makes some approach in this respect. All four have the branchiæ composed of a double fold; but this can hardly be considered a character of much weight, as may be inferred from the remarks made on this subject at p. 153 of the Introduction, where the differences of these four genera from the other genera of the family are discussed at some length. Altogether I have been led to conclude, though with much hesitation, that these genera had better not be separated as the sub-family of Coronulinæ.

Our present genus, Coronula, is closely related to Platylepas, and likewise to Xenobalanus, though this latter genus is so very different in external aspect that it might easily be mistaken for a pedunculated Cirripede. Lamarck and some other authors have placed the species of Chelonobia under Coronula, but this has arisen, as explained under that genus, from a misapprehension of their structure; the folded very thin walls in Coronula having been compared with the radiating septa of the very thick walls in Chelonobia. I may further add, that Coronula has been divided into two genera by Ranzani, on palpably insufficient grounds.

General Appearance.--The three recent species of this genus have a very handsome and striking appearance. The shell is highly symmetrical, owing to the six compartments being of the same size and having exactly the same outline. The general shape is either depressed or, as expressed by the name, like a crown. The walls are longitudinally and slightly ribbed, owing, as we shall presently see, to their wonderfully folded structure; and the surface is marked by very fine longitudinal striæ, crossed by finely beaded lines of growth. Hence the walls offer a strong contrast in appearance with the six, smooth radii, of equal breadth. The symmetrically hexagonal, or rounded-hexagonal orifice of the shell is closed by a thick, nearly horizontal membrane, supporting, towards the rostral end, the small opercular valves, with a slit, having protuberant lips, in the middle, for the protrusion of the cirri. The opercular membrane is attached all round, but a short distance beneath the summit of the shell. In regard to size, I have seen a specimen of C. diadema two inches in height and two and a half in diameter.

Structure of the Shell.--The structure at first appears singularly complicated, and quite unlike that of any other Cirripede; but the whole results simply from the folding of the very thin walls, which in all essential respects are constructed like those in Balanus. In a young specimen of C. balænaris, having the orifice of the shell 2/10ths of an inch in diameter, I found the upper part of each compartment only slightly sinuous, not more so than is common in many varieties of Balanus, but more symmetrical, for each compartment had three slight furrows, making, for the whole shell, eighteen furrows. The ensuing changes during the growth of the shell will be best understood by looking at the diagrams a, b, c, in fig. 10, Pl. 15, which are supposed to represent the basal margins of the walls of a single compartment: (a) shows the simply sinuous wall of the young shell. As the shell grows, the furrows rapidly grow deeper and deeper (b), and wider and wider; at the same time, the folds or ridges between the furrows gradually become drawn out at their ends into transverse loops (c), the extremities of which ultimately become closely pressed together--the furrows being thus converted into cavities, extending from the top to the base of the compartments. This structure in the mature shell will be best understood by looking at the transverse or horizontal section (Pl. 16, fig. 7) of the rostral end of the shell of C. diadema, in which species the folding of the walls is simpler than in C. balænaris or C. reginæ: the walls (e) are represented by a double line connected by little cross lines,--(h) being one of the transverse loops at the outer end of one of the folds, and (f′) one of the cavities between the folded walls, open at the bottom of the shell, and occupied by the epidermis of the Whale. The walls of the compartments, as here represented, (A being the rostrum, C C the lateral compartments, D D the alæ of the carino-lateral compartments,) are separated from each other by the broad radii; but if the section had been taken low down near the basis, the end of the folded wall of one compartment would have been separated from that of the adjoining compartment only by the close suture: this will be understood by a glance at the entire shell, given in fig. 3, Pl. 15. The rostrum of the same species, viewed from the inside, is shown at fig. 1, Pl. 16; here it may be observed, that the basal margin (e e′ e′′) of the folded wall is extremely oblique, the outer portion having extended downwards much more than the inner portion: this obliquity is more clearly shown in the lateral view (fig. 2) of a lateral compartment, for this figure will equally well serve for a lateral view of the rostrum (fig. 1), if the ala (a′) be supposed to be removed. The section of the rostrum in fig. 7, (A), will now be intelligible in relation to the view of the rostrum given in fig. 1, if it be borne in mind that the section has been taken high up, near the letters a, b, c′′ in fig. 1.

As above stated, the folds or ridges in the young shell become more and more transversely drawn out at their ends into the transverse loops, till the latter join and touch each other. In C. balænaris the lines of junction are simple, though very close; in the other species, the ends of the transverse loops, where touching, are finely and elegantly toothed, and thus locked together. These teeth appear single when the shell is viewed either externally or internally, but when the walls along the lines of junction are forced apart, they are seen really to consist of transverse rows of minute teeth. These teeth are less distinct, forming only sinuous ridges in C. barbara (fig. 6, Pl. 15); in all cases the teeth are formed by the modification of the very minute beads, which ornament the lines of growth on the external surface of the shell. In the rostrum of C. diadema, as seen internally (fig. 1, Pl. 16), the serrated and closely-fitting lines of junction (f) between the ends of the transverse loops of the folded walls are plainly shown. It is the more or less rounded surfaces of the transverse loops which give to the external surface of the parietes its longitudinally ribbed structure: the ribs are plainest in C. diadema, fig. 3, Pl. 15. The shell, in fact, as seen externally, consists of but an extremely small portion of the external surface of the whole length of wall, being exclusively formed of the transversely looped ends of the radiating folds, together with the radii. Owing to the ends of the transverse loops being so closely pressed together, the furrows are practically converted (as already remarked) into cavities, open only on the under side of the shell, and extending from the oblique bases of the compartments up to their apices; and these are invariably filled by the black epidermis of the Whale. Owing to this circumstance, the skin of the Whale has been mistaken by some authors for parts of the Cirripede! In C. diadema, in which the summit of the shell is often a little disintegrated, the whale's skin is often there exposed, forming three black spots at the top of each compartment. It should always be remembered that these flattened and deep cavities are furrows, which homologically ought to be open in longitudinal lines along the external surface of the shell, from the top to the bottom.

As the shell increases in diameter, each of the original eighteen transverse loops, forming the exterior surface of the shell, increases in breadth; and they would have had to increase extremely, had not some of the transverse loops become, during growth, divided into two or three new transverse loops, in a manner strictly analogous with the first formation of the eighteen folds in the young shell. In Pl. 15, fig. 7, 8, 9, we see how one of the circumferential transverse loops, by the formation of a medial furrow, or rather bay, becomes developed into two transverse loops; and it is rather important to observe that three new loops might equally well have been contemporaneously formed. By the repeated formation of new circumferential loops and the consequent formation of new folds, the wall of the shell, when old, especially in C. balænaris, becomes folded in a wonderfully complicated manner, as may be seen in Pl. 15, fig. 5, which is an exact tracing of the extreme basal edge of the wall of a shell of C. balænaris; to perceive the full amount of complication, it is advisable to trace the wall of any one of the compartments, from one suture (s) to another. In this figure the sutures are purposely drawn a little open. It may be seen that the new transverse loops, and consequently the new folds of the walls, have been, in this species, mostly formed in symmetrical order, on both sides of the six sutures; this results from the transverse loops on the sutures almost always giving rise contemporaneously to three new transverse loops. In C. diadema the transverse loops on the sutures usually divide into only two new loops, one on the rostral side and one still remaining at the suture; hence the folding of the walls in this species is much less symmetrical. The number, however, of the transverse loops and the exact pattern of the folding is variable in all four species of the genus. I may further add, to show the complication of the folds, that in a shell of C. balænaris, having a basal diameter of two inches, and which had the walls as little folded as ever they are, yet I found, by careful measurement, that the entire basal edge of the wall, if stretched straight, would have extended for a length of fifty-two inches! Therefore, if the wall had not been folded, but had been simply circular, as in ordinary cirripedes, the basal diameter of the specimen would have been between sixteen and seventeen inches!

The central membranous basis is flat, but the bottom of the folded walls of the shell is concave, which is caused by the outer ends of the folded walls having grown at a greater rate than the inner ends. The concavity is deep in C. diadema; in C. balænaris it is much less so, and here the inner hood-like ends of the folded walls are rather abruptly, but in a variable degree, produced downwards, generally even slightly beneath the level of the circumference of the shell; this fact is of interest in relation to the peculiar, depending, spur-like processes in the genus Platylepas. A lateral view of a compartment in both these species, is given in Pl. 16, figs. 2 and 3; and by supposing in each case a compartment to stand opposite, at a distance which may be judged of from fig. 5, the vertical sectional outline of the whole shell will be understood: in fig. 3 of C. balænaris, however, the inner hood-like ends of the folded walls are not produced so much downwards as is usual.

In the same manner, as the outside of the shell consists of the transversely expanded ends of the folded walls, pressed closely together, so the cavity in which the animal's body is lodged, is formed by the inner and less closely joined ends of the folds, lined by the thick sheath (a, fig. 1 and 7, Pl. 16), which latter extends down very near to the basal membrane. The cavity for the body, is small compared to the whole shell; in C. diadema it is deeply cup-formed, with a small, flat, membranous bottom or basis; in C. balænaris it is wider and shallower, with a broader bottom, and with the upper edges of the walls more inflected. In both species, the thick membrane connecting the opercular valves to the shell, is attached all round near the summit of the sheath. The uppermost portion of the sheath is not marked by concentric lines, as in most of the Balanidæ, owing to the opercular membrane not being, as we shall presently see, regularly moulted. A portion of a single wall, when closely examined, is found to be formed of an outer and inner lamina, united by longitudinal septa, and is thus permeated by minute, square, longitudinal pores,--exactly as in the normal structure of Balanus. The walls are extremely thin, and are striated longitudinally, owing to the slight projection, on both the inner and outer surfaces, of the longitudinal septa; they are thicker in the part forming the external transverse loops, being here, in C. balænaris, as much as 15/1000ths of an inch in thickness; but when forming one side of the spoke-like folds, the thickness is only 6/1000ths of an inch. The inner lamina is thicker, contrary to what is usual, than the outer lamina; the sharp tips of the longitudinal septa project a little beyond either lamina, giving to the basal edge of the wall a serrated outline. It is singular that the thin outer lamina is first formed as a rim or ledge on each side of the longitudinal septa; these ledges being not closely united for some little space up the wall, as is represented in the enlarged drawing of a bit of the basal wall of C. diadema, Pl. 16, fig. 6. The open clefts thus left are, of course, covered by the so-called epidermis, for otherwise the included threads of corium would have been exposed. Each fresh period of growth, in the case of C. diadema (fig. 6) and reginæ, and to a certain extent in C. balænaris, is marked by little knobs on the longitudinal, slightly prominent, septa, and this prefigures an analogous strongly marked structure in Tubicinella. A fine thread of corium runs up each pore to the summit of the compartment; for these pores are not, as in Balanus, cut off by transverse calcareous septa, or have their upper ends solidly filled up with shelly matter. As, however, the summit of the shell in Coronula is sometimes disintegrated, the threads of corium within the pores would have been exposed, had not each thread formed for itself, as I suppose, a transverse membranous septum near the summit of the shell; at least this is the case with the larger pores of the radii. The walls, where closely pressed together in the spoke-like folds, are disunited at the extreme base, but above this they are firmly calcified together. A ribbon of corium runs along the basal edge of each spoke, and sends threads of corium up the parietal pores on each side, and its upper edge serves to deposit calcareous matter (homologous with the layers of the sheath) and thus to unite the two walls firmly together. In C. diadema, the walls of the terminal transverse loops are simply calcified together like the spoke-like portions; but in C. balænaris the opposite sides of the loops are united by septa (see the transverse section in Pl. 15, fig. 2 a), making from five to eleven longitudinal tubes within each transverse loop; these tubes being larger than the parietal pores. When a piece of the shell is dissolved in acid, no tubuli can be discovered, which may be accounted for by the thinness of the walls; nor are there any spines on any of the external membranes. The number of the pores, in the parietes of a moderately-sized specimen of C. balænaris, I calculated was at 3400, each occupied by a thread of corium springing from the eighteen branched ribbons, diverging from the corium, surrounding the base of the sack. To this number must be added between 300 and 400 larger threads of corium running up the tubes in the transverse loops; and no less than about 2300 fringes and threads occupying the pores in the six radii: thus we see that the dermal system in Coronula is wonderfully complicated.

Radii.--The radii are very wide in C. diadema. In all the species their summits are square or parallel to the basis. Their internal structure is remarkable: as the walls in this genus are extremely thin, so are the proper radii, for in fact they consist in this and all cases, as we know, of one margin of the wall modified by its lateral growth against the opposed compartment. But as the radii in Coronula are not plicated, like the walls, the shell would have been excessively weak along the six lines of suture, had not the radii been strengthened by numerous sinuous plates, springing from the inner lamina of the proper radius, and running downwards, attached to the folded wall of the compartment to which the radius belongs, and with their free edges pressed against the folded wall of the opposed compartment. These plates give out short transverse denticuli, making altogether a beautiful structure, as is best seen in Pl. 16, fig. 3, but also in fig. 2 and 4, and d in fig. 1. In the section, fig. 7, the proper radius (d) is seen to be continuous with the wall (e), and to be very thin, in fact forming but a small portion of the compound radius: it is formed of an outer and inner approximate lamina, separated by septa, which are nearly horizontal, and which consequently cannot be shown in the transverse section fig. 7. The outer lamina of the radius is imperfect, or does not reach quite to the suture, leaving the septa a little exposed (imperfectly shown in Pl. 16, fig. 3), exactly as is the case with the outer lamina of the parietes, at the basal margin of the shell. In all common Balanidæ, a ribbon of corium runs up each of the six sutures, and sends in fine threads between the septa of the radii, but here a thread of corium runs up a minute, cylindrical pore, situated on the line of junction between the radius and the wall whence it arises; and from this longitudinal thread the finer threads spring which pass between the horizontal septa of the proper radius: this cylindrical pore is rather large in C. balænaris, but excessively small in C. diadema (see a black dot (d′) in section, fig. 7), and is solidly filled up in the upper part of the shell. The plates (fig. 3) which run down from the inner lamina of the proper radius, and form the greater part of its thickness, are occupied by fringes of corium, extending up from a ribbon of corium, running along each suture, like those which run along the bases of the spoke-like folded walls. This difference in the origin of the ribbons of corium, occupying the interspaces between the plates and the pores in the proper radii, shows the essential difference between the latter and the thick inner portions of the compound radii. In C. balænaris (fig. 3), the compound radius extends from the outside of the shell to the sheath and to near the basal edges of the folded walls: in C. diadema (fig. 2), it does not extend so far inwards and downwards; and in C. reginæ (fig. 4), even still less so. It ensues from this circumstance that when, in these two latter species, a transverse section is made across the middle of the shell, a large chamber (v, fig. 7), occupied by the ovaria, is found on each line of suture (s s), separating the radii (d) and alæ (a).

