A Monograph on the Sub-class Cirripedia (Volume 2 of 2) The Balanidæ, (or Sessile Cirripedes); the Verrucidæ, etc., etc. (part 4 of 5)

A Monograph on the Sub-class Cirripedia (Volume 2 of 2) The Balanidæ, (or Sessile Cirripedes); the Verrucidæ, etc., etc. (part 4 of 5)

This species is very widely distributed and extremely common. On the coast-rocks of the southern shores of England it is, in parts, even more numerous than the Balanus balanoides, with which it often grows mingled. As already stated, it is often confounded in British collections with this species of Balanus, under the name of Balanus punctatus; that Montagu had this Chthamalus in view, when describing his Lepas punctatus, is certain, from his original specimen in the British Museum, but whether this was the case with his predecessor, Pulteney, in the Dorset Catalogue, I do not feel so sure. Chthamalus stellatus varies, as we shall immediately see, extremely in appearance. Some of the varieties, as var. depressus, which in external aspect are especially distinct, I have no doubt are really varieties, but whether this is the case with some of the forms from the more distant localities, is a little more doubtful; but I beg that it may be observed, that I have, in the case of every one of the varieties, and of all the specimens from distant localities, cleaned with potash and most carefully examined the disarticulated valves, and likewise dissected the included animal's body.

General Appearance.--British specimens are usually conical, and have their walls folded, corroded in their upper parts, with the radii not developed, and the sutures more or less obliterated; in this state the orifice of the shell is entire, and very broadly oval: I have seen specimens in this condition from Madeira, Brazil, and the Gulf of Corea. The shells when crowded, are rendered cylindrical, and more or less elongated, with the sutures as viewed externally quite obliterated; the surface rugged and much disintegrated; and the orifice nearly circular: in this extreme condition I have seen specimens from England, from near Genoa, and from the mouth of the Plata: the specimens from these last two localities were of remarkable size, being half an inch in diameter, and rather more than half an inch in height. Again, other British specimens (fig. 1 c), though not nearly so common, are rather steeply conical, and have not only their sutures distinct, but narrow radii are plainly developed on apparently both sides of the sutures; in this case the orifice is slightly toothed, and is rather elongated: I have seen specimens in this condition, but with their walls rather more deeply folded, from the Cape de Verde and Philippine Archipelago. Other specimens, from some unknown tropical sea, differed only in the walls being but slightly folded, and being so perfectly preserved as to be externally covered with membrane: this latter circumstance gave the specimens a peculiar appearance. In this condition were some specimens (fig. 1 d) attached to oysters sent to me by Professor Agassiz, from Charlestown; and which differed from all the others that I have seen, in the thinness and smoothness of their compartments, and in the facility with which the compartments separated from each other and from the surface of attachment: hence I have called this form, which, until finding more important differences, I must rank as a variety, fragilis: it has stronger claims than the other varieties to be specifically separated; but I suspect that it has been exposed to some peculiar modifying conditions.

Lastly, we have the variety (fig. 1 b) excellently figured and described by Poli, under the name of L. depressa: this is much depressed, with the walls thin, not folded, with the surface much corroded, with the sutures very distinct, with the radii not at all or barely developed, but with the alæ largely developed, and marked with lines of growth, resulting from the diametric growth of the shell: the orifice is hexagonal, but broadest towards the carinal end: most of the specimens, but not all, have on the under sides of their compartments rugged pillars depending from beneath the alæ, for the purpose, apparently, of supporting the much depressed shell. This much depressed variety attains a larger basal diameter (but not a greater bulk or internal capacity) than any other variety, namely, sometimes three quarters of an inch. The great peculiarities of this variety result, apparently, from its much depressed form, deeply corroded not folded walls, and considerable diametric growth; from the latter cause the alæ are largely developed; as I can find neither internally nor externally any fixed diagnostic character I have not hesitated to rank this form as a variety. Poli found his specimens mingled with the ordinary C. stellatus, on the shores of Sicily; and I collected at St. Jago, in the Cape de Verde Archipelago, some specimens nearly as well characterised, also associated with the common variety.

The shell itself is dirty-white or gray, or brown: in some varieties, however, the white is nearly pure: internally the parietes are generally tinted dull purple. The corium of the sack is dark greenish-black, with a white edge to the lips lining the aperture between the opercular valves.

Structure of Shell and Radii, &c.--The under side of the parietes is either quite smooth, or marked with slight, branching, depressed lines; or mamillated; or irregularly studded with large pores. I have already alluded to the pillars, depending from the under sides of the alæ in most specimens of var. depressus: these pillars tend to form ridges, parallel to the sides of the compartment, like those we shall presently see in certain specimens of C. scabrosus. The radii are very narrow, when best developed; their edges, when disarticulated, can be seen, when examined by a strong lens, to be finely crenated. The edges of the alæ are likewise very finely crenated.