The Alæ in C. diadema (section, Pl. 16, fig. 7, a′) and C. reginæ, are of remarkable thickness, nearly equal to that of the radii, and in C. balænaris, of considerable thickness; this is evidently to give strength to the shell, which is weakest along the lines of suture, notwithstanding that the radii have been specially thickened. The edge of each ala presents a miniature resemblance of the edge of the radius, namely, a central ridge sending off on both sides sinuous plates, themselves denticulated. In C. balænaris, the ala rests almost entirely on the inner surface of the compound radius; but in the other two species, in which, as already stated, the radii and alæ are separated by chambers, the ala rests on a plate (c′′ in fig. 1, 4, and 7), which extends from the top of the radius to the bottom of the sheath, narrowing downwards (c′′, fig. 1), and is a specially developed portion of the sheath for the radius to rest on. In C. diadema and reginæ, the sides of the folded walls, at the ends of the chambers (v, in section, fig. 7), are strengthened by the deposition of layers of shell in connexion with the sheath. The sheath extends close down to the basal membrane in C. balænaris, and does not project freely: in the other two species it depends freely, but does not run quite so low down. I have only further to remark, that the sutures, though very strongly united, are not calcified together; for they easily separate after the action of caustic potash.

The Basis (Pl. 28, fig. 1 a-1 c) is membranous and is formed of concentric slips: each slip has eighteen angles, corresponding with the open ends (see Pl. 16, fig. 5) of the eighteen folds of wall. A ray of membrane runs under each of these folds, being prolonged from the basal membrane; but these rays can hardly properly be called parts of the basal membrane, for they split at each period of growth along the middle, and the two halves are drawn from under the basal edges of the walls, and thus come to invest their outer surfaces. The basal membrane, and the whole cementing apparatus, which is much simpler than in Balanus, has been fully described (p. 135) in the Introduction.

Opercular Valves.--In the sessile cirripedes hitherto examined, the four opercular valves are inclined towards each other, and nearly fill up the orifice of the shell, being united to the walls by a more or less narrow circular border of membrane; this membrane being attached rather low down to the sheath. In Coronula the opercular membrane is stretched like the skin of a drum, almost horizontally across the top of the shell; it is, however, generally attached to the sheath rather lower down at the carinal than at the rostral end: hence the animal's body, as remarked by Burmeister, is attached almost horizontally; but this we shall see, under Xenobalanus and Tubicinella, cannot be considered a character of much importance. The valves are quite small compared with the opercular membrane, and certainly are of little functional importance. The scuta in C. balænaris and diadema (Pl. 15, fig. 3 b) are sub-triangular; but the under or growing surface is elongated and arched. These valves stand almost at the rostral end of the orifice, instead of on each side of it. In C. balænaris the terga are small, with the under surface oval: in C. diadema they are either quite aborted, or are represented by a barely visible plate of shell, parallel and close to the tergal margin of the scutum. The aperture leading into the sack is formed by a nearly medial slit of considerable length, furnished with irregularly protuberant, inwardly inclined lips. These lips are formed by the development of an inner fold or crest of membrane, which can be just detected in most Cirripedes: the lips include a double fold of corium, and are covered by a delicate tunic, continuous with that lining the sack, and homologically continuous with the opercular membrane. The opercular membrane is very thick, tough, and yellowish; it is, in parts, finely plicated in lines radiating from the apices of the valves: these plicæ consist of membrane in an altered condition, being harder, more horny, and of a browner yellow; the plicæ are large at the rostral end of the scuta, and projecting beyond these valves, they afford attachment to the rostral depressor muscles. Rims of similarly modified membrane (Pl. 15, fig. 2 b) connect the scuta and terga together. The rims and plicæ are occasionally moulted together with the opercular membrane. In almost all hitherto described Balanidæ, a new opercular membrane is formed at each period of exuviation, and as soon as formed, the old one is generally moulted, together with the other membranes of the body: the case is very different in Coronula, in which it is evident, from the lines of growth on the valves and sheath, that a new membrane is formed only at rather long intervals, and that it is formed in some degree extensible, so as to allow of some growth in the shell. Two or even three of these membranes are retained at the same time, one over the other; and thus, by their joint thickness, they afford protection to the included animal's body, and compensate for the smallness of the opercular valves. In a large specimen of C. balænaris, two inches in diameter, there had been formed, since its existence as a very young shell, not more than eight opercular membranes, whereas the other membranes must have been moulted within this same period at least thirty times. In a young specimen of this species, having the orifice of the shell only two tenths of an inch in diameter, I found the opercular membrane, as usual, double. This membrane is not furnished with spines, nor is it penetrated by tubuli as in most other genera. The tissue left after the opercular valves have been dissolved in acid, presents no tubuli, or any other recognisable character, and is not divided (as is usual) into layers.

Muscles of the Sack.--These muscles differ considerably from those of other sessile cirripedes hitherto described. There are the usual five (or properly six, the two tergal muscles being here, as elsewhere, confluent) bundles of fasciæ; but they hardly can be called bundles, they are so much spread out and thin. In C. balænaris, each rostral muscle consists, in different specimens, of from three to five principal fasciæ; these, at their upper ends, are attached to the cartilaginous plicæ at the rostral extremities of the scuta; at their lower ends, they do not reach (as in all the previous genera) to the basal membrane, but after converging, they diverge again into a little fan of fibres, which are firmly attached to the corium low down on the sides of the sack. The lateral depressores of the scuta consist each of about three fasciæ, and they terminate downwards like the rostral muscles. The tergal depressores are spread out into a thin sheet; upwards they reach to the basal edges of the lips of the sack-aperture, and downwards they curve a little towards the rostral and opposite end of the shell, and extend nearly to the basal membrane. These tergal muscles include two fasciæ, larger than the others, which extend rather further, both upwards and downwards, than the other fasciæ. But the most novel character in these several muscles is that in their lower portions they do not exhibit transverse striæ, thus showing a tendency to become involuntary as in pedunculated cirripedes. This circumstance, and their feebleness, is easily accounted for by the thick unyielding nature of the opercular membrane, and the feebly developed character of the opercular valves. In C. diadema, the tergal muscles are much spread out, having, as in C. balænaris, a larger fascia on each side; but the lateral depressores of the scuta form a well defined nearly cylindrical bundle; the rostral pair are extremely weak and spread out: I could perceive only feeble transverse striæ on some of these muscles, and on others there was not the least trace of striæ. I may add that the adductor scutorum muscle is well developed, as are the eight pairs of muscles which unite the animal's body to the under surfaces of the scuta. The action of the adductor scutorum serves to close the sack-aperture, but towards the carinal end necessarily with very small force; protection in this part can only be afforded by the protuberant, valvular lips, and by the dorsal surfaces of the inwardly curled cirri, with their tufts of bristles.

Mouth.--The mouth (Pl. 26, figs. 3, 4) is much elongated transversely, and does not differ essentially from that of most other Balanidæ. The labrum is notched and not in the least bullate, though in C. diadema there is a slight prominence outside close beneath the notch. The palpi are of large size, with their bristly apices touching each other. The mandibles are very strong, with from four to five main teeth, which are remarkable by presenting only rudiments of being laterally double; but between the second and third, and between the third and fourth main teeth, there is a small intermediate tooth,--these I have not met with in any sessile cirripede hitherto described. The maxillæ are small, with the two upper spines remarkably strong. The outer maxillæ are on their inner faces bilobed. Between these organs there is a minute projection, or mentum, flattened in the longitudinal axis of the body; I have not noticed this in any previous Cirripede.

The Cirri are short and extremely much flattened: the three anterior pairs have their rami unequal in length by two or three segments; the posterior edges of their pedicels are fringed by tufts of extremely fine hairs. The pedicel of the first cirrus is very broad; its rami are short, with the segments very broad. The rami of the second and third cirri are short, with the segments protuberant in front and thickly clothed with spines; the terminal segments have some short, thick, claw-like spines. The three posterior pairs have protuberant segments, each supporting three or four pairs of short, strong, main spines, with a small intermediate tuft: the dorsal tuft is small.

The prosoma is of large size. The stomach is large, without cæca, but with some internal longitudinal plaits (in C. balænaris at least), showing a tendency to the formation of cæca. In the stomach of C. balænaris I found a considerable quantity of a conferva, too much, I think, to have got in accidentally.

Generative system.--The vesiculæ seminales are large; and at their broad blunt ends, in C. balænaris, four separate vasa deferentia enter, of which fact I have seen no other instance. The ovarian tubes do not extend up the sides of the sack, but lie at the bottom, over the basal membrane; in C. balænaris they send six short ray-like prolongations into the six sutures; in C. diadema they send similar prolongations into the sutures, and fill up, as I believe, the six chambers (Pl. 16, fig. 7, v) lying between the radii and alæ: I have examined only one specimen of C. diadema in spirits, and this had the ovarian tubes in an early state of development, when they can with difficulty be distinguished from the pulpy corium; the orange-coloured masses, however, which filled the six cavities, resembled the layer which certainly consisted of undeveloped ovarian tubes and cæca, lying over the basal membrane. The ova are wonderfully numerous; their length is 3/400ths of an inch. The larvæ have been noticed in the anatomical introduction.

Branchiæ.--These are immensely developed, covering almost four fifths of the area of each side of the sack. Each consists of two nearly equal folds, attached vertically to the carinal end of the sack, and transversely across the upper end extending to the animal's body. The outline of the free part is rounded. Both folds of both branchiæ are deeply plicated on both sides; hence the superficies of the whole is very great. We shall find that this structure is common to the three following allied genera, but with these exceptions, I have observed double branchiæ only in one species of one other genus, namely, in Chthamalus dentatus.

Attachment.--The shells adhere with remarkable strength to the whale's skin. Having, until recently, examined only separated specimens, and observing portions of the whale's skin adhering to the outside, and solidly filling up the cavities on the under side, I did not doubt that the shell had the power of forming, by its own action, a deep cavity in the skin of the whale. Inspection of the basal outline of the walls of the shell (Pl. 16, fig. 5) of C. balænaris, will show how singularly unfitted its structure is for any burrowing process; and I was led to speculate on the possibility of the pupa being able to bury itself deeply in the skin, but rejected this view as opposed to what is known of the habits and structure of the pupæ of other Cirripedes. Having now examined several specimens of C. diadema adhering, in a group, to a large piece of skin, in Mr. Stutchbury's collection, it has become evident that the attachment is as much owing to the upward growth of the whale's skin, as to the downward growth of the Coronula. In Pl. 15, fig. 4, a vertical section is given of the whale's skin, taken through the place whence a shell of C. diadema has been removed; consequently we here see nothing but the whale's skin: the upper black layer is the dark horn-coloured epidermis, forming the general surface of the whale's body, and resting on an orange-coloured fibrous layer, which is lightly shaded in the drawing. The two horns in the section are two of the eighteen projections, formed entirely of the dark epidermic layer, which fill up the eighteen flattened cavities produced by the folding of the walls. Outside the horns we see the section of a circular furrow, in which the circumferential margin of the shell was lodged; and between the horns, there is the central hollow, within which, when lined with shell, the cirripede's body was included. The circular furrow is formed in main part by the epidermic layer being thinner there than on either side, and partly by the orange-coloured, underlying fibrous layer curving a little downwards, from having apparently yielded to the pressure of the circumferential margin of the shell. With respect to the cause of the thinness of the epidermis under the circular furrow, I do not know how much to attribute to mere mechanical compression or stretching, and how much to the pressure of the shell, having checked[124] its formation. In the case of very young and small shells, it is hardly possible that their pressure can have in any way influenced the formation of new epidermic layers under the thick old layers; and we must believe, at least in these cases, that the whole effect is mechanical, the sharp basal edges of the shell having indented the epidermis; but this is not more surprising than that the radicle of a plant should penetrate hard ground. Whether the indented epidermis in the circular furrow becomes ruptured, I am not sure; ragged layers may commonly be observed outside the shell, but it is very possible that these may be the ends of layers of epidermis which have been preserved by the covering of the shell, whereas, on the surrounding parts of the whale's body, these same layers have been removed by disintegration. To return to the section,--the outline of the boss of orange-coloured fibrous tissue, under the central hollow, clearly shows that it must have been formed by its own upward growth, for it stands above the general surrounding level of the corresponding layer. This same conclusion is still more obvious with respect to the eighteen flattened prominent horns, formed of the dark epidermis; the manner in which the epidermis has been forced, moulded, and packed into the eighteen flattened and curved cavities of the shell, so as to adhere to them with considerable tenacity, is extremely curious. The prominence of these horns is so great that it appears to me quite impossible to account for them, excepting by a special formation of epidermis beneath each cavity. The basal membrane of the Coronula, which lies at the bottom of the central hollow, adheres by its own cementing apparatus; and when the larva first attaches itself, this adhesion must be very important, as it allows the basal edges of the shell, during their slow downward growth, to press firmly on the whale's skin, and so slowly indent it with the circular furrow. The final cause, probably, of the cavities on the under side of the shell in this genus, formed by the singularly convoluted parietes, is to allow of the upward growth into them of the epidermis of the whale, thus securing a firm attachment and allowing the shell to exert a strong downward pressure, and thus effect its partial imbedment, and protection from the enormous force of the waves to which it must be exposed.

[124] Formerly I was inclined to believe, as stated in my former volume on the Lepadidæ, that the cement injured the true skin of the supporting animal, but this, at least in such cases as the present, I do not now at all believe.

With respect to C. balænaris, I have seen only specimens, preserved on shrunk and twisted whale's skin, with the underlying fibrous layer not preserved; but the cavities in the shell were filled by horns of epidermis, exactly as in C. diadema. There is, however, this difference in the attachment of the two species, that in C. balænaris, owing to its depressed form, the circumference of the shell indents the whale's skin, not vertically downwards, as in C. diadema, but very obliquely outwards; and, consequently, buries itself much more completely, but less deeply, under a folded and apparently ruptured flap of the epidermis. In young specimens, of the size of a shilling, the entire shell, with the exception of the operculum, is thus covered up and protected whilst young and tender.

Geographical Distribution.--The genus is found wherever whales occur, that is, from the Arctic to the Equatorial regions, in both hemispheres. It is asserted that sometimes as many as a couple of hundred specimens will adhere to a single whale. Coronula barbara, a form closely allied to C. diadema, existed during the Red Crag period; and Bronn has described some fossil specimens from Italy.

Affinities.--In the wonderfully convoluted shell,--in the parietal tubes not being either filled up by calcareous layers or being crossed by calcareous septa,--in the outer lamina of the shell between the longitudinal septa near the basis being imperfect, Coronula differs from all the foregoing genera; in the two latter respects it agrees with the three following allied genera, viz., Platylepas, Tubicinella, and Xenobalanus. The equal size of all six compartments of the shell, has been observed in very few genera besides Coronula. In a new opercular membrane not being formed at each exuviation, and in two or three of these membranes being persistent, and in their being attached high up the sheath, this genus agrees with the three following genera alone. In the valves tending to be rudimentary, and in the protuberant lips of the sack-aperture, we have a close alliance with Xenobalanus. The muscles of the sack being spread out, and tending to lose their transversely striated character, are great peculiarities in Coronula, Tubicinella, and Xenobalanus. The simplicity of the cement-ducts is a remarkable character, observed in two of the following genera, but not in Tubicinella. The double branchiæ is a peculiarity common to all four genera. Neither the mouth nor cirri offer any new characters of much importance in Coronula or in the three allied genera: the lower teeth of the mandibles not being laterally double, but having small intermediate teeth, is the newest feature in the mouth.

1. CORONULA BALÆNARIS. Pl. 15, fig. 2, 2 b: Pl. 16, fig. 3, 5.

LEPAS BALÆNARIS. Gmelin. Systema Naturæ (1789).

---- ---- Chemnitz. Conch., vol. 8, Tab. 99, fig. 845, 846 (1785).

BALANUS ---- Bruguière. Encyclop. Method., Pl. 164, fig. 13-18 (1789).

CORONULA ---- Lamarck. Annales du Museum, vol. 1, Tab. 30, fig. 2-4 (1802).

---- ---- Chenu. Illust. Conch., Plate, fig. 1 and 4.

---- ---- De Blainville. Dict. des Scien. Nat., 1818 and 1824, Tab. 117, fig. 3, 3 a.

Shell much depressed, with longitudinal flattened ribs, having simple edges; orifice rounded-hexagonal: radii very thick, almost equalling the shell in thickness: opercular valves four.

Hab.--Attached to whales in the Southern Ocean.

Having described, under the genus, in so much detail the structure of the whole shell, it will be sufficient here to point out the characters by which this species differs from the others.

General Appearance.--The shell is generally much depressed, though sometimes, in large specimens, from the turning in of the basal edges, a considerable degree of convexity is acquired. The radii are moderately wide, and give a star-like appearance to the shell. The surface of the whole upper part of the shell is smooth; the broad and much flattened ribs (i. e. the terminal, transverse loops of the folded walls) of which each compartment is formed, generally divide at a short distance from the apex. The close sutures separating these ribs are straight, and not finely serrated, by which character alone this species can at once be discriminated from the others. The surface, when closely examined, is found to be finely striated longitudinally, and is transversely crossed, chiefly in the lower part, by minutely beaded growth-ridges. The orifice is rounded-hexagonal, and is small compared with the whole shell; it is also smaller than the basal edge of the internal cavity of the shell; consequently the whole basal edge cannot be seen through the orifice from one point of view,--the operculum of course having been removed. An unusually large specimen was 2.75 of an inch in diameter; this individual was one of the more convex varieties, and yet its entire thickness, from top to base, was only .9 of an inch.

Operculum.--Having described, under the genus, the general structure of the opercular valve, I will here only add a few details on their shape. They are small compared with the whole extent of the opercular membrane. The scuta (Pl. 15, fig. 2 b, scutum to the left) stand near each other at the rostral end of the aperture leading into the sack, with their two rostral ends united by the yellowish-brown, longitudinally plicated, horny membrane, described under the genus. The terga (fig. 2 b) stand a little apart from the scuta, on the sides of nearly the middle of the sack-aperture. The lips are protuberant and moderately developed all round. The scuta are elongated, and a little curved; including the upper imbedded portion, they are almost sub-triangular: but the under growing surface is much elongated, nearly flat, with the two ends of nearly the same width, truncated and rounded. The Tergum, in rather small specimens is, if the upper imbedded portion be included, sub-triangular, with the growing surface oval, and between one third and one half of the length of the scutum; but in large specimens, the tergum becomes style-formed, lying parallel to the tergal margin of the scutum, with the growing surface proportionally much smaller, and not above one fifth of the length of the growing surface of the scutum. Hence we see some tendency in the tergum to become rudimentary, as it is in the next species. The brown, horny, plicated substance in which the terga are imbedded, extends considerably beyond the valves themselves.

Structure of the Shell and Radii.--I have already so fully discussed this subject, that I will here only enumerate the points in which this species differs from C. diadema and reginæ:--Firstly, the more symmetrically folded walls (Pl. 16, fig. 5), new folds arising on both sides of all six sutures. Secondly, the inner ends of the folded walls, which surround the internal cavity, being almost square, but with their angles rounded; their inner ends descend some little way beneath the basal edge of the sheath, as low, or lower, than the circumference of the shell. Thirdly, the external lines of junction between the transverse terminal loops being smooth or not serrated. Fourthly, these loops being flatter towards the outside, and being internally filled by septa (Pl. 15, fig. 2 a); tubes being thus formed larger than the proper parietal pores. Sixthly, the sutural edges of the compound radii (Pl. 16, fig. 3) being very much broader in the inner and upper part of each compartment than in the outer and lower part; for in the inner and upper part they stretch from the outside of the shell to the sheath, so that the alæ rest on them, and hence no large open cavity is left between the radii and alæ; in the inner and upper part, also, the radii extend down nearly to the basal edges of the folded walls. The septa, of which the radii are formed, stand further apart than in C. diadema and reginæ. Seventhly, the alæ are only 1/5th or 1/6th of the thickness of the radii, whereas in the two other species they are very much thicker, being nearly as thick as the radii: the alæ are also here (fig. 3, a′) squarer than in those two species, that is, their basal margins are not so short compared with their upper margins; their edges present, also, a slightly different structure. Eighthly, the basal edge of the sheath does not here project freely, and does not descend quite so close to the basal membrane.

Mouth.--The palpi are furnished with a row, extending along the whole basal exterior margin, of very long upwardly pointing spines; on their upper edges there is a brush of small spines. The edge of the labrum is clothed with extremely fine spines, and is furnished with a few minute teeth. The mandibles have four teeth, and the lower end is broadly rounded and coarsely spinose: the second and third teeth are double at their points, and between the second and third, and again between the third and fourth, there is a small intermediate tooth.

Regarding the Cirri, I have nothing especial to remark.

Geographical Distribution.--I have examined nine sets of specimens, having localities attached to them: three from off New South Wales; two off the Cape of Good Hope; two from the west coast of South America; and two marked only "South Sea." Hence I am led to conclude that this species is confined to the southern hemisphere, or if it extends into the northern hemisphere, it is probably only in the Pacific Ocean. I do not believe (though so stated in some works) that this species occurs on the shores of Europe. It seems often to be associated with Tubicinella. Some specimens thus associated, sent by Mr. Bennett to Professor Owen, were said to have been attached to the Balæna australis.

2. CORONULA DIADEMA. Pl. 15, fig. 3, 3 a, 3 b; Pl. 16, fig. 1, 2, 7.

LEPAS DIADEMA. Linn. Systema Naturæ, 1767.

---- ---- Chemnitz. Conch., vol. 8, Tab. 99, figs. 843, 844.

BALANUS DIADEMA. Bruguière. Encyclop. Method., n. 164, fig. 13, 14 (1789).

CORONULA ---- De Blainville. Dict. des Sc. Nat. (1824), Tab. 117, fig. 4.

---- ---- Leach. Encyclop. Brit. Suppl., vol. iii, 1824.

---- ---- Chenu. Illust. Conch., Plate, fig. 3.

---- ---- Burmeister. Beiträge zur Naturgeschichte der Rankenfüsser, 1834, Tab. 2, fig. 1-14, 18.

Shell crown-shaped, with longitudinal convex ribs, having their edges crenated; orifice hexagonal: radii moderately thick, very broad: terga absent or rudimentary.

Hab.--Attached to whales, in the Arctic Seas; United States and Great Britain; Gulf-Stream, Atlantic Ocean; New Zealand(?).

General Appearance.--As previously remarked, owing to the fulness of the generic description, minute details on structure, excepting those characteristic of the present species, need not here be given. The crown-like shape of the shell is well expressed by its name of Diadema, but the crown tends to pass into a cylinder. The radii are extremely broad. The orifice is large, and neatly hexagonal: when the operculum is removed the whole inside of the cup-formed shell can be seen at once, for the flat membranous basis is much smaller than the orifice. The under side of the shell is deeply concave. The outside of each compartment is formed by broad, rounded, and somewhat prominent, rarely divided, ribs (i. e. the transverse ends of the folded walls); these ribs are closely united together by finely serrated lines of junction (Pl. 16, fig. 1, f). Their surfaces outside are delicately striated longitudinally, and plainly crossed (more plainly than in the foregoing and the next species) by irregular, transverse ridges, especially in the lower part of the shell. The largest specimen which I have seen was two and a half inches in diameter and two in height.

Scuta.--These are placed close together at the rostral end of the orifice, and are imbedded in the brownish, tough, longitudinally plicated, horny substance, which extends far beyond both ends of the valves. In outline (fig. 3 b) they are mitre-shaped, or rounded and sub-triangular, a little curved, and more or less elongated, being most so in young specimens; they are, however, less elongated and rather more massive than in C. balænaris. Terga,--these seem entirely absent in most specimens; but in one (fig. 3 a) I found a rudiment, namely, a short thin plate of shell, barely visible to the naked eye, extending parallel and near to the tergal margin of the scutum. The lips of the aperture of the sack are prominent, and highly so towards the carinal end.

Structure of Shell and Radii.--Owing to the shell not spreading much at the base, new folds in the walls are much seldomer formed, and therefore the external longitudinal ribs (i. e. the terminal transversely elongated loops), are much seldomer divided, than in C. balænaris or reginæ; even rather large specimens sometimes having only the original eighteen folds.[125] When new folds are formed, only one is formed on one, viz., the rostral, side of each suture, instead of on both sides, as in C. balænaris. The inner ends of the folded walls, surrounding the basal membrane, are narrow, instead of being almost square, as in C. balænaris. The lower edge of the sheath, which projects freely, descends almost to the level of the basal edges of the walls. The outer ends of the folded walls, forming the transverse loops, are internally filled up solidly by calcareous matter, instead of by septa forming tubes, as in C. balænaris. The radii (Pl. 16, fig. 2) are a little thicker in the lower and outer than in the upper and inner part of each compartment; in the middle, they do not reach the sheath by about half the thickness of the compartment, and consequently they are separated from the plates (c′′ in fig. 1 and 7) on which the alæ rest, by large chambers (v in fig. 7), which extend up to nearly the apices of the compartments: the extent, however, to which the upper ends of these chambers have been solidly filled up, varies a little. The sinuous plates forming the main portion of the compound radii are rather thinner and closer together than in C. balænaris. The alæ are thick, being thickest in the middle part, and there equal the radii in thickness; their lower margins are very short compared with their upper margins, hence they are almost wedge-formed.

[125] These should be counted on the under side of the shell, for if counted from the outside, the number would be thought to be twenty-four, as on the side of each compartment bordering the radius, a half-fold has the appearance of being a whole fold, so that in appearance six folds are added to the real number of the folds. This caution is necessary whatever the number of real folds may be, that is, whether or not the original eighteen folds have been increased by subsequent plications. These remarks, also, are applicable to the other species.

Mouth.--The teeth and fine hairs on the labrum are sometimes obscure, and sometimes plain: close outside the bottom of the medial notch, there is a small hard prominence. The palpi are broad; on their basal exterior margins there is a short row of spines, which do not equal in length the width of the palpi, and therefore are not so long as in C. balænaris. The mandibles have five main teeth, of which the second and third show only an obscure rudiment of being double; between these two teeth, and between the third and fourth tooth, there is a small intermediate tooth: the inferior angle is narrow, rounded, and spinose. The extremity of the apodeme of the maxillæ is expanded.

Cirri.--I have only to remark, that the pedicel of the first cirrus is extremely broad, and that the rami are set on in an unusually crooked manner: the basal segment of the shorter and broader ramus of this cirrus has its dorsal surface produced into a plate fringed with very fine hairs.

Geographical Distribution.--I have received only four specimens with certain localities attached to them: namely, the Arctic Seas of Scandinavia; the coast of the United States, and of Britain; and the Gulf-Stream. There is also a specimen in the British Museum, sent by Mr. Stephenson, mingled with shells of Mollusca from New Zealand; but a Coronula, procured from a floating whale in the early part of the outward voyage, might so easily be sent home with specimens subsequently collected in another county, that I do not as yet fully admit that this species is an inhabitant of the Southern Pacific Ocean: I am less willing to admit this, from suspecting that C. reginæ in the Pacific, replaces the C. diadema of our Northern Seas.

3. CORONULA REGINÆ. Pl. 15, fig. 5; Pl. 16, fig. 4.

Shell globulo-conical or depressed, with longitudinal, much flattened ribs, having their edges crenated, and their surfaces striated and granulated; orifice hexagonal: radii thin, not exceeding one fifth of the thickness of a compartment: terga absent.

Hab.--Attached to whales, Pacific Ocean; Mus. Cuming, Stutchbury, and Darwin.

I have seen eight specimens of this form--two in Mr. Cuming's collection, one of which was procured at Iquique in Peru, the other from an unknown locality; one was given me in Chile, and was stated to have come from the Pacific; two others are in Mr. Stutchbury's collection, from unknown but distinct localities, and three in a group in the British Museum. These eight specimens, of which six were collected separately, all strikingly agree in general aspect and in details of structure, so that I can easily recognise the shell, and can at once pick out a single compartment, when mingled with those of the two foregoing species; nevertheless, the differences are so small, that I at first hesitated whether to name the species; but, upon reflection, I am convinced that it is distinct. Coronula reginæ is much more closely related to C. diadema than to C. balænaris, and I suspect that it replaces in the Pacific the former of these two species.

General Appearance; shell conical, straight-sided; some specimens being nearly as much depressed as C. balænaris, and considerably more depressed than any variety of C. diadema; other specimens being globulo-conical, but rather less globular than the ordinary form of C. diadema. I may here remark, that shape is of more value in this genus, in which the shell is attached to the yielding skin of whales, than in those genera in which it adheres to rocks. The orifice is neatly hexagonal, and the whole internal cavity, when the opercular membrane is removed, can be seen from one point of view, owing to the contraction of the lower part of the cavity and small size of the basal membrane. The surface of the shell is smooth, but has, even up to the summit, a peculiar frosted appearance, different from that of the foregoing species, caused by the longitudinal striæ being rather more distinct, and being crossed by beaded, very delicate transverse lines of growth. The ends of the transverse loops, forming the exterior surfaces of the compartments, are much flattened, even more so than in C. balænaris. The lines of junction between the loops, are finely serrated, as in C. diadema; and internally they are solidly filled up, instead of being formed into a set of tubes by longitudinal septa, as in C. balænaris. The under side of the shell, with its folded walls, presents an appearance intermediate between the variable appearance of this part in the above two species.

The sutural edges of the radii (Pl. 16, fig. 4) offer by far the most remarkable character, in their thinness from top to bottom; for they hardly exceed one fifth of the thickness of the compartment, measured from the external surface to the base of the sheath; hence a very large cavity is left between the radii and alæ: in the thickness of the radii the three species already described form a series, C. reginæ at one end and C. balænaris at the other. The sinuous plates, forming the lower part of the radius, are coarser and stand rather further apart than in C. diadema. The alæ are thick, and have the same outline, being narrow at their basal margins and broad at top, as in C. diadema, with their sutural edges similarly constructed: the basal edge of the sheath likewise projects freely.