Scuta.--The outline of these valves varies considerably in specimens taken out of the same group: we have either a nearly equilateral triangle (fig. 1 f) or the tergal margin (1 e) is much shorter than the other margins. There is always a deep depression for the adductor muscle, and a small pit of very variable depth for the lateral depressor. But the tergal margin offers the greatest variability; here we see a very prominent articular ridge or fold, having either a straight edge or a single or double prominence (fig. 1 e-1 h). In specimens in the same group we find considerable variation in these points; but the amount of difference is sometimes so great, that I long hesitated whether to rank some of the varieties as species. The Terga, likewise, vary greatly in shape and width: in some of the commonest varieties (and in var. depressus) the valve is very narrow, with the under surface channelled or concave: in other varieties the valve is much broader and flatter. The spur is but slightly developed. The crests for the depressor muscles barely descend beneath the basal margin of the valve. The articular ridge, in some varieties (as in specimens from Madeira and the Cape de Verde Islands), is extremely prominent and straight (1 f); in others, it is little prominent and deeply sinuous (1 h). This great variability in the articular margins of the scutum and tergum seems to be mainly due to the corrosion to which these valves have been subjected, and their consequently modified growth: in some specimens the articular ridge of the scutum, and in others that of the tergum, has been largely developed, in either case their mutual outlines being greatly affected.

Branchiæ.--These are narrow, hardly at all plicated, elongated, being about half as long as the sack. In a specimen from La Plata, this organ ended rather more abruptly in a point than it did in other specimens.

Mouth.--The crest of the labrum is usually hairy, but in a specimen from Bahia (Brazil) there were some very fine teeth. The palpi vary somewhat in shape, and sometimes have a row of bristles along their basal exterior margins. The mandibles usually have four main teeth, the lowest one being confluent with the inferior pectinated angle: in var. depressus, in the same individual, there were only three teeth on one side of the mouth and five on the other; the lower main teeth are laterally double, but generally one tooth of each pair is so small and obscure as to be perceived with difficulty. In the maxillæ, there are some large spines above the notch, and in the notch some fine ones: in var. depressus, and in a cylindrical var. from La Plata, there was quite a tuft of small spines above the notch.

Cirri.--The outer surface of the pedicel of the second cirrus bears a tuft of long, fine, plumose hairs: the terminal segments of the rami of this cirrus sometimes (as in the La Plata specimens) support a clump of coarsely pectinated spines. In specimens having six segments in the shorter ramus of the second cirrus, the shorter ramus of the third cirrus had fifteen segments. The two rami of the third cirrus are usually equal in length and in the number of their segments; but in the Brazilian specimen there were fifteen segments in the posterior, and twenty-six in the anterior ramus; in another specimen, fixed on a tropical Perna, there were in the two rami of this third cirrus eighteen and twenty-four segments. In the three posterior pairs of cirri each segment carries either four or five pairs of main spines: the segments vary a little in the degree to which they are elongated, being most elongated in the var. from La Plata, with an elongated shell.

Varieties.--It will have been observed, that the shell, in the specimens from several distant quarters of the world over which this species, as I believe, ranges, differs considerably in external aspect: so do the opercular valves; and so do the parts of the mouth and cirri: but I cannot make out that these differences are coordinated. Thus, var. depressus, which is so entirely different from the others in appearance, differs only internally in the presence of a tuft of fine spines above the notch of the maxillæ; and this character is found in the La Plata variety, which, as far as the shell and opercular valves are concerned, is at the other end of the scale of variation. Again, var. fragilis, from Charlestown, presents, in the animal's body, hardly any difference. The Brazilian specimens, which in the shell and operculum offer only quite common characters, have the remarkable peculiarity of a considerable difference in the length and number of the segments in the rami of the third cirrus; they, also, have the segments of the sixth cirrus considerably elongated, and the labrum finely toothed. Of these peculiarities one alone, namely, the inequality in the rami of the third cirrus, but in a lesser degree, is common to the specimens adhering to the tropical Perna, which had a shell very unlike the Brazilian variety, but which, on the other hand, differed scarcely in a single character from some other specimens from an unknown tropical sea, in which the rami of the third cirrus were quite equal. The La Plata specimens differ most in internal characters, viz., in the tuft of fine spines above the notch of the maxillæ, in the coarsely pectinated spines on the tips of the second pair of cirri, in having the segments of the sixth cirrus much elongated, and in the apex of the branchiæ being abruptly pointed; yet in the shell and operculum they were identical with certain Mediterranean varieties. From these several facts, I must believe that all the widely distributed forms here grouped together, do really belong to the same species.

2. CHTHAMALUS ANTENNATUS. Pl. 18, fig. 2.

Shell conical, generally smooth: when not deeply corroded of a pale dirty flesh-colour: sutures always distinct: radii, when present, with their sutural edges quite smooth.

Hab.--New South Wales, (Moreton Bay, 27° S.; Sydney; Twofold Bay), Van Diemen's Land (Hobart Town). Attached to littoral rocks and shells; Mus. Brit., Cuming, Darwin.

General Appearance and Structure of Shell.--Shell conical, rather smooth; when not much corroded, of a pale dirty flesh-colour; often covered by membrane; sometimes deeply corroded, extremely rugged, and then of a brown colour; in this condition not much punctured, as generally is the case with C. stellatus. Sutures almost always quite distinct; rarely the shell becomes cylindrical with the sutures obliterated. Orifice moderately elongated, sub-hexagonal. Radii rather narrow, but not so narrow as in C. stellatus, smooth, with their upper margins very oblique: when disarticulated their edges are quite smooth. The edges of the alæ are sometimes crenated, and sometimes not so, being only marked by lines of growth; they are often rather thick. The parietes are usually rather thick, with their internal surfaces smooth, and not mamillated, as is so often the case with C. stellatus. The largest specimens which I have seen, were .6 of an inch in basal diameter.