Operculum.--This resembles most closely that of C. diadema. There are no rudiments of terga. The scuta cannot be distinguished from those of C. diadema.

Mouth.--The labrum has a row of inwardly curved little teeth along the whole crest, and these I did not notice in C. diadema: there is only a trace of the prominence on the outside at the bottom of the central notch. The hairs on the basal exterior margin of the palpi are moderately long. The mandibles have five teeth. In the Cirri, the first pair resembles in its peculiar structure those of C. diadema. In the sixth pair, however, the segments support only three pairs of main spines: but the specimen was not very large, and probably in old specimens there would have been four pairs.

Summary.--The present species differs from both the foregoing only in its rather more conical and straight-sided outline, smooth, frosted surface, and in the narrowness of the sutural edges of the radii, and consequent large size of the chambers between the radii and alæ. It resembles C. diadema, as far as the shell is concerned, in the external ribs or transverse loops having their lines of junction serrated and in being solidly filled up--in the shape of the orifice and of the internal cavity of the shell--in the shape and structure of the alæ--and in the basal edge of the sheath being free. It comes nearer to C. diadema than to C. balænaris in the structure of the radii. It differs from C. diadema, and comes nearer to C. balænaris, in the external ribs being flattened, instead of being convex, and in the lines of growth being very delicate. But as it resembles C. diadema in the several foregoing characters of its shell, in the opercular valves, in all parts of the mouth (excepting the labrum), and in the cirri, it is very much more nearly related to that species than to C. balænaris.

4. CORONULA BARBARA. Pl. 15, fig. 6.

CORONULITES DIADEMA (?) Parkinson, Organic Remains (1811), vol. 3, p. 240, Pl. 16, fig. 19.

Shell (probably) crown-shaped, with longitudinal convex ribs, having their edges crenated, and their surfaces rugged, both externally and internally, with transverse ridges: radii moderately thick; the spaces between the radii and the alæ solidly filled up.

Fossil in Red Crag, (Bawdsey and Sutton); Mus. S. Wood and Geological Society.

The species here described, though near to C. diadema and easily confounded with it, I have no doubt is distinct. I owe to the kindness of the Rev. Mr. Image an examination of the original specimen figured by Parkinson; and in Mr. Stutchbury's collection there is a similar and more perfect specimen; both of these resemble C. diadema in general form, but have been too much worn to be positively identified. The following description is drawn up from some compartments collected by Mr. Searles Wood, belonging certainly to three, and probably to four individuals, one of which was young; as these specimens agree in all essential respects, I feel pretty confident that the characters, by which the present species differs from C. diadema, are of specific value.

Structure of Shell.--The longitudinal ribs on each compartment (i. e. the terminal transverse loops), are convex and prominent, as in C. diadema, but they are crossed by more prominent ridges of growth than even in the roughest varieties of that species, so that the surface of the shell is more rugged. In the three previous species, the surface of the wall entirely round the cavities occupied by the whale's skin, is striated only by longitudinal very fine lines; but here, the outer portion, or that (fig. 6) formed by each transverse loop, is crossed by transverse ridges of growth, like, but less prominent than, those on the external surface of the shell. The minute teeth, along the lines of junction between the transverse loops, are here less regular, and can hardly be said to exist; for the two edges are locked together by what may be more strictly called minute zig-zag ridges than teeth. The exact number of the circumferential plications in the walls is variable in the same manner as in the three foregoing species. The sutural edges of the radii are about as thick as, or rather thicker than, in C. diadema. As in this latter species, and in C. reginæ, each ala rests, not on the internal surface (as in C. balænaris, and in all other Balanidæ) of the radius, but on a special plate; but in C. barbara, instead of a deep chamber, running up to the apex of the compartment, being left between the radius and ala, this part is filled up almost entirely by solid shell. Although the extent to which this chamber is filled up varies a little, and although its depth varies a little in C. diadema, yet there is a marked difference between the specimens of this latter species, in which the chamber is most filled up, and those of C. barbara, in which it is least filled up. The alæ are thick, as in C. diadema, and their sutural edges have a central ridge, sending off on both sides sinuous ridges. The basal margins of the alæ are not short compared with their upper margins, and therefore the whole ala is not wedge-formed; and in this rather important respect C. barbara resembles C. balænaris (Pl. 16, fig. 3), and differs from C. diadema (fig. 2). The lower edge of the sheath does not seem to have projected freely,--in this respect, also, resembling C. balænaris. From the basal margin of the alæ not being narrow, and from the inner ends of the folded walls being, as it would appear, also broad, I have little doubt that the cavity in which the animal's body was lodged, resembled in shape that in C. balænaris, the membranous basis being larger than the orifice of the shell.

Opercular valves unknown.

Summary.--This species is more nearly related to C. diadema than to the others; but in some points, just specified, it resembles C. balænaris. The characters by which it differs from all the species are, firstly, the more prominent transverse ridges on the external surface of the shell, and more especially on the surfaces bounding the outer sides of the cavities occupied by the epidermis of the whale. Secondly, the character of the teeth, or rather ridges, along the lines of junction between the transverse loops. And, thirdly, the spaces between the radii and the plates on which the alæ rest, being solidly filled up.

Species Dubiæ.

The Coronula bifida is an Italian tertiary species, so named by Bronn, in his "Italiens Tertiär-Gebilde" (1831), p. 126. It is very possible that this may be identical with C. barbara, but Bronn does not seem to have been aware of the absolute necessity of giving minute details in his descriptions of fossil cirripedes. The chief character of C. bifida is thus given:--"Eine tiefe Furche oder Spalte theilt die Längenrippe von oben herab bis zur Hälfte, welche bei der sonst ähnlichen C. diadema entweder ganz fehlt, oder nur zuweilen kurz angedeutet ist." Had it been stated that the longitudinal ribs were divided from the middle down to the base, instead of from the top to the middle, the description would have been intelligible to me, though the character thus afforded would not have been of specific value, as this dividing of the ribs occasionally occurs in all four species, and is produced by the formation of new folds to the walls.

9. Genus--PLATYLEPAS. Pl. 17, fig. 1 a-2 b.

PLATYLEPAS. J. E. Gray. Annals of Philosophy, (new series), vol. x (1825).

CORONULA. De Blainville. Dict. des Sciences Nat. (1824).

COLUMELLINA. Bivona (fide Philippi). Nuovi generi, &c. di Molluschi, Palermo (1832).

Compartments six, each bilobed and inwardly produced, so as to form six midribs, which support the outwardly convex, membranous basis.

Distribution, throughout the tropical and warmer temperate seas. Imbedded in turtles, sea-snakes and manatee.

This small genus, consisting of three species (though I have named only two), is a very natural one, yet closely allied to Coronula. Most authors have united these genera, but in doing so they destroy two very natural little groups. Platylepas, moreover, when all its characters are considered, has as good a claim to be generically separated from Coronula, as has Tubicinella,--a genus universally admitted. I shall presently recur to this subject.

General Appearance.--The most remarkable character, and which gives a peculiar aspect to the whole shell, is that each of the six compartments has a medial fissure or fold; the shell thus consisting of twelve lobes. Each fold extends from the summit to the base of the shell, and is produced inwards in the shape of a midrib (Pl. 17, fig. 1 a). The membranous basis is supported by the basal edges of the six midribs, and is thus rendered convex. As the midrib on the rostrum would have interfered, if fully developed, with that part of the animal's thorax which I have called the prosoma, it is of less size than the other midribs; and from this same cause the whole rostrum is pushed a little on one side, generally to the left, so that the shell is not perfectly symmetrical. The midrib of the carina is less than the lateral midribs. The orifice is oval, and is more or less plainly indented by six angular points,--the worn-down summits of the six midribs. The narrow elongated opercular valves stretch from one end of the orifice to the other. The rostrum is much broader than the carina: the lateral compartments are but little broader than the carino-lateral compartments. The radii are narrow, though variable in width. The general shape of the shell varies much in the same species, being either much depressed, or rather steeply conical; either circular, or more commonly oval. The (so called) epidermis is usually persistent in the lower part of the shell. The shell itself is white. The basal diameter of the largest specimen of P. bissexlobata was nearly three-quarters of an inch.

Structure of the Parietes, Radii, &c.--The walls of the shell in P. bissexlobata are permeated by minute pores, and have exactly the same structure as in Coronula; the pores being completed by the union of ledges on the outer sides of the longitudinal septa, and the latter have little knobs formed on them at each period of growth. In P. decorata the walls are solid. Each compartment, as already stated, has a deep nearly medial furrow, the sides of which are closely pressed together, thus forming the midribs, and thus differing from the furrows in Coronula, which not being pressed together, form cavities on the under side of the shell. The inner longitudinal margin of each midrib is thickly coated by a layer of shell, and is thus rendered much more prominent than it would have been if formed exclusively by the inward folding of the wall. The upper part of each midrib forms a slight, longitudinal ridge (fig. 1 d) on the sheath, having become encased by the sheath during its downward growth. Owing to the small size of the midrib of the rostrum, there is scarcely any ridge on the sheath of this compartment. The sheath does not descend half-way down the walls in P. bissexlobata, but further down in P. decorata; but perhaps the thickened inner margins of the midribs may be considered as the downward prolongations of the sheath, and on this view the sheath descends actually to the basal membrane. The radii are narrow: their edges have simple septa, with the interspaces filled up solidly. The alæ have their sutural edges smooth.

The Basis is membranous, and more or less convex. This convexity is rendered possible by the support afforded by the basal edges of the six midribs. The so-called epidermis or membrane which covers the shell, is prolonged in six flaps under the midribs; and hence the proper basal membrane has six deep indentations, receiving the above flaps. The cementing apparatus is constructed on the same simple type as in Coronula, as has been described in the Introduction.

Scuta and Terga.--These are narrow and long, stretching the whole length of the orifice of the shell. The two valves touch each other, but are not properly articulated together: their upper surfaces scale off in layers: they resemble each other very closely in shape (fig. 1 c), being simply oblong. The membrane covering the valves supports some very minute spines, 2/1000th of an inch in length. When a portion of valve is dissolved in acid it is seen to be penetrated by very numerous tubuli. The opercular membrane is rather thick: in P. decorata I found it occasionally double; in this species it supports some very minute spines; it is attached about one third down the sheath, of which the upper part is not marked (as in Balanus) by regular concentric rings. The aperture between the valves, leading into the sack, has protuberant lips, as in Coronula and Tubicinella. The normal five bundles of muscles surrounding the sack, differently from in the two genera just mentioned, do not thin out and spread out downwards, but retaining their full thickness, reach the basal membrane, to which they are attached.

Mouth: the parts present no difference from those in Coronula; between the outer maxillæ we have the same small flattened mentum-like projection; and in the mandibles, the same small intermediate teeth between the second and third, and between the third and fourth main teeth, as in that genus. The main teeth here are more plainly double laterally. There are teeth on each side of the central notch of the labrum. The cirri differ little from those of Coronula, but the segments are not nearly so much flattened and broad, and the second and third pairs are not so short. The segments of the sixth pair support four pairs of main spines, with a few minute intermediate spines, but with no intermediate tuft.

Branchiæ: these consist on each side (at least in P. decorata) of a double fold, much less plicated than in Coronula; the fold nearest to the animal's body is rounder, and not quite so large as the outer fold.

Range and Habits.--The P. bissexlobata ranges from the Mediterranean and west coast of Africa to the West Indies, to the north-east coast of Australia, and, judging from the name given by Chenu, to California: the second species, P. decorata, inhabits the Pacific Ocean; and the third imperfectly known species, was deeply buried in the skin of a sea-snake, off Borneo. The P. bissexlobata is attached both to turtles and to the skin of the manatee: some specimens in the British Museum, attached to the latter, from the west coast of Africa, were entirely buried in the skin, with the exception of the operculum. The specimens of P. decorata, which I obtained at the Galapagos Archipelago, were buried about half their depth in the softer parts of the skin of the green turtle. I do not doubt that the imbedment is effected in the same manner as in the case of Chelonobia.

Affinities.--This genus, in general structure and habits, approaches closely to Coronula; but it differs from all the species of that genus in the following respects, which appears to me fully to justify its generic separation:--The outline is often oval, instead of circular; the compartments are not of equal sizes and shapes; each compartment has here only one inward furrow or fold, and this has its sides pressed closely together, and is encased, but not obliterated, by the sheath; the rostrum is not quite medial; and the radii are narrow and nearly solid. The opercular valves, again, are here more developed, and their microscopical structure is different. The opercular membrane is less constantly double; and, what is much more important, the muscles of the sack are not here spread out, and show no tendency to become rudimentary and lose their transverse striæ. The cirri differ only in not being so broad and flattened. The branchiæ are not quite so much developed. Finally, I may add, that in several of the above respects in which Platylepas differs from Coronula, it approaches ordinary sessile cirripedes.

1. PLATYLEPAS BISSEXLOBATA. Pl. 17, fig. 1 a-1 d.

CORONULA BISSEXLOBATA. De Blainville. Dict. des Sciences Naturelles, tom. 32, (1824), Tab. 117, fig. 1.

PLATYLEPAS PULCHRA. J. E. Gray (!). Annals of Philosophy, (new series), vol. 10, (1825).

COLUMELLINA BISSEXLOBATA. Bivona (fide Philippi). Nuovi generi di Mollusch. (1832), Tab. 3, fig. 1.[126]

CORONULA CALIFORNIENSIS. Chenu (!). Illust. Conch., Tab. 1, fig. 4.

[126] This memoir was published in the 'Effemeridi Scientifiche e Litt. per la Sicilia,' according to the 'Bibliographia Zoologiæ et Geologiæ,' by Agassiz and Strickland.

Shell with the transverse lines of growth conspicuous: parietes permeated by pores; sheath descending barely half-way down the parietes.

Hab.--Mediterranean, attached to turtles. River Gambia, attached to manatee. Honduras, attached to manatee. Moreton Bay, lat. 27° S., Australia, apparently attached to the dugong of that coast. California(?) Mus. Brit., Stutchbury, and Cuming.

General Appearance.--Shell generally much depressed, and broadly oval or circular; sometimes steeply conical. Orifice oval, generally not large. Surface rather plainly marked by closely approximate lines of growth, which with the lobed outline gives to the whole an elegantly sculptured appearance: occasionally the longitudinal ridges formed by the parietal septa are distinct. Basal diameter of largest specimen three quarters of an inch.

Structure of Shell.--I have nothing material to add to the generic description. The midribs are not so prominent as in the following species, and hence the basal membrane is less convex. The origin of the midrib as a fold is very plain. The sheath descends barely half-way down the walls, and is a little hollow on its under margin, on each side of the midrib. Beneath the sheath the parietes are finely ribbed (fig. 1 d), but to a variable degree. I may here remark, that in the specimens taken from manatee, on the coast of Africa and at Honduras, the internal ribs extended further up and were plainer, and the opercular valves seemed to be a little narrower than in the other specimens, so that I at first suspected that they were specifically distinct, but I could make out no other than these small and variable points of difference.

Scuta: oblong (fig. 1 c), about twice as long as broad, with the rostral end rounded, rather narrower than the other end, and curled a little inwards. Terga, of nearly the same shape and nearly as long as the scuta: the carinal end is rather more pointed than the scutal end of the valve, and when viewed internally, the growing surface of this end is seen to be bluntly pointed. In both valves the upper layers of shell usually scale off.

Mouth and Cirri. The only differences, compared with the following species, that I perceived, were that the hairs at the end of the palpi were here rather longer, and the fourth tooth in the mandibles rather less distinct. The rami of the first cirrus are very unequal in length.

2. PLATYLEPAS DECORATA. Pl. 17, fig. 2 a-2 b.

Shell with fine longitudinal ridges, ornamented in the lower part by minute beads; parietes not porose: basal membrane equalling in convexity the shell.

Hab.--Pacific Ocean; Galapagos Archipelago; Lord Hood's Island, Low Archipelago; Mus. Cuming, Darwin.

General Appearance and Structure.--Shell oval, with the orifice large. The walls are thick, and of less height from top to base than in the last species. The surface (and this is the chief external character) is marked by fine longitudinal ridges, each of which, when closely examined, is found to be double (fig. 2 b), and near the basis, where not abraded, to be ornamented with minute beads on each side: these beads are largest on those ridges which border the sutures. The parietes are not permeated by pores; on their inner surfaces there are a few rather prominent but short ridges, instead of the many finer ridges, as in P. bissexlobata. The sheath is of great thickness; in young specimens layers scale off its summit, all round the shell, as in Tubicinella; it is only slightly hollowed out at its lower margin; it descends more than half-way down the walls. The midribs, formed by the folded walls, are more prominent than in the last species, and descend lower down; hence the basal membrane is more convex than in the last species, for it projects downwards as much as the shell projects upwards. In medium-sized specimens, the midribs project inwards to a distance exceeding half the breadth of a compartment. A less proportional length of the midrib, in an inward direction, is formed by the inward folding of the wall, and a greater length by the thickening of its inner longitudinal margin, than in the last species. The basal edge of the inner end of the midrib is smooth.

Dimensions.--The average size of the numerous specimens which I obtained at the Galapagos Islands was about .2 of an inch in diameter, and I found none larger; but Mr. Cuming's specimens from Lord Hood's Island are half an inch in diameter.

Opercular Valves.--These closely resemble those of the former species, with the exception that the carinal end of the growing or under surface of the Tergum is much squarer.

Cirri.--The only difference which I could perceive was, that the rami of the first pair were not quite so unequal in length.

Species Dubiæ.

3. PLATYLEPAS ----?

Hab.--Imbedded in the skin of a sea-snake, taken off Borneo.

I am indebted to Dr. Gray for a single specimen of this supposed species, but as it is very young and imperfect, wanting the opercular valves and cirri, I do not choose to name it. The shell presents all the usual characters of the genus; the rostrum, I may remark, being pushed to the left side. The parietes are permeated by pores of considerable size, which shows that the species is distinct from P. decorata. On the inner basal surfaces of the walls, there are two or three very distinct ridges on each side of the midrib; and this fact, together with the size of the parietal pores, makes me suspect that it is not an immature specimen of P. bissexlobata.

10. Genus--TUBICINELLA. Pl. 17, fig. 3 a-3 c.

TUBICINELLA. Lamarck. Annales du Museum, tom. 1 (1802), Tab. 30, fig. 1.

CORONULA. De Blainville. Dict. des Sciences Naturelles, (1824).

Compartments six, of equal sizes; shell sub-cylindrical, wider at the top than at the basis, belted by several large transverse ridges.

Hab.--Southern Pacific Ocean, Western South America, New South Wales, Cape of Good Hope; imbedded in whales, and often associated with Coronula balænaris.

This genus is closely allied to Coronula, and perhaps De Blainville was right in uniting them. But Coronula, as it now stands, is so natural a genus, that it seems a pity that a form so entirely different in general aspect, as Tubicinella, should be forced into it. The main difference between these genera consists in the walls being here not folded, in the simpler radii, and in the general shape of the shell and of the included animal's body; but there are many other minor points of difference. The most novel character in Tubicinella consists in the shell being lined almost close down to the basis by the opercular membrane. In the opercular membrane thus forming a long tube, and in the general shape of the animal's body, we shall presently see that Tubicinella is closely related to Xenobalanus. In numerous other respects Tubicinella is almost equally allied to the latter genus, to Platylepas, and to Coronula. Finally, several points of structure indicate that Tubicinella may be considered as a Coronula, with the shell much simplified in structure.

1. TUBICINELLA TRACHEALIS. Pl. 17, fig. 3 a-3 c.

LEPAS TRACHEALIS. Shaw. Nat. Miscell. (1789-1813), vol. 17 (1806?) tab. 726.

---- TRACHEÆFORMIS. Wood. General Conch. (1815), tab. 4, fig. 1-3.

TUBICINELLA TRACHEALIS. J. E. Gray. Annals of Philosophy, (new series), vol. 10, (1825.)

---- MAJOR ET MINUS. Lamarck.[127] Annales du Mus. Nat., tom. 1 (1802), Tab. 30, fig. 1-2.

---- BALÆNARUM. Lamarck. Animaux sans Vertèbres, (1818).

---- ---- Chenu. Illust. Conch. (Plate).

---- ---- Sowerby. Genera of Recent and Fossil Shells (Plate).

---- LAMARCKII. Leach. Encyclop. Brit. Suppl., vol. 3 (1824), Pl. 57.

CORONULA TUBICINELLA. De Blainville. Dict. des Sciences Nat., tom. 32, Pl. 117, fig. 5 (1824).

[127] It may be observed that I have here broken through the great law of priority; for it appears to me too grossly incorrect to retain the specific name either of major or minus in a genus including a single species. Lamarck himself seems to have been of this opinion, by giving, in 1818, the new specific name of balænarum; but Shaw's name of trachealis has the clear right to priority, if major or minus be rejected.

General Appearance.--Shell elongated, sub-cylindrical, with the upper end rather wider than the lower, and therefore widening in a direction the reverse of that usual with sessile cirripedes. The shell is often a little bent to one or the other side: it is surrounded by from two or three to about ten very prominent, strong, blunt ridges or belts, placed at rather irregular distances from each other. The surface is finely striated longitudinally. The six compartments are of nearly equal sizes and shapes. In full-grown specimens the parietes are not wider at the base, and often they are even a little narrower, than at the summit of the shell: in young specimens the parietes do widen a little downwards. The radii are narrow; but in young specimens they are proportionably much broader (Pl. 17, fig. 3 b) than in old specimens. The whole compartment, including the radius and wall, is always a little wider at the summit than at the base, in accordance with the shape of the whole shell. The operculum consists of four nearly equal-sized, similar valves, projecting above the upper end of the shell, which is always broken and jagged: the valves are united to the sheath by a very thick, much folded membrane. The aperture leading into the sack is bordered by very prominent lips, projecting above the opercular valves; the latter have their upper layers always scaled off. The shell is imbedded in the whale's skin up to the level of its operculum. The largest specimen which I have seen was barely one inch (.95) in diameter at the summit, and 1.5 in length; the longest specimen which I have seen scarcely attained a length of one inch and three quarters.

Structure of the Shell.--The parietes are thin, and if the sheath (which extends to near the basis) be removed, they are rendered extremely thin. They are formed by an outer and inner lamina, united by fine longitudinal septa, projecting at the basis beyond the laminæ. The pores thus produced (which in a transverse section are oblong in outline), run up to the summit of the shell, and are not filled up by shelly matter; but I presume that the included tubular threads of corium are protected, at the broken upper end of the shell, by transverse membranous septa. The outer lamina of shell, as in Coronula, is formed, though obscurely, by the union of ledges projecting from the longitudinal septa. The circular prominent belts, surrounding the shell, are formed by the longitudinal septa, at certain, irregular and rather distant periods, growing outwards; the wall at each belt being increased to nearly twice its thickness in other parts. At each belt the threads of corium within the parietal pores lend off minute branches to supply the thickened wall. These belts, which continuously surround the shell, correspond (as is best seen in young specimens), with the little knobs or beads, which, in Coronula (Pl. 16, fig. 4), rise separately, and not quite regularly, on the longitudinal parietal septa, and which, I believe, are formed at every successive period of growth; here they are much larger, stand in straight transverse rows, become confluent, and are formed only at occasional intervals. The whole external surface of the shell is covered by membrane, stronger and more persistent than is usual with most cirripedes.

Internally the sheath extends almost to the basis of the much elongated shell, and terminates in a slight shoulder: it is divided as in common Balanidæ, and differently from in Coronula, into zones of growth, but these are very broad; at the upper end of the shell, which, as will hereafter be explained, is always breaking away, the sheath readily yields along the oblique planes, which separate the zones of growth and dip outwards: a similar but less strongly marked structure occurs in Platylepas, and in no other genus. We shall presently see that the sheath presents a much more anomalous character, in being lined down to its basal edge by the innermost and last-formed layers of the opercular membrane.

Radii.--The radii are narrow. The belts which surround the shell are prolonged, with slightly diminished prominence, across the radii, their formation being simply due to the radii being here thicker than in other parts. It can be seen more plainly in Tubicinella, than in other Balanidæ, that the membrane externally investing the shell, splits along the radii during the diametric growth of the shell, and is continually repaired and added to along these lines by new longitudinal slips of membrane. The radius consists (as usual) of an inner and outer lamina, which latter does not extend quite to the line of suture--a slightly gaping fissure being thus left. The two laminæ are connected by septa, which are not denticulated, but near the outer lamina bi- or tri-furcate, and the ends of the branches thus formed spread out, forming a sort of outer scalloped lamina, in advance of the true outer lamina. The fine threads of corium running between these septa, do not spring, as in all common cirripedes, from a fillet of corium occupying the actual suture, but from two nearly circular threads of corium occupying two tubes, which run along the line of junction between the radius and the compartment whence it springs. In Coronula alone we have a nearly similar structure; for the fine threads of corium occupying the proper radius, spring from a single very minute tube (Pl. 16, fig. 7, d′), occupying the same position with the two tubes in Tubicinella. I may further add, that the structure of the proper radius in Coronula is precisely the same as here just described, but being on so very minute a scale, I did not there describe it so carefully as I have here done.

Alæ: these are only remarkable from their extreme thinness; for they are not thicker than the inner lamina of the radius. Their sutural edges are quite smooth. Forming part of the sheath, they extend down close to the basis of the shell; where, instead of, as in general, ending abruptly in a rectangular shoulder, they slope off into their own compartment.

Basis.--The basal membrane is complicated, owing to the shell, when full-grown, barely, or not at all, increasing in diameter, and, in consequence, membrane after membrane, each with its own cement-ducts attached to it, are thrown down one nearly over the other. In the Introduction (p. 143--Pl. 28, fig. 3), I have fully described the cementing apparatus, which is very curious from one of the ducts always having a loop with two spurs projecting from it. The basal membrane does not equal in diameter the base of the shell, for the membrane externally covering the walls is inflected inwards all round for a considerable width, and is then united to the basal membrane: in Coronula, the basal membrane extends only under the internal cavity of the shell, and not under the folded walls, and therefore presents a somewhat analogous structure.

Opercular Valves.--The scuta and terga are nearly of the same size and shape: they are mitre-formed, and higher than broad. They do not fill up the orifice of the shell. The scutum is a little larger than the tergum, and rather less symmetrical, the rostral corner of the valve being a little produced. There is no hollow or crest for the adductor muscle, which is small. In the tergum there is no trace of a spur. The two valves are not articulated together, but standing close to each other are united, as well as the scutum to the scutum, and tergum to the tergum, by thick, brown, tough, yet soft membrane, in layers continuous with, but differing in appearance from, the surrounding opercular membrane. The layers of shell, forming the valves, are thick, and only the three or four lower layers are usually preserved, the upper ones having symmetrically scaled off, leaving snow-white surfaces. Owing to the thickness of the successive shelly layers, and to the circumstance of each new layer being but very little larger than the last, the scaling off of the old upper layers is a quite necessary process; for otherwise the orifice into the sack would have been encumbered and almost closed by four long, slightly tapering points, prolonged upwards from the basal layers that form the four existing valves. The same scaling off process takes place in Platylepas, and amongst pedunculated cirripedes in Lithotrya. Microscopical examination does not exhibit any fine spines on the membrane investing the valves, or any tubuli in the shelly layers after their dissolution in acid: in this respect the valves resemble those of Coronula. The summits of the valves project freely for about a third of their own height, above the level of the membrane by which they are surrounded. The orifice leading into the sack is bordered by very protuberant lips, standing up even considerably above the upper freely projecting portions of the valves.

The Opercular Membrane, connecting the valves and the top of the shell, is thick and tough, and deeply folded in concentric wrinkles. As in Coronula, it consists of two or three separate membranes (each composed of many laminæ) one over the other, united to successive shelly layers of the opercular valves. As the upper shelly layer scales off, the membrane attached to it is likewise thrown off. The innermost laminæ of the last-formed opercular membrane extend down, closely attached to the sheath, to its basal edge, and therefore nearly to the basis of the shell; the outer and older laminæ, all closely attached one within the other and to the sheath, extend to a less and less distance downwards; consequently, the animal's body is enclosed in a tube, thinning out downwards, formed by the laminæ of the successive opercular membranes, surrounded outside by the shell: only in the following genus, Xenobalanus, shall we meet with a nearly analogous structure. As the shell of Tubicinella increases in diameter, from the growth of the radii, the opercular membrane lining the sheath is necessarily split along the six lines of suture, in the same manner as is the membrane externally investing the shell; in a like manner, also, it is repaired and added to by new longitudinal slips of membrane. Of this structure, in the opercular membrane, I have seen no other instance; for in most genera the old opercular membrane is moulted, and a new and larger one formed at each period of growth; in Coronula, in which the opercular membrane is likewise for a time persistent, it does not run far down the inside of the shell, and each new membrane is formed large and extensible, so as to allow, without splitting, of some increase in the diameter of the shell. The opercular membrane at the summit of the shell, in Tubicinella, is folded in concentric lines, and so deeply, that the basal edges of the opercular valves are generally hidden: this folding arises partly from each last deposited and innermost membrane being originally formed slightly folded, but chiefly from the rapid downward growth of the shell, and the consequent downward movement of the whole animal's body, together with the opercular valves to which the body is attached, and this necessarily tends to wrinkle and fold the opercular membrane. Owing to the opercular membrane extending far down inside the shell, and being firmly attached to the sheath, as the upper part of the shell breaks away and disintegrates (which we shall presently see is constantly taking place), small particles of shell are left adherent to the circumferential and folded parts of the opercular membrane; and this at first much perplexed me.