Opercular Valves.--These are hardly distinguishable from those of C. stellatus. The only very slight difference which I can point out is, that the crests for the tergal depressores are less spread out, and depend rather more beneath the basal margin of the valve; and lastly, that the surface of the tergum, just above these crests, is rather prominent.

Branchiæ: these are oblong; taper but little, and have a broad rounded end: they are scarcely plicated.

Mouth.--The crest of labrum is hairy: the palpi are square, and have no bristles along their basal exterior margins, but long ones at their truncated ends. The mandibles have three or four main teeth apparently single: the inferior coarsely pectinated portion is short. The maxillæ are deeply notched.

Cirri.--The first and second pairs, and portions of the third, are darker coloured than the three posterior pairs. The rami in both of the first two pairs are slightly unequal in length. The third cirrus is much longer than the second: in a specimen in which there were six segments in the shorter ramus of the first and second pairs, there were twenty segments in the posterior and shorter ramus of the third cirrus; and in this same individual there were no less than forty-nine segments in the anterior ramus. In another specimen (Pl. 29, fig. 2) the number of segments in the two rami of the third cirrus, was 20 and 41; in another, the numbers were 18 and 53; in several other specimens the numbers varied in about these proportions; but in one single specimen the numbers were equal. Not only did the number of segments thus vary in the two rami, but likewise the arrangement of the spines on the segments in the anterior and longer ramus; in some specimens the spines on all the segments were arranged in a single circle, and then the organ had a specially antenniformed appearance: in other specimens, some of the lower segments (in one case thirteen in number) had the spines placed in regular pairs precisely as on the posterior ramus, and as on the three posterior pairs of cirri. Under the genus I have pointed out the resemblance between this structure and that occurring in certain Macrourous Crustaceans. The pedicel of the third cirrus had its spines more crowded and irregular than on the three posterior pairs of cirri. The segments in the latter vary in bearing either three or four pairs of main spines. The whole dorsal surfaces of the lower segments of the several posterior cirri are serrated in an upward direction by short spines, but to a variable degree.

3. CHTHAMALUS CIRRATUS. Pl. 18, fig. 4 a, 4 b.

Shell white or gray: sheath and opercular valves generally clothed by fimbriated membrane: tergum, with its basi-carinal angle depending and pointed.

Hab.--Peru, Chile, Chiloe, Northern Chonos Islands. Attached to littoral rocks, and sometimes to littoral shells, often mingled with Chthamalus scabrosus; Mus. Brit., Cuming, Darwin.

General Appearance and Structure of Shell.--Shell dirty white or gray: sometimes tinted pale purple within; irregularly conical, or much depressed, or cylindrical and much elongated. Generally much corroded, sometimes well preserved and covered by membrane. Orifice rather large, of variable shape. Sutures often quite obliterated. Radii when developed narrow, with their sutural edges, as well as those of the alæ, generally very finely crenated, but to a variable degree. The membrane lining the sheath and covering the opercular valves, is remarkable from each zone being fimbriated; for this expression is more correct than to say that the membrane bears a row of spines, though the fimbriæ do approach in character to spines; sometimes, though rarely, the fimbriæ are branched. The largest specimens which I have seen (from Coquimbo and Valparaiso) were half an inch in basal diameter, and some of these were so much elongated as to be one inch in height.

Scuta.--The scuta are rather narrow: they have a somewhat peculiar appearance, from the articular furrow being wide, and from the articular ridge projecting with a uniform curvature: the pit for the lateral depressor muscle has some minute crests, of which I have seen traces in the foregoing species. The Terga vary somewhat in shape: they have the basi-carinal angle of the valve, where the narrow crests for the depressores are placed, pointed and dependent, and the surface of the valve above these crests is prominent. Altogether the opercular valves have a sufficiently distinct character to be recognised without much difficulty.

Mouth.--The crest of the labrum is not toothed; the palpi have long hairs along the exterior basal margin. The lower main teeth of the mandibles are plainly laterally double. Cirri.--The pedicel of the second cirrus is extremely broad, and on the exterior margin supports a tuft of very long, finely plumose spines: in some specimens each of the lower segments of the anterior ramus of this cirrus bore one or two very large spines, doubly and extremely coarsely pectinated. In two specimens the rami of the third cirrus were of equal length: but in one specimen (from Iquique, Peru), having seven segments in the shorter ramus of the first and second pairs of cirri, the posterior ramus of the third pair had fourteen segments, and the anterior ramus twenty-two segments. The posterior cirri have segments carrying five pairs of main spines: the dorsal surfaces of the lower segments are serrated.

4. CHTHAMALUS FISSUS. Pl. 18, fig. 6 a, 6 b.

Shell brownish, plicated; orifice twice as long as broad: tergum triangular, equilateral, with the basal and carinal margins slightly protuberant.

Hab.--California, attached to Lottia grandis. Peru(?); Mus. Brit.

General Appearance and Structure of Shell.--Shell globulo-conical, irregular, with the walls much folded. Colour brownish. Sutures generally distinct in young specimens, and nearly obliterated in full-grown individuals. Radii, when present, very narrow. The orifice of the shell, in full-grown specimens which have their summits a little worn, is narrow, much elongated, about twice as long as wide, oval or ovate, with the rostral end the narrowest: the elongation of the orifice offers almost the only character by which this species can be externally recognised. The lateral compartments are rather wider than usual in proportion to the rostro-lateral compartments. Basal diameter of largest specimen .2 of an inch.

Scuta, elongated transversely, with the pit for the adductor muscle bordered on the under side by an adductor ridge rather more prominent than usual in this genus. Terga, triangular, equilateral, with the margins slightly curved and protuberant: the basal margin is regularly and equably curved from one end to the other.

Neither the Mouth nor Cirri offer any peculiar characters distinct from the genus. I may mention, however, that the crest of the labrum is toothed, and that the segments of the posterior pairs of cirri support five pairs of main spines.

The characters by which this species differs from C. stellatus and from the other species, consist almost exclusively in the triangular and equilateral terga, and in the much elongated orifice of the shell; and these differences I believe to be of specific value. I must, however, confess that I have examined one young specimen attached to a Pollicipes elegans, in which the orifice was not nearly so much elongated, and in which the terga were not so equilateral, with the basal margin not quite equably curved, but more protuberant on the scutal than on the carinal side: from an examination, however, of only one specimen, and that a young one, I cannot decide on its specific nature.

5. CHTHAMALUS DENTATUS. Pl. 18, fig. 3 a-3 c.

CHTHAMALUS DENTATUS. Krauss (!). Die Südafrikanischen Mollusken, 1848, tab. 6, fig. 27.

Shell dirty white or brownish: sutures formed by interlocking teeth: tergum with the carinal margin protuberant.

Hab.--South Africa, Natal; West Africa, Loanda and the Gold Coast; West Indies (?). Attached to ships' bottoms and to littoral shells, and to Tetraclita serrata, Balanus perforatus, and amphitrite; often attached to Balanus tintinnabulum and amphitrite on ships' bottoms.

General Appearance and Structure of Shell.--Shell dirty white, pale brown, or gray: conical, moderately depressed: walls either broadly and irregularly folded (fig. 3 a), with the surface corroded, or (when attached to ships' bottoms and sometimes to other Cirripedes) narrowly and regularly folded (3 b), with the surface well preserved, smooth, and generally covered by thin brown membrane. These latter specimens generally have the shell more steeply conical, with the orifice rather smaller, and the radii broader, than in the first-mentioned specimens, which are attached to coast-rocks and shells, and have had their summits worn down. The sutures in all cases are tolerably distinct, and have their edges toothed and interlocked: the crenations are visible before the compartments are disarticulated, when viewed either internally or externally, but occasionally they are obscure. The radii, when best developed, are rather narrow, and of equal width on both sides of the sutures, with their summits rounded: their surfaces are finely ribbed transversely, each rib corresponding with, or rather forming a point of, the toothed edge. On the under side these teeth usually are a little hollow or are pitted: the radii, in fact, may be said to be folded, like the parietes, only more symmetrically and narrowly, so that the points in the opposed edges interlock. The edges of alæ are serrated, but more finely than the radii. The parietes are rather thin, with their under surfaces generally smooth. The sheath does not descend far down the shell. The colour of the corium lining the sack and the animal's body varies considerably, being either almost black or pale purple; and the specimens adhering to ships' bottoms are internally almost white. Of these latter specimens, I have seen some .6 of an inch in basal diameter: of corroded specimens attached to littoral shells, I have not seen one quite .4 of an inch in basal diameter.

Scuta, with the articular ridge very prominent: the pit for the adductor is deep, and there are generally some distinct, though minute, pits for the lateral depressores. The Terga (fig. 3 c) have the articular ridge very prominent; and the carinal margin is rather more arched and protuberant than in the other species.

Mouth.--The crest of the labrum is toothed: the palpi are short, truncated, with long spines arising from their ends, and along the basal exterior margin. In the mandibles the first tooth is seated rather far from the succeeding teeth: the inferior part is coarsely pectinated: the maxillæ are deeply notched. The tips of second pair of Cirri have many coarsely pectinated spines: the shorter ramus had six segments, whilst the shorter ramus of the third pair had eighteen segments: the segments on the posterior cirri carry five pairs of main spines.

Branchiæ, &c.--These consist of a double fold, the outer one being the largest, and the inner semi-circular, as has been described under the genus. In a young specimen, only one tenth of an inch in basal diameter, the branchiæ consisted of a single fold; in a specimen a little larger, there were two folds, but these were of equal size: ultimately the outer fold increases in size so as to become nearly double the inner fold. The Ovarian tubes are remarkable from their large diameter. I was surprised to observe in the specimen only one tenth of an inch in basal diameter, that the larvæ were ready to escape. On the prosoma, there are some longish hairs arranged in short rows, and some few on the membrane lining the sack, and some on the opercular membrane and valves.