Muscles of the Sack: these extend down almost to the base of the shell, but in the lower part they spread out and become thin and very irregular, not even corresponding on the opposite sides of the body. The fasciæ in the upper part show very distinct transverse striæ, but lower down these become either obscure or entirely deficient. In all these characters the muscles of Tubicinella and Coronula resemble each other. The rostral depressor muscles of the scuta consist each of four small bundles of fasciæ; the lateral depressores run not quite straight down, but in a curved course towards the carinal end of the sack: the tergal depressores are proportionally smaller than in ordinary sessile cirripedes, but they project and form two crests (with some fasciæ between them), which support the Branchiæ. The membrane lining the sack, I may here mention, is unusually strong.

Branchiæ.[128]--These are enormously developed; the two together covering two thirds of the area of the sack. Each consists of two folds, both deeply plicated. They are attached longitudinally to the two crests, including and formed by the muscles running from the terga to near the basis of the shell. The branchiæ are likewise attached transversely to the sack, under the basal margins of the terga.

[128] These have been described by Professor Owen in the second volume of the 'Descriptive Catalogue of the Museum of the Royal College of Surgeons.'

Mouth.--The labrum is very finely hirsute, without teeth; the palpi have a short row of moderately long spines along their exterior basal margins. The mandibles have four rather narrow, sharp teeth, which (excepting the first) have double points: between the second and third, and again between the third and fourth teeth, there is a single small intermediate tooth: the inferior angle is irregularly pectinated. The maxillæ are small; there is a small notch beneath the two upper great spines, and a second notch near the inferior angle. Between the outer maxillæ, there is a square-topped mentum. Hence we see that the mouth in all its few peculiarities, resembles that of Coronula.

Cirri.--These are short, with short and broad segments protuberant in front. The pedicel of the first cirrus is very broad, and exteriorly clothed with fine hairs: its rami are slightly unequal in length. The second and third cirri are very short. The three posterior pairs are remarkable from the pairs of main spines being placed so close one under the other, and in an oblique direction, that at first they appear to form a single crowded transverse row: the dorsal tufts are rather large.

Body.--The body is remarkable from its nearly vertical position, and from the much elongated pyramidal form of the prosoma, extending down nearly to the bottom of the sack. The membrane investing the prosoma, presents a few circular folds, falsely appearing like articulations. The œsophagus enters the stomach rather obliquely. With respect to the generative system, I have only to remark, that the vesiculæ seminales are of great length, and convoluted to a remarkable degree. The ovarian cæca, form a thick layer at the bottom of the sack; they do not appear to extend up the shell round the sack. The only other point, which I shall here mention, is that beneath the basal articulation of the first cirrus, there is a longitudinal swelling, ending in a freely projecting point, .06 of an inch in length; at first, I thought, that we here had a rudiment of a filamentary appendage like those found in several Lepadidæ; but closer examination showed an orifice at the apex, leading into the acoustic meatus, in which the singular, wrinkled, heart-shaped acoustic vesicle, mentioned in the Introduction, hangs suspended. Alongside the freely depending point, with an orifice at its end, there is a smaller upward projecting point, without any orifice, but hollow within and lined by corium; I believe it opens internally into the acoustic meatus.

Attachment and general Growth of Shell.--All the specimens which I have seen have been attached in groups. They are buried up to the level of the operculum in the whale's skin; and their summits, I suspect, lie even beneath the general surface of the body of the whale. It is certain that the shells grow much at their basal ends. As in the case of Coronula, the flat membranous basis does not actually penetrate the skin; but the general pressure of the whole group of shells seems to push inwards the skin of the whale, and directly beneath each shell the formation of new epidermis is apparently checked. Between the shells, however, though close together, the epidermis continues to be formed, and is pushed upwards between them, in the same manner as it is forced into the flattened cavities on the under side of the shell of Coronula.

The manner in which a full-grown shell assumes its ordinary shape, at first appears very perplexing:[129] it has to change from a cylinder, at first probably not much above the 1/50th of an inch in diameter, to a cylinder nearly one inch in diameter: and this is not effected by the growth of the radii, for the radii never reach the basis, and the basis of course has to increase in diameter like the rest of the cylindrical shell. The radii serve only to keep the summit of the shell wider than the basis, which is the natural shape of this species; and in large-sized specimens, this purpose is sometimes aided by the parietes during their downward growth decreasing slightly in width. In ordinary nearly full-sized specimens, the parietes are of the same width at the top and bottom, but in some large-sized specimens, as just stated, they even become narrower towards the bottom; as they grow only at the bottom, one does not at first see how they can ever increase in width, or how the older shells can have acquired their present diameter. But an examination of young specimens, from .1 to .3 of an inch in diameter, at once serves to show how the shell attains its full size and shape: for here the parietes are all found to increase downwards sensibly in width, though at a much slower ratio than in other sessile cirripedes; in larger, but not full-grown specimens, a similar increase can by care be detected: hence by long-continued growth at the base of the shell, with the removal of the upper part, a young Tubicinella of small diameter will be converted into an old one of large diameter, retaining during all the time its sub-cylindrical form, with its summit rather broader than its base. With respect to the removal of the upper part of the shell, this seems almost constantly going on, for the summit of every specimen invariably had a freshly broken aspect. The peculiar structure of the sheath, which is the strongest part of the shell, namely, its division into oblique layers, separable by a slight force, doubtless is subservient to the repeated breakage of the summit. In some species of Tetraclita and of Balanus, gradual disintegration of the upper part of the shell is a necessary element in the growth of the animal, in order that the orifice may increase in size, and here we have mechanical breakage equally necessary.

[129] I am indebted to Dr. J. E. Gray for calling my attention to this subject, and explaining to me several points.

Some curious results follow from the peculiar growth of Tubicinella just described. At Plate 17, fig. 3 b, we have a careful drawing of a lateral compartment, together with its radius, (which latter does not here concern us), taken from a shell .2 of an inch in diameter. The two protracted dotted lines show the form which this compartment would have assumed, if it had continued growing downwards at the same rate of increase in width as hitherto. But the increase in width always seems to become less and less as the shell grows older; hence the dotted lines, representing the wall after long-continued growth, ought to have been drawn diverging or widening still more slowly than they do. The lateral compartment in fig. 3 a is the exact size of the compartment of a large specimen nearly one inch in diameter; in this specimen the parietes, far from increasing in width downwards, had commenced, as is represented, decreasing. Compartments of all intermediate sizes between those figured at 3 a and 3 b can easily be shown in different specimens. From these facts we may safely infer, that if the whole growth of the compartment 3 a had been preserved, instead of its upper end having been continually chipped away, it would have had even a more tapering form than that represented by the whole and dotted lines in the two figures, and would have exceeded six inches in length! this of course being also the length of the whole shell. The young Tubicinella, of which 3 b is a compartment, was imbedded in the whale's skin nearly up to the level of its operculum; if it had lived, it would no doubt have grown to the length just specified, viz., above six inches, but as all the growth is at the lower end, the bottom of the shell, it might be thought, would necessarily have become buried in the whale's skin to this same depth; and the summit of the shell, on this same view, would have been buried to a depth by as much less as the height or length of the old shell itself, namely, by about one inch and a half less than the six inches. As far as I can judge from an examination of several large groups of full-grown specimens, preserved in their imbedded condition, the summits of the shells seem always to lie a little beneath the surrounding level of the whale's skin, but not nearly to the extent here just inferred. Nor can I believe that the epidermis of the whale had ceased being formed under these specimens, whilst it had gone on being formed all round them, to the thickness of between four and five inches, and that it had subsequently disintegrated to this same thickness,--which processes would account for the summit of the shell being still on nearly a level with the surface of the whale. The view which seems to me most probable, is, that the rapid downward growth of the shell, besides indenting the whale's skin, at the same time slowly pushes the whole shell out of the skin, and thus continually exposes the summit to the wear and breakage which seems to be necessary for its existence. On this view, the very peculiar form of Tubicinella, which is retained during life, namely, the slightly greater width at top than at bottom, is beautifully explained, viz., for the sake of facilitating the protrusion of the shell; for the ordinary conical shape of sessile cirripedes, with the apex upwards, would have rendered the pushing out of an imbedded shell almost impossible; on the other hand, we can see that the likewise very peculiar, concentric, prominent belts may be necessary to prevent too easy protrusion.

Fossil Species.--I do not believe that this genus has hitherto been found fossil. The Tubicinella maxima of Ch. Morren, said to have been found (see Bronn, Index Palæontologicus) in the chalk of Belgium, I have good reason to believe does not really belong to this genus.

11. Genus--XENOBALANUS. Pl. 17, fig. 4 a-4 c.

XENOBALANUS. Steenstrup. Videnskabelige Meddelelser. Aaret, 1851.

SIPHONICELLA (sine descript.) Darwin. Monograph on the Lepadidæ, p. 156 (1852).

Shell almost rudimentary, star-formed, composed of six compartments, with a long peduncle-formed body rising from the middle: opercular valves none.

Hab.--North Atlantic Ocean, attached to Porpoises; Mus. R. T. Lowe, Steenstrup.

This Cirripede, in appearance the most anomalous of its family, has affinities distinctly pronounced. Four years ago the Rev. R. T. Lowe sent me some specimens, which he had obtained from a porpoise between Madeira and England; and I named them in MS. Siphonicella, from their relationship to Tubicinella,--a fact which I mention only because Sir C. Lyell has alluded to this genus under the above name (without any description), in his anniversary address to the Geological Society, as have I, in my volume (p. 156) on the Lepadidæ. Since that time Professor Steenstrup has described and named the genus, fully recognising its place and affinities, and has most kindly sent me a magnificent group of specimens.

This genus singularly resembles, in general appearance, some of the pedunculated Cirripedes, so much so that in the specimens sent me by Mr. Lowe, in which the almost rudimentary shell was, from disintegration and its deep imbedment, not plainly visible, I did not in the least doubt that I was examining a new genus of Lepadidæ. I may mention, as a proof how truly all the parts and organs are correlated in Cirripedes, that I was at first in despair when I found a species to all appearance pedunculated, with its labrum not bullate, its palpi of large size, its third pair of cirri totally unlike the fourth and succeeding pairs, and with only a single layer of muscles round the peduncle; but when, in addition, I found that there were branchiæ, and that these were double, I felt convinced that I was dissecting a disguised sessile cirripede, and that its true place was near Coronula: soon, I found the imbedded and almost rudimentary shell, of which a mere fragment would equally well have declared the true position and relationship of the whole animal. Though Xenobalanus, in external aspect, is so completely masked, yet in its habits, namely, in living attached on Cetaceans, as in its essential structure, it displays its real affinities. In the course of the following description, it will be seen that in the shell, the affinity is almost equally close to Coronula and Platylepas, but that, considering the whole animal, the affinity is somewhat closer to Tubicinella. Xenobalanus may indeed be described as a Tubicinella without opercular valves,--with the opercular membrane thickened down to the basis,--and with the shell, excepting the few last-formed basal zones of growth, almost wholly removed by the breakage of its upper end; this remnant of a shell, however, presenting some strong points of resemblance to Coronula.

1. XENOBALANUS GLOBICIPITIS. Pl. 17, fig. 4 a-4 c.

XENOBALANUS GLOBICIPITIS. Steenstrup. Videnskabelige Meddelelser fra den Naturhist. Forening i Kjöbenhavn, for Aaret, 1851. Tab. 3, fig. 11-15.

General Appearance.--The shell is in an almost rudimentary condition, and appears like a small white irregular star, imbedded up to its top in the skin of the porpoise. Out of this thin, star-shaped shell, a cylindrical, flexible, peduncle-formed body springs, which forms the main part of the animal; it is narrow where coming out of the central cavity of the star, but soon acquires its full diameter; at the upper end it has a reflexed hood, and hence is broader, and this has the appearance of forming a capitulum, like that of a pedunculated Cirripede. This pseudo-capitulum is formed by a membranous reflexed collar or hood, which is very narrow at the lower end of the orifice, close under the mouth, and becomes wider and wider towards the upper and carinal or posterior end of the orifice; hence the lower reflexed edge of the hood is only slightly oblique or even nearly transverse. The orifice leading into the sack is large, and nearly in the same straight line with the peduncle; it is a little hollowed out in the middle at the upper end, and on each side of this medial hollow, there is a small rounded projection or horn, not perforated, but hollow, as may be seen by turning up the hood and looking at its under side. These two little horns curiously bring to mind the ear-like appendages in Conchoderma aurita (Otion), but these latter are perforated, open into the sack, and point outwards. The peduncle-formed body answers, as we shall presently see, to the main part of the shell in Tubicinella, and the hood, as it would appear, to the lips of the sack-aperture, which project between its scuta and terga; of these valves there is not here a trace. The whole surface is smooth, and is formed by rather thin membrane, of an orange colour; but from the colour of the underlying corium, the whole appears of a dark chocolate red, the reflexed hood being rather lighter coloured. It is singular how closely the colour resembles that of some dark varieties of the above-mentioned Conchoderma aurita, and likewise of Anelasma squalicola, both pedunculated Cirripedes, having oceanic habits, and destitute, to a remarkable degree, like Xenobalanus, of shelly valves.

The largest specimen which I have seen was very nearly two inches in length: in this specimen the star-shaped shell measured, from extreme point to point, nearly a quarter of an inch in diameter, but the internal cavity only about one eighth of an inch. This latter measure gives also the diameter of the peduncle, where coming out of the shell; the diameter just beneath the hood, was in this same specimen rather more than a quarter of an inch, and therefore greater than the diameter of the points of the shell. The depth of the shell from the upper rim to the basal membrane, in one specimen which I measured, was only one twentieth of an inch, and this specimen had its pseudo-peduncle one inch and three quarters in length, consequently thirty-five times as long as the shell was deep.

Structure of Shell.--The almost rudimentary shell (fig. 4 b) consists of a small, thin, six-rayed disc, formed of six compartments, each of which, instead of being outwardly convex, as in ordinary Cirripedes, is deeply bowed inwards. The narrow sutures (s s) separating the six compartments, run along the middle of the six rays, each ray being composed of the bowed ends of the walls of the adjoining compartments. The rays are a little curved towards the carinal end of the shell. It is remarkable that the rostrum is smaller and less deeply folded inwards than the other compartments, and the lateral compartments are a little smaller than the carino-lateral compartments, which is exactly the reverse of what is usually the case. Only about four zones of growth have been preserved in any specimen, and consequently the shell is very nearly of the same diameter at the top and bottom; for the upper end of the shell is rapidly removed, as in Tubicinella, by the scaling off of the upper rims of the sheath, and by the disintegration of the walls. The zones of growth are commonly not piled exactly over each other, but rather obliquely, as represented in fig. 4 b. Each zone projects, forming a prominent, sharp, toothed ridge round the shell. In Coronula (Pl. 16, fig. 6) and its allies, the outer lamina of the wall is formed by the union, a little above the basal margin, of ledges running along the sides of the longitudinal septa. In Xenobalanus (Pl. 17, fig. 4 c) similar ledges are less perfectly joined, and apertures seem always to be left in transverse rows under the transverse toothed ridges, which latter are best seen in fig. 4 b. The apertures, of course, are covered by membrane. The transverse ridges are surmounted by knobs arising from the longitudinal septa; and the knobs themselves are capped by other little heads, which are not represented in the drawing. Owing to these projections, and to the prominence of the transverse ridges and of the longitudinal septa, the external membrane is attached so firmly to the shell that even with the aid of caustic potash it can hardly be separated.