It may be seen in Pl. 18, fig. 3 a, and 3 b, that I have here united two varieties considerably different in external aspect: I have done this without hesitation, inasmuch as there are intermediate forms, and as the differences are analogous with those so commonly occurring in sessile cirripedes; dependent on whether or not the specimens have been exposed to corrosion. I have seen both varieties from Natal, and both from the west coast of Africa; although the smooth, well-preserved, narrowly plicated varieties seem more common in western than in southern Africa. With respect to the range of the species, I have seen a specimen from the West Indies, but it was the variety which so commonly adheres to ships' bottoms. This variety often arrives alive in British ports; and I have seen a specimen picked up dead on the beach near Dublin.

6. CHTHAMALUS HEMBELI. Pl. 18, fig. 5 a-5 d, e.

EURAPHIA HEMBELI. Conrad. Journal Acad. Nat. Sc. Philadelphia, vol. 7, 1831, Pl. 20, fig. 6.

Shell dull reddish purple: sutures, when not obliterated, formed by interlocking teeth: basis sometimes rendered calcareous by the inflexion of the parietes: scutum with two or three furrows extending down the middle of the valve.

Hab.--California, near S. Diego, according to Conrad. Mus. Brit., Cuming.

I have seen five, old, large specimens, from an unknown locality, with their whole surfaces deeply corroded, and with most of the sutures obliterated; and three separated valves of a young specimen. From these materials, imperfect as they are, I feel no hesitation in identifying this species with the Euraphia Hembeli of Conrad, which is remarkable in several respects, and especially from being gigantic in size, compared to other members of its sub-family.

General Appearance and Structure of Shell.--The young specimen (fig. 5 b, about .7 of an inch in basal diameter) consists only of the carina, and the two lateral compartments; but these, as far as I can judge, resemble the specimen figured and described by Conrad, which was two inches in diameter. Shell depressed, spreading, surface moderately smooth, covered by brownish membrane: shell itself pale dull reddish-purple. The radii are not very narrow, with their summits rounded and very oblique: their edges are toothed, and their external surfaces are transversely ribbed, in correspondence with the interlocking points of the sutures. On the internal surface, the toothed suture is not visible, except near the base of the shell, owing to the overlapping of the alæ. The alæ have oblique summits, which are slightly notched owing to the upturned prominent lines of growth. The parietes are thick; their basal internal surfaces are rugged, with slightly branching ridges.

The old specimens (fig. 5 a) are so much corroded that not a particle of the external surface is left: one of them which was 2-3/4 of an inch in basal diameter. Shell much depressed, spreading; colour pale purple; orifice large, rhomboidal, with a slight hollow on each side for the corners of the scuta: sutures generally in part or wholly obliterated; where still preserved, the interlocking toothed structure is distinct; the sheath is strongly marked by lines of growth, and is of a dark brown colour. The carina and rostrum are of unusually large size compared with the lateral compartments; and this, as far as I can judge, must have been the case with the younger specimens. That portion of the rostro-lateral compartment which forms part of the sheath, is reduced to a mere ridge. The most remarkable character is, that all these old specimens (of which the smallest measured nearly one inch and a half in diameter) had a flat, wide, calcareous basis, which is absolutely continuous with the inner lamina of the parietes, whereas in the younger specimen there was no appearance of any tendency in the parietes thus to grow inflected. There can be hardly any doubt that in a series of specimens some would be found with the parietes first forming a flat narrow ledge round the true basal membrane (as in the following species); and that in others, this ledge would be wider and wider, till its edges met in the middle, and coalesced into a continuous plate.

Opercular Valves.--I have seen these only in the old corroded specimens (fig. 5 c, 5 d): they are locked together by remarkably strong articular ridges and furrows.

The Scuta have externally two or three impressed lines or narrow furrows, proceeding from the apex to the middle of the basal margin; these can be seen only in one of my specimens, owing to the degree to which the valves have suffered disintegration; but they are mentioned by Conrad. The basal margin is rather short compared with the other two margins. The tergal margin is remarkable from the depth of the upper furrow above the articular ridge, and from the size of the prominence (appearing like the true apex of the valve) above this upper furrow. There is a hollow for the adductor muscle, and traces of crests for both the rostral and lateral depressores. The Terga are generally but little corroded, and hence the dark brown membrane with which they are covered is well preserved; the shelly matter itself is also brown: there is only a trace of this colour in the more corroded scuta: the external surface of the terga is very smooth. The spur is pretty well developed, and is half as wide as the whole valve. The lines of growth are upturned along the carinal margin. The articular ridges and furrows are much developed. The crests for the depressor muscles are extremely strong; they depend beneath the basal margin, and are remarkable (fig. 5 c) from being furnished each with fine sub-crests.

Animal's body, unknown.

7. CHTHAMALUS INTERTEXTUS. Pl. 19, fig. 1 a, 1 b.

Shell, when well preserved, violet-purple: sutures, when not obliterated, formed by oblique interfolding laminæ: basis membranous, but surrounded by a ledge formed by the inflected basal edges of the parietes: scutum and tergum completely calcified together.

Hab.--Philippine Archipelago; Mus. Cuming.

General Appearance and Structure.--Shell depressed, with a large diamond-shaped orifice. Colour beautiful violet-purple, but externally much obscured by disintegration, causing the shell to be ashy gray. Walls smooth or slightly folded. Sutures generally quite, or almost quite obliterated; but when well preserved, they differ remarkably in appearance from those in the foregoing species; for the radii externally here consist of oblique plates or laminæ arising on both sides of the sutures, standing nearly parallel to the parietes, and interfolding with each other. These laminæ are rather plainly marked by lines of growth. Essentially the radii do not differ much from those in C. dentatus and Hembeli; we have but to produce obliquely upwards the transverse and interlocking ribs on their radii, and so convert them into laminæ. During the diametric growth of the shell, the sutural edges of the alæ are added to, in the usual manner, by upturned lines of growth; and, in addition, the recipient furrows of the alæ are similarly added to, so that the lines of growth are upturned, and alæ appear to have been developed on both sides of the sutures in the same way as the radii appear to have been developed on both sides in many Chthamalinæ, though rarely in the Balaninæ. The inside of the shell is beautifully coloured rich violet; it is punctured with small holes as so often is the case with C. stellatus. In every specimen (all full-grown) which I opened, the inner basal edges of the parietes were inflected rectangularly inwards, forming a smooth-edged ledge all round the basal membrane, which, in proportion to the width of this ledge, was by so much reduced in diameter. The largest specimen which I have seen was .35 of an inch in basal diameter.

Opercular valves.--The scuta and terga, in all the specimens which I have seen, were firmly calcified together; in some, a trace of a suture could be seen externally, but hardly a trace internally. In one specimen, there were vestiges of some impressed lines on the scutum, in exactly the same position in which such occur in C. Hembeli. The scutum is rather narrow. The basal margin of the tergum is either straight, or depends a little on the scutal side, thus producing a small spur: the crests for the depressor muscles are strongly marked, and depend beneath the basal margin.

Mouth.--The labrum is strongly toothed: the palpi have long hairs along the exterior basal margin: the mandibles have only three main teeth, and the inferior coarsely pectinated portion is short; the maxillæ deeply notched. Cirri: the first and second pairs have their rami slightly unequal in length; the third pair differs from the same pair in the other species of the genus, in having some few of the basal segments on the anterior ramus thickly clothed with spines, so as to be brush-like: there is even a trace of a similar structure in the lowest segments of the posterior ramus. In the three posterior pairs of cirri the segments are much elongated, and support four pairs of spines.

Branchiæ.--Unknown.

8. CHTHAMALUS SCABROSUS. Pl. 19, fig. 2 a-2 d.

Shell (when well preserved) dull purplish-brown: sutures formed by oblique interfolding though rarely well developed: tergum with a deep narrow pit, at the basi-carinal angle, for the depressor muscle.

Hab.--Peru, Chile, Tierra del Fuego, Falkland Islands. Very common; attached to littoral rocks and shells, and often associated with Balanus flosculus, and sometimes with Chthamalus cirratus; Mus. Brit., Cuming, W. Dunker, Darwin.

General Appearance and Structure.--Shell generally depressed; when growing crowded, sometimes cylindrical: colour dingy purplish-brown, but when much corroded, dirty gray; very young shells are very dark green, owing to the corium, which is of this colour, being seen through the valves. Surface generally rugged, from irregular slight longitudinal folds, and from the transverse overlapping tile-like lines of growth; but sometimes the surface is nearly smooth, with very slight longitudinal folds, these being gray coloured, the intermediate parts being pale dingy purple, the shell thus becoming striped. Orifice rhomboidal, passing into trigonal, owing to the great width of the carinal end. Sutures generally very distinct, rarely obliterated in the cylindrical varieties. Radii narrow, generally exposing much of the alæ, which are plainly marked by lines of growth: the radii themselves, when well developed, which is not often the case, consist of small laminæ or ridges, placed on both sides of the sutures, and interfolded or interlocked together: usually only a trace of this structure is exhibited, but occasionally, along some or along all the sutures (as in the specimen figured), the laminæ of the radii interfold, as plainly as in C. intertextus. The alæ differ slightly from the alæ of the other species, in not forming so much of a rectangular projection, the lower margin running with a gentle curve into the parietes. The internal surface of the parietes is either smooth, or near the basal margin is roughened with depending points: in some specimens from the Falkland Islands, both edges of each suture were inflected, forming a double ridge, with roughened edges, resting on the basal membrane, and supporting the shell. I must mention that in my notes made at these Islands, I remark that the basal membrane seemed sometimes to be surrounded by a calcareous rim; none of the specimens brought home are thus characterised; but bearing in mind the affinity of this species to C. intertextus, no doubt we have here an indication of the shelly ledge surrounding the basis, as described under that species. The largest specimens which I have seen are a quarter of an inch in basal diameter.

The Opercular Valves generally have their summits much worn down. The scuta are elongated in the line of the longer axis of the orifice; the articular ridge is very prominent, and is placed in the middle of the tergal margin. The terga are very narrow, as in some varieties of C. stellatus: they are remarkable in two respects, namely, in the depressor muscle being attached to a plate, formed apparently by the union of the usual crests, parallel to the outer lamina of the valve itself, a deep narrow cavity (fig. 2 d, p) being thus formed; and secondly, in the far more extraordinary circumstance of the existence of a small pit (q) at the extreme basi-scutal corner of the valve, in which about half of the scutal lateral depressor muscle is attached: I have observed no other instance in any cirripede of the partial attachment of a muscle properly belonging to one valve to another valve. The figures of the valves 2 b, 2 c, 2 d, are from specimens most unusually perfect, with the upper portion not worn away; the ordinary appearance of the valves as seen from above, is given in fig. 2 a; at fig. 2 d, a view is given of the tergum seen from vertically beneath, showing the cavity for its own depressor muscle, and for part of the lateral depressor muscle of the scutum.