The internal cavity of the shell is small: it approaches a hexagon in shape, with the rostral side very short, and the lateral sides curved inwards. It is lined by a rather thick sheath, which descends very near to the basal membrane; the sheath is divided into very distinct, successive convex zones of growth. The external membrane of the pseudo-peduncle is attached with remarkable strength to these rib-like zones of the sheath. The alæ (a in fig. 4 b) are represented by mere angular shoulders, received into very slight notches, and placed at the inner ends or entrances of the double walls, or rays as I have called them. With respect to the radii, they also are in an extremely rudimentary condition; but a thin layer of shell, apparently continuous and homologous with the sheath, extends from the sheath along both sides of each ray, and on the rostral side (whence the radius ought to arise), about half-way from the end of the ray, gives rise to a projection or ridge (d, in fig. 4 b) which runs from the top to the base of the shallow shell. From this longitudinal ridge, septa, parallel to the basis, extend to nearly the extremity of the ray or double wall. These represent the radii; but they never grow, so as to increase the diameter of the shell. These radii evidently correspond to the additional or pseudo-radii in Coronula, which in that genus lie between the parallel, as here, and folded parietes. Of the true radius, having the same thickness as the paries, I here saw only traces in an internal, very slight, longitudinal ridge running up the shell, close to the outer extremity of each ray or double wall.

The membranous Basis is united all round to a rather wide flap of membrane which is inflected from the outer surface of the shell. The cement-glands appear to be mere enlargements of the cement-trunks, which latter extend in two nearly straight and parallel lines. From each gland two cement-ducts proceed, one of which runs parallel to the cement-trunk.

The pseudo-peduncle, forming the main part of the animal, has, as far as external appearance is concerned, been sufficiently described. The part forming the hood apparently answers to the protuberant lips of the operculum, and the lower part to the sub-cylindrical shell of Tubicinella; both shell and peduncle in the two genera being wider at top than at bottom. If in imagination we chip away (an action always in progress) the whole upper part of the shell of Tubicinella, leaving only two or three zones of growth at the base, we shall convert it into a Xenobalanus, with every internal part and organ occupying the same relative position: for it should be borne in mind that the shell of Tubicinella is lined close down to the basis by the opercular membrane, and this is strictly comparable with the outer membrane of the pseudo-peduncle of Xenobalanus. The body, as in Tubicinella, is attached in a vertical position, with the longer axis of the thorax and of the much elongated prosoma extending in the direction of the longitudinal axis of the pseudo-peduncle. The point of attachment of the body to the lower part of the hood is much elongated, but presents the usual muscles running to near the base of the labrum and embracing the prosoma. The adductor scutorum muscle is well developed, and is placed close beneath the mouth, where the collar or hood commences folding over: hence, no doubt, the lower end of the large and long orifice into the sack can be closed by the adductor; but the upper end probably can only be blocked up by the outer surfaces of the curled cirri. The scuta, I may add, if such had existed, would certainly have covered the point where the adductor muscle is attached to the exterior membrane. The sack extends down to within the almost rudimentary shell: the tunic lining it is unusually strong; indeed, in the reflexed hood-like portion, it is as strong as the properly external membrane. The latter seems to be moulted in large strips, and not in a single piece, like the opercular membrane in Balanus: just above the shell, fragments of three or four of these outer coats are retained by their very firm attachment to the sheath. The two layers of corium, lining the outer membrane of the pseudo-peduncle and the inner tunic of the sack, instead of being, as usual, united almost continuously together, stand some little way apart, and are connected by longitudinal septa; hence, in a transverse section, especially of the lower part, the sack is surrounded by an irregular ring of square tubes of corium. The muscles surrounding the sack and imbedded in the inner fold of corium, are very thinly spread out; they branch, and even sometimes cross each other; they are more numerous at the carinal and rostral ends, but certainly cannot be said to form six (or five) bundles, as in all other sessile cirripedes. Some of the fasciæ extend down to the very basis, and some up to the summit, to near the two little horn-like projections. I could not perceive any transverse striæ on these muscles. Altogether, they are very weak, and cannot have much power in moving the whole peduncle-like body.

Branchiæ.--These are largely developed: they are attached to two approximate, longitudinal, fleshy crests, which extend more than half-way down the sack, along the carinal margin. Each branchia is double, the two folds being united where attached in a transverse line across the sack, on a level with the attachment of the body. The inner fold is much smaller than the outer; not extending half so far down the sack, and not extending so far transversely; it is also hardly at all plicated. The larger and plicated fold extends down considerably below the lower end of the prosoma, and altogether fully equals one third of the entire length of the animal, measured from the shell to the summit of the orifice. Both folds are formed of very delicate membrane.

Mouth.--Labrum unusually prominent, as measured from its basal margin to the crest, which is but slightly notched, hairy, and without teeth. Palpi broad, heart-shaped, clothed on their inner sides by a thick brush of spines, which here, as on the other gnathites and cirri, are almost all doubly serrated. On the outer margin of the palpi there are a few longer spines. Mandibles villose, with five teeth, of which the fifth is very small and of irregular shape: the inferior angle is broad and pectinated. There are no intermediate teeth between the second, third, and fourth teeth, as in the three foregoing genera. Had I not known that the lower main mandibular teeth were always laterally double in the Balaninæ, and had I not observed how obscure this structure was in Coronula and Tubicinella, I should have overlooked the merest vestiges of double teeth in the present genus; indeed, in some specimens the teeth seemed to be absolutely single. The maxillæ are villose: their edge exhibits a trace of being notched under the two great upper spines. The outer maxillæ are bilobed, but not very plainly: between these organs there is no little prominent mentum, as in the three previous genera.

Cirri.--The cirri are short, particularly the three anterior pairs. The segments in all are singular, from being so much compressed, so short, and of such great breadth; they are protuberant in front. In the second and third cirri, the broad lateral faces of the segments, with the exception of the posterior face of the posterior ramus, are almost bare of spines. In the three posterior pairs of cirri (Pl. 29, fig. 6), the segments are protuberant in front, and support three pairs of short thick spines, with an intermediate tuft; the dorsal tufts are unusually small: their pedicels are remarkable from the upper segment, and the upper part of the lower segment, being produced into a rounded protuberance, dotted with spines: I have met with a similar structure only in Scalpellum vulgare. In the third pair (fig. 5) there is only a trace of this structure; and in the second pair the anterior margin of the pedicel is straight, and clothed with three tufts of bristles. The pedicel of the first cirrus is very broad, and clasps the mouth.

The cirri and mouth are dark chocolate red, like the outside of the animal and the upper part of the sack. The thorax is redder and paler. The four posterior articulations of the thorax are straight and transverse; the next segment, or that corresponding with the second pair of cirri, is slightly inflected, in the usual way, towards the prosoma. The prosoma is pale coloured, extraordinarily elongated, and bluntly pointed; it extends down (see the dotted outline in Pl. 17, fig. 4 a) about one third of the length of the whole animal. The orifice leading into the acoustic sack forms a freely depending little point beneath the basal articulation of the first cirrus. The stomach in the uppermost part is deeply and closely plaited longitudinally, but has no cæca; it runs down (externally coated, as usual, by the testes) to the lower point of the prosoma, and is then doubled back on itself, so that it is very long.

Generative System.--The probosciformed penis is short and thick, and covered with very minute tufts of bristles: there is no knife-edged projection at its dorsal base. The vesiculæ seminales are much convoluted and of great length. The ovarian tubes form a small sheet within the rudimentary shell, in the normal position, over the basal membrane; and likewise higher up between the two folds of corium surrounding the pseudo-peduncle; they do not, however, appear to occur round the lower part of the peduncle: they extend highest on the rostral and carinal sides, and lowest on the two lateral faces. The ova are wonderfully numerous; they are 15/2000ths of an inch in length: they form, instead of two thin lamellæ, two almost cylindrical packets, which are held together by most feeble membrane. Each packet, in the upper part lies between the two folds of the branchiæ; and in the lower part, is embraced only by the larger outer fold. The two packets of eggs sometimes cohere together at their lower ends.

Imbedment.--The shell is imbedded up to its summit, but the shell is very shallow. The imbedment seems due either to the compression of the epidermis of the porpoise, or to its formation beneath the shell having been checked; the outline of the true skin under the dark-coloured epidermis is not in the least affected. The epidermis fills up the bay-like spaces formed by the inwardly folded walls, and firmly adheres to them.

Affinities.--This genus presents very varied affinities to Tubicinella, Coronula, and Platylepas. To the latter it is more especially allied in the compartments, being singly folded inwards, though the sides of the folds are not here closely pressed together, as in Platylepas: in both these genera the fold is less deep in the rostrum, of which fact, in Platylepas, the final cause is evident, but here there seems no cause, excepting the simple one of affinity. Xenobalanus is further allied to Platylepas, in the lesser size of the inner fold of each branchia, compared with the outer, and in the structure of the cement-glands, and to a certain extent in that of the sheath. To Coronula the special alliance is shown by the remarkable character of the pseudo-radii lying between the parallel and adjoining walls, and in the general character of the cirri: in Coronula we have the terga sometimes quite aborted, and the scuta of small size, thus exhibiting a tendency to the entire absence of opercular valves, so remarkable in Xenobalanus. To Tubicinella, the alliance is still more plainly shown in the external shape of the whole animal, wider at top than at bottom,--in the opercular membrane descending almost to the very base--in the relative positions of the different parts and organs--in the upper end of the shell continually scaling off--in the prominence of the transverse external ridges--in the sheath being divided into successive zones of growth, and being prolonged nearly to the basal membrane--and in the edges of the alæ being smooth. Internally, the resemblance is also plainly shown, in the strength of the internal tunic of the sack--in the branchiæ springing from two approximate fleshy crests--in the freely depending acoustic orifices--in the form of the thorax and prosoma--and consequently of the alimentary canal.

Seeing the state of the almost rudimentary shell, it is not difficult to imagine its total disappearance. Thinking of this, it occurred to me to doubt for a few minutes, whether Anelasma, described in my volume on the Lepadidæ, which presents many points of resemblance with Xenobalanus,--viz., in colour, in the strength of the internal membrane of the sack, in the size of the orifice with its thin membranous margin, in the entire absence of opercular valves, and in epizoic habits,--might not in truth be a sessile cirripede, in an extremely altered condition; for the cirri of Anelasma are in so rudimentary a state, and the mouth in so modified a condition, that the internal characters by which pedunculated cirripedes can be distinguished from the Balaninæ, though not from the Chthamalinæ, are almost lost. But if Anelasma had belonged to either of the two sub-families of the Balanidæ, the sack would have penetrated almost to the bottom of the peduncle; there would have been only a single layer of longitudinal muscles round the peduncle; and there would not have existed ovigerous fræna. I believe that Anelasma and Xenobalanus are only analogically connected, being no more related together by true affinity, than any other two genera in the Lepadidæ and Balanidæ.

Sub-Family--CHTHAMALINÆ.

Shell with the rostrum having alæ, but without radii: rostro-lateral compartments without alæ on either side: parietes not porose.

Mouth with the labrum bullate; palpi hardly touching each other: third pair of cirri with the segments resembling those of the fourth pair.

The shell in this sub-family consists of four, six, or eight compartments, with the addition, in Catophragmus, of several whorls of supplemental compartments or scales, like those forming the lower part of the capitulum in Pollicipes. The rostrum has alæ and no radii; in shape and size it resembles the carina. The rostro-lateral compartments are destitute of alæ; in all cases they overlap the adjoining compartments, and have radii (when such are developed) on both sides. In the genus, Pachylasma, however, the shell must be looked to very young, in order to detect this normal structure, for soon the true rostrum and rostro-lateral compartments become blended together, making a compound rostrum, destitute, as in the Balaninæ, of alæ, but furnished with radii. The parietes are never porose, nor furnished with regular symmetrical ribs (representing the longitudinal parietal septa) on their inner surfaces: sometimes, however, on the basal internal edges, there are some irregular depending points. In conformity with the simplicity of the parietes, the Radii (which are seldom much developed) have likewise a simple structure; and often are merely formed by the simple lateral growth of the parietes. The scuta and terga are articulated together more deeply than is usual in the Balaninæ; and the terga never have a long spur.

Looking to the animal's body. The Labrum is always swollen and bullate, and though hollowed out, is never notched in the middle. The Palpi are rather small, and have not their tips nearly touching each other. The mandibles generally have their lower main teeth laterally single, though sometimes they are double: the inferior angle is always pectinated. The maxillæ are always notched under the upper pair of great spines. Of the Cirri, the third pair much more closely resembles, in external structure and powers of movement, the fourth than the second pair, though sometimes a few of the basal segments, especially on the anterior ramus, are thickly covered with bristles, as on the segments of the second pair. In three species belonging to two genera, there are caudal appendages, resembling those generally present amongst the Lepadidæ, but never found in the Balaninæ. The Branchiæ are generally smaller than in the Balaninæ; and are sometimes quite rudimentary.

In the introductory description (p. 152 and 176) of the Family Balanidæ, I have already discussed the relations of the Chthamalinæ to the Balaninæ, and of the several genera to each other, so that I need not here re-enter on the subject.

12. Genus--CHTHAMALUS. Pl. 18, 19.

CHTHAMALUS. Ranzani. Memoire di Storia Naturale, 1820.

EURAPHIA. Conrad. Journal Acad. Nat. Sc. Philadelphia, vol. 7, 1834.

Compartments six: basis membranous, but sometimes in appearance calcareous, owing to the inflected parietes.

Distribution mundane; attached generally to littoral rocks and shells.

This, the typical genus, is the largest and widest distributed group of the sub-family Chthamalinæ. The founder of the genus apparently did not perceive its essential character; Savigny, however, as is evident from the excellent figure in the great work on Ægypt, perfectly understood the difference between Chthamalus and Balanus. I was first indebted to Dr. J. E. Gray for explaining to me this difference; but the only published account which I have met with is in a paper by the Rev. R. T. Lowe,[130] in which he states, on the authority of Mr. Clark of Bath, that in Chthamalus the anterior compartment or rostrum has alæ like the posterior compartment or carina, the anterior or rostro-lateral compartments being destitute of alæ. These characters being exactly reversed in Balanus, as I have already explained (p. 176) under the sub-family of Balaninæ.

[130] 'Zoological Journal,' vol. 3, p. 76, 1828.