Mouth.--The crest of the labrum is hairy, without teeth: the palpi have long spines at the end, but none along the inferior margin: the mandibles have either four or five graduated teeth, the lower ones of which are plainly double laterally: the maxillæ have a very sinuous edge. Cirri: the first and second pairs are very short: on the four posterior pairs the segments support either four or five pairs of main spines, with the small intermediate spines rather larger than usual.

Branchiæ.--None; but where they ought to occur, there are two very slight ridges clothed with hairs, about the 1/100th of an inch in length. On the prosoma, there is a slight ridge, extending from the base of the first cirrus towards the adductor scutorum muscle, also clothed with hairs; this unusual character of the prosoma being hairy is common to C. dentatus.

This species is the commonest cirripede on the shores of the Falkland Islands: many of the specimens are there crowded together, and rendered elongated and cylindrical, with the walls very thin, and the sutures often obliterated; as the opercular membrane is very narrow, the opercular valves are much influenced both in their outline and in their crests and articulations, by the varying form of the shell: I have even seen specimens with the scutum and tergum on one side twice as large as on the other side.

13. CHAMÆSIPHO--Nov. Genus.[132] Pl. 19.

[132] Χαμαι [Greek: Chamai], on the ground, and σιφων [Greek: siphôn], a tube.

Compartments four, with the sutures often much obliterated: basis membranous.

Distribution, Australia, China (?). Attached to littoral shells and rocks.

The two species united under this genus agree in having only four compartments, and in these having a strong tendency to become confluent; but they resemble each other hardly in any other respect, more than do all the species of the present sub-family. Chamæsipho columna differs from all the other Chthamalinæ in the structure of its second pair of cirri, and C. scutelliformis differs from all in its shell,--namely, in the small size of the rostrum, with its alæ but little developed, and in the very peculiar apertures in the three other compartments. Hence this genus can hardly be considered a very natural one, though I could not introduce the two present species into Chthamalus, or into any other genus, without doing still more violence to the principles of classification followed throughout this work. Chamæsipho bears nearly the same relation to Chthamalus, as Tetraclita and Elminius do to Balanus.

1. CHAMÆSIPHO COLUMNA. Pl. 19, fig. 3 a-3 c.

LEPAS COLUMNA. Spengler. Skrifter Naturhist. Selbskabet, b. 1, (1790), Tab. 6, fig. 6.

Sutures, excepting during early youth, generally obliterated both externally and internally: tergum with small pits for the attachment of the depressor muscle.

Hab.--New South Wales, Tasmania, New Zealand; extremely common; attached to littoral shells and rocks; often associated with Chthamalus antennatus and Elminius modestus; and in New Zealand, often thickly coating Elminius plicatus.

I have identified, with some doubt, the present species with the Lepas columna of Spengler, obtained from Otaheite, as no description is given by him of the opercular valves, and more especially as Spengler's specimens were an inch in height and seven lines in width, which is much larger than any of the many specimens seen by me: from Spengler's clear description of the structure of his shell, it evidently belongs to the present genus.

General Appearance and Structure of Shell.--The sutures separating the four compartments are generally, excepting at an early age, quite obliterated, both internally and externally, the shell in this case consisting of a single piece, with its summit and opercular valves always much worn. Occasionally the sutures are preserved, and then the four compartments are seen to be of nearly equal sizes. The orifice is always broadly oval, with the carinal end the broadest; and it often approaches closely to circular. The upper part of the shell is frequently steeply conical, with the lower part spreading and folded; sometimes deeply folded. Very young shells are apt to be remarkably smooth. The radii appear never to be developed: the inside of the shell is smooth. The colour is either blackish-green (this being the tint of the corium lining the sack), with the upper part gray from disintegration; or the lower part is brown, from the investing membrane, the shell itself being pale coloured. This species seems particularly liable to grow crowded together; often covering rocks and shells with a honey-combed layer. The basal diameter of some of the largest specimens was .3 of a inch. In Mr. Cuming's collection, however, there is an Australian specimen .55 in diameter and .3 in height, which is, moreover, remarkable from the projecting, extremely rugged, overlapping, dark-coloured layers of growth, which surround the lower part of the shell: we have seen that Spengler's specimens, said to have come from Otaheite, are even broader and considerably higher.

Scuta: from the disintegration which the valves have undergone, the scuta and terga are externally seen to be locked together by a deeply sinuous articulation. The Scuta have a wide articular furrow and a very prominent articular ridge; but the exact outline of these parts varies greatly, very much as in the genus Chthamalus.

The Terga are very narrow, with the under surface channelled: the attachment of the depressor muscle offers the only peculiarity,--the muscle being attached to four or five little pits, placed transversely to the longer axis of the valve; the septa between these little pits evidently answering to the crests as usually developed.

Mouth.--The crest of the labrum is hairy, and slightly bullate. The palpi are rather small, with long spines at their ends. The mandibles have four (sometimes five) teeth, with the inferior portion pectinated. The maxillæ are notched.