The shell, owing apparently to its containing much animal matter, is particularly subject to disintegration; and when thus much affected it is quite impossible to distinguish the species by external characters. It is, in fact, best to cast on one side external appearance, though when the shells happen to be well preserved, each species has its own peculiar aspect. We have in this genus smooth and plicated, cylindrical and depressed varieties of most of the species. The development of the radii is very apt to vary, and even the compartments often become so completely united and calcified together that the sutures are almost or quite obliterated. A more serious difficulty in discriminating the species, arises from the fact of the opercular valves, not only varying extremely in external appearance in consequence of the greater or less disintegration of their apices, and consequent exposure of their articular ridges and furrows (compare fig. 1 a, 1 b, 1 c, in Pl. 18), but from their truly varying in outline with the varying shape of the shell: this latter circumstance is probably due to the opercular membrane which unites the valves to the shell being very narrow, and in consequence, differences in the shape of the shell affect the opercular valves, in a manner and to a degree to which the Balaninæ are not subject (compare fig. 1 e, 1 f, 1 h, in Pl. 18). The scuta, on the other hand, differ to an unusually slight degree in the different species. In the common Chthamalus stellatus, which abounds on the southern British shores, the whole external aspect of the shell is often so completely masked, owing to its varying shape, its obliterated sutures, its deeply disintegrated and punctured surface, and by the corroded condition of its opercular valves, that I have found this species, in the collections of naturalists who have attended to cirripedes, arranged actually on the same tablet, mingled with specimens of Balanus balanoides. I have myself several times found it less troublesome to discriminate these two genera by the included animal's body than by the shell,[131] though the latter, when well preserved and developed, possesses such obviously well-marked characters: the same thing has occurred to me with some of the other species.

[131] It will be found ultimately to save time and trouble, to soak for half an hour in hot caustic potash, a specimen out of each group of shells to be examined, and then well wash and brush the separated valves and compartments; this process has been followed by me with all the species here to be described.

General Appearance.--The shell is generally depressed, but sometimes, when growing in groups, cylindrical. The surface is either smooth or longitudinally folded; and, as already stated, very apt to be deeply disintegrated. The radii, when developed, are narrow, with their summits oblique and rounded; but they are often quite absent, and sometimes even the sutures are almost obliterated. The rostrum and carina are of the same shape and size, and the two lateral compartments on each side are of nearly equal breadths. The orifice is generally sub-rhomboidal, being widest towards the carinal, instead of towards the rostral end, as is usual in Balanus: but in Chthamalus fissus the orifice is narrow and elongated. The opercular valves have their apices generally disintegrated and worn away, and are then seen to be deeply locked together. The colour of the shell is dirty white or dull purplish-red or brown; but in C. intertextus rich violet-purple. The species are small, not often exceeding half an inch in basal diameter, with the exception of C. Hembeli, of which I have seen a specimen two and three quarters of an inch in diameter.

Scuta.--These present no particular character, excepting in most cases the large development of the articular ridge, and sometimes the presence of a furrow above the articular ridge, of which only traces can rarely be detected in Balanus; hence in these cases, as in C. Hembeli (Pl. 18, fig. 5 a, 5 c) and scabrosus (Pl. 19, fig. 2 a, 2 c), the line of articulation between the scutum and tergum is more complicated than is usual. There is generally a slight pit, sometimes even furnished with small crests, for the lateral scutal depressor muscle: in C. scabrosus (fig. 2 d, q) a part of this muscle is attached to a small pit at the basi-scutal corner of the tergum,--a fact of which I have observed no instance in any other genus. In C. intertextus the terga and scuta are calcified together, without even a suture being visible on their internal faces. In C. Hembeli the valve is externally marked by a few longitudinal furrows.

The Terga, like the scuta, have a prominent articular ridge and deep furrow. In many specimens of C. stellatus and in C. scabrosus the valve is narrow: in C. fissus it is triangular and nearly equilateral. The crests for the depressores muscles are well developed: in C. scabrosus (Pl. 19, fig. 2 d, p) these crests are united into a plate, which, together with the outer lamina of the valve, forms a deep narrow pit: in C. Hembeli the crests are furnished with small sub-crests. The opercular membrane is narrow; it is sometimes furnished with a few minute spines.

Structure of Parietes.--The parietes are solid, and composed of successive layers of shell; the inner surface varies in condition in the same species, being either smooth or marked with branching impressed lines, or mamillated, or often irregularly punctured for the entrance of tubuli. Owing to these tubuli, the walls, when externally disintegrated, often become punctured. In certain depressed varieties of both C. stellatus and scabrosus the walls are supported by irregular depending columns, placed along either one side or both sides of the sutures. In C. intertextus we have the remarkable character of the wall of the shell growing (I presume after a certain age) almost rectangularly inwards, thus forming a rather wide, flat, calcareous rim round the central basal membrane. In C. Hembeli the internal basal edges of the parietes, in one moderately young specimen, were rugged with irregular points, but presented no other remarkable appearance; but in five old and very large specimens, the whole basis was calcareous, being absolutely continuous with the inner lamina of the parietes, showing that the latter had grown flatly inwards all round, and had then become confluent in the middle, so that there was no longer any basal membrane; excepting, no doubt, that which had existed in the younger stage, and which would be preserved in a functionless condition between the surface of attachment and the inflected parietes.

When an opercular valve or compartment is dissolved in acid, layers of tissue are left, and these are seen to be penetrated by tubuli, which enter at the punctures before mentioned on the inside of the shell: these tubuli often stand in groups of three or four together; they are about 1/10000th of an inch in diameter. Besides these irregularly scattered tubuli, there are in the opercular valves of C. antennatus, innumerable smaller parallel tubuli, running to the external investing membrane.

Structure of the Radii and Alæ.--The radii, when developed, are always rather narrow. Their recipient furrows are generally nearly as broad as the radii themselves. Their edges are either quite smooth, as in C. antennatus; or very finely crenated; or, as in C. dentatus and Hembeli (Pl. 18, fig. 3 a, 5 a), so strongly crenated as to make the suture, both externally and internally, toothed: in these two species, the radii are ribbed in transverse lines parallel to the basis, each rib corresponding with one of the projecting and interlocking teeth on the sutures. In C. intertextus, and much less plainly in most specimens of C. scabrosus (Pl. 19, fig. 1 a, 2 a), we have a structure in appearance very different, for the radii here consist of several very oblique plates, (i. e. nearly parallel to the parietes) on both sides of the sutures, which are interfolded or locked together: I believe that this structure is a mere modification of that in C. dentatus and Hembeli, the transverse ridges on the radii of those species being here developed into oblique plates. We shall hereafter meet with a similar structure in the genus Verruca; to which genus, until meeting with these two species of Chthamalus, I had thought that the interfolding sutures had been confined. The alæ have their edges generally finely crenated: during diametric growth (when such takes place), they are rarely added to above the level of the opercular membrane, and hence their summits are oblique: in C. intertextus, however, the alæ are laterally added to above the opercular membrane, and their recipient furrows are likewise added to, of which fact I have seen no other distinct instance in any genus; hence on both sides of the sutures, in the sheath of this species, the lines of growth are upturned. In some much disintegrated specimens, both of C. stellatus (var. depressus) and of C. antennatus, the radii have been corroded away, and the diametric growth is effected exclusively by the growth of the alæ, which are moreover much exposed, and rendered conspicuous. The sheath descends a moderate distance down the shell. When a shell is boiled in potash, the sutures (excepting when abnormally calcified together, as very often happens with some species) always fall apart, showing that the union is simply by animalised matter.

Basis.--The basis is always membranous; but we have seen, in C. intertextus, that the walls form a flat ledge all round the base, and that in old specimens of C. Hembeli, they grow so far inwards and become so completely confluent, that they might most easily be mistaken for a true calcareous basis. I may add, that in one elongated specimen of C. stellatus from La Plata, the walls had likewise grown rectangularly inwards, forming a flat base, and had then turned upwards in the middle, forming a medial crest, with the edges not quite calcified together. The true basal membrane is very obscurely divided into concentric slips. I observed in several species, attached to the lower surface, an excessively fine network, quadrangular or hexagonal, of yellow vessels, which seemed insensibly to pass into the sheets, discs, and globules of cement, by which the membranous basis adheres to the supporting surface. I saw, in C. antennatus, numerous irregular, bifurcating, and inosculating cement-ducts, of unequal diameter, often crossing each other, and sending off branches ending in points: the older ducts, instead of being solidly filled up with cement, were only divided by septa. I did not succeed, in any species, in discovering the cement-glands.

Mouth.--The labrum is slightly bullate, with the middle portion depressed, but not forming a notch; in some species it is hairy, and in some pectinated with short spines. The palpi are of moderate size. The mandibles have from three to five main teeth, the number sometimes varying even in the same species: the lower teeth are either plainly double laterally, or very obscurely double, or to all appearance quite single: a rather large lower portion of the mandible is finely pectinated. The maxillæ are always notched under the two or three large upper spines: the notch bears some fine spines: beneath the notch there are some large spines, and at the inferior angle some smaller ones.

Cirri.--The first and second pairs are always very short compared with the four posterior pairs. The rami of the first pair are slightly unequal. The third pair, in length and arrangement of the spines, very closely resembles the three posterior pairs; in C. intertextus, however, the few basal segments, chiefly on the anterior ramus, are thickly clothed with bristles, like the segments of the second cirrus. In C. antennatus (Pl. 29, fig. 2), the anterior ramus of this same third pair is usually (one single specimen being excepted) much elongated, having at least twice as many segments as the posterior ramus, but the number is variable; and these segments, either all, or only the upper ones, instead of having their spines regularly arranged in pairs, in a double row, are surmounted each by a circle of spines: I suspect that these elongated rami of the third cirrus act as antennæ. It can hardly be an accidental coincidence, that certain genera, as Lysmata and Pandalus, amongst the Macrourous Crustaceans, have the same leg (homologically the second thoracic limb) elongated and antenniformed. Certain varieties of C. stellatus and cirratus, also, have the anterior ramus of this same third cirrus considerably elongated. We are thus reminded of the remarkable variability in the numbers of the segments, and in the arrangement of their spines, in the cirri of Tetraclita porosa; in that species, however, it was chiefly the terminal segments of the posterior ramus of the third cirrus which were so highly variable. The three posterior pairs of cirri in Chthamalus support from three to five pairs of main spines on each segment, the number often varying in the same species, with some minute intermediate bristles. The dorsal surfaces of these segments, in some of the species, are serrated in an upward direction.

Body, &c.--The body does not present any particular character: in C. scabrosus there is a slight ridge running from the base of the first cirrus towards the adductor scutorum muscle: this ridge is clothed with a few hairs; there are also some hairs at the carinal end of the sack. In C. dentatus, also, there are hairs on the outer tunic of the prosoma. In two species which I opened, there were no cæca to the stomach. The ova vary in length from 13 to 14/2000th of an inch in length; they are packed in two lamellæ lying on each side of the animal's body. The larva just escaped out of the egg, in C. stellatus, scabrosus and dentatus, had a large probosciformed mouth.

Branchiæ.--These present a very singular amount of difference within the limits of the same genus. In C. stellatus and antennatus we have a simple fillet, tapering a little, barely plicated, and about half, or more than half, as long as the sack; in C. scabrosus the branchiæ are entirely aborted, or are perhaps represented by the slight hairy ridge at the carinal end of the sack: in C. dentatus, on the other hand, each branchia consists of two large folds, barely plicated, almost covering the whole side of the sack, so that here the branchiæ are developed to an unusual degree, more than in Balanus, and as in Coronula and its allies: in the same manner as in these latter genera, the outer fold is considerably larger than the inner fold.

Affinities.--C. intertextus is the most distinct species of the genus, as shown by the peculiar radii and alæ, by the scuta and terga being calcified together, by the character of the third pair of cirri, and by the inflected parietes forming a ledge round the membranous basis; but in this latter respect C. intertextus resembles C. Hembeli. C. Hembeli, in its serrated radii, is closely related to C. dentatus; and this latter species differs in the structure of its radii only in degree from certain varieties of C. stellatus. Lastly, C. intertextus, in its peculiar radii, closely resembles C. scabrosus, and this latter species does not differ much from the other species. Hence the genus Chthamalus has no claims to be subdivided into smaller genera.

Range.--The species are found all round the world, from (as far as I have seen) 54°-55° north, to Cape Horn, in 55°-56° south. All the species, of the habits of which I know anything, are littoral; and in many parts of the world are excessively numerous, quite covering large spaces of the coast-rocks, and often coating the coast-shells. Chthamalus dentatus is littoral, like the other species; but it often lives attached on Balanus tintinnabulum and amphitrite, on the bottoms of ships arriving in British ports from the west coast of Africa. I do not know of any instance of more than two species occurring in the same region. Some of the species have large ranges: C. scabrosus extends from the Falkland Islands and Tierra del Fuego to Peru; and C. stellatus has an enormous extension over almost the whole world, excepting the west coast of South America and Australia. I do not believe any species of the genus, owing probably to their littoral habits, have hitherto been found fossil.

1. CHTHAMALUS STELLATUS. Pl. 18, fig. 1 a-1 h.

LEPAS STELLATA. Poli. Testacea Utriusque Siciliæ (1795), Tab. 5, fig. 18-20.

---- DEPRESSA (var.) Ib., Tab. 5, fig. 12-16.

CHTHAMALUS STELLATUS. Ranzani. Memoire di Storia Naturale (1820), Tab. 3, fig. 21-24.

---- GLABER (var.) Ranzani. Ib.

---- STELLATUS. Philippi (!). Enumeratio Mollusc. Siciliæ.

LEPAS PUNCTATUS. Montagu (!). Testacea Britannica (1803).

Shell white or gray, generally much corroded and punctured: radii (when present) narrow, with their sutural edges most finely crenated; tergum with the crests for the depressor muscle depending barely beneath the basal margin.

Var. (a, communis) fig. 1 a, 1 f: Shell conical depressed, upper part corroded, walls folded, sutures moderately plain or obliterated; radii not developed; orifice broadly oval.

Var. (b): Shell elongated, sub-cylindrical; sutures obliterated; surface much corroded; orifice almost circular.

Var. (c, communis) fig. 1 c, 1 e, 1 h: Shell conical, folded, sometimes covered by membrane; radii developed, narrow; orifice sub-hexagonal, toothed.

Var. (d, fragilis) fig. 1 d: Shell conical, smooth, thin; compartments easily separable, pale-coloured; radii developed, narrow; orifice large, toothed, sub-hexagonal.

Var. (e, depressus) fig. 1 b, 1 g, 1 h: Shell much depressed, surface much corroded, smooth: alæ largely exposed, marked by lines of growth: radii not present; parietes on the under side often supported by pillars; orifice sub-hexagonal.

Hab.--Southern shores of England, Ireland, Isle of Man, Mediterranean, Madeira, Cape de Verde Islands, Southern United States (Charlestown), West Indies, Brazil (Bahia), Rio Plata (Guritti Island), Red Sea, Philippine Archipelago, Coast of China, Gulf of Corea, Oregon or Northern California.

Spotted a typo or a problem in this chapter? Tell us