Cirri.--The first pair presents no remarkable character. The second and third pairs are subject to extreme variation, as in Chthamalus antennatus and Tetraclita porosa. In all the specimens, the anterior ramus of the second cirrus is short, with all the segments thickly covered with bristles; it is the posterior ramus which varies so much in relative length and in the arrangement of the bristles; but in no case are all the segments clothed with bristles as on the anterior ramus, and as is normally the case with all sessile cirripedes. In some specimens from New Zealand, the anterior ramus having only five segments, the posterior ramus was twice as long, having sixteen segments, with the bristles arranged in circles, but standing rather thicker together on the basal segments. In a Tasmanian specimen, the posterior ramus was only a little longer than the anterior ramus, and the spines were arranged in regular pairs (as on the three posterior pairs of cirri) on all the segments, excepting the few basal ones, on which they were more crowded: a nearly similar arrangement occurred in some other specimens from unknown localities, excepting that the rami were of nearly equal length. In the third cirrus, in all the specimens, the anterior ramus has three or four of its basal segments much broader than the upper segments, and thickly clothed with spines (as is the case with one species of Chthamalus, viz. C. intertextus) all the other segments having regular pairs of spines. The posterior ramus of the third cirrus varies in being either much longer than, or only equal in length to, the anterior ramus; in the former case (in the New Zealand specimen) the spines were arranged in circles, giving an antenniformed structure to the ramus; and in the latter case they were arranged in regular pairs. In Mr. Cuming's great Australian specimen, there was a further peculiarity, in the presence on the posterior cirri of a tuft of intermediate spines between the main pairs; and, in there being on those segments, which are thickly covered with spines, certain very large spines, doubly pectinated, with the pectinations elbowed, closely like the spines met with on the cirri in certain species of Pollicipes. Finally, the segments in the three posterior pairs of cirri support five or six pairs of main spines; the dorsal surfaces of the segment are rough and hairy.

Branchiæ, rudimentary; consisting of a small, simple, tongue-formed fold, projecting about 1/100th of an inch. Ova, 16/2000ths of an inch in length.

2. CHAMÆSIPHO SCUTELLIFORMIS. Pl. 19, fig. 4 a-4 d.

Rostrum very small, elongated, triangular: lateral compartments, each with an aperture, and carina with two similar apertures, all four leading into shelly tubular columns.

Hab.--Attached to Pollicipes mitella, probably from the seas of China; Mus. Brit.

General Appearance.--This very singular shell would not, without some examination, be thought to be a cirripede. From the symmetrical position of the four apertures, with the diamond-shaped orifice in the middle, with the sutures on each side of the rostrum, and from its depressed and circular form, this shell bears some resemblance to the perforated species of Scutella. Shell much depressed, generally nearly circular, with the basal margin highly sinuous and even sometimes almost branched. Surface slightly irregular, marked by fine lines of growth, and covered by brown membrane. Of the four compartments, the Rostrum is very narrow, triangular, and comes up to the orifice almost in a point: it is rather depressed, that is, it lies rather below the level of the other compartments: the straight sutures separating it from the lateral compartments are distinct in the upper part, though always obliterated in old shells in the lower part: these sutures are generally far plainer than those separating the lateral compartment from the carina, which in most cases are obliterated and calcified together, excepting close to the orifice. The alæ of the rostrum are not externally visible, and there are no radii to any of the compartments. The Carina is twice as broad as the rostrum, and is furnished with alæ of the usual shape, which are, to a certain extent, externally visible. The Lateral Compartments are broad, being broader than the carina; they are both penetrated, down to the surface of attachment, by a hole or rather tube,--the two holes standing opposite the rostral end of the operculum: the carina is penetrated by two rather smaller but similar holes. It is these four holes which give to this cirripede its very singular aspect: they are rather smaller than the orifice of the shell; they are oval, with their longer axes placed in the direction of the ray of the circular shell: their manner of formation will be immediately explained. The orifice is neatly diamond-shaped and broad: it is rather small compared with the whole shell, and is closed by the operculum, which is seated near the summit of the shell. Basal diameter of largest specimen 2/10 of an inch; few, however, attained this size, and perfect larvæ were included in much smaller specimens.

Structure of Shell.--The rostrum (fig. 4 c) is remarkable from its small size, and from the plainness of its sutures, in comparison with those separating the other compartments, and this is exactly the reverse of what I should have expected in a compartment tending to become rudimentary. Not only is the rostrum small, but the alæ project to an unusually small degree, and gradually slope away into the lower part of the parietes. These peculiarities are even more strongly marked in very young shells: thus in one of the size of a pin's head, the rostrum consisted of a minute parallelogram, without, as far as I could see, any alæ, and was only one fourth of the size of the carina,--this latter compartment being only half as wide as the lateral compartments. The carina, at this early period, had quite distinct alæ.

The tubular prolongations from the four external holes are of course very conspicuous on the under side of the shell (4 b); and their structure is there plainly seen. In extremely young shells the holes are not present; but very soon, at four points of the circumference, namely, two in the carina and one in each lateral compartment, the basal edge becomes indented, and during growth more and more deeply indented; at last the horns or points of the bays, thus formed in the circumference of the shell, grow inwards and meet, the four indentations being thus converted into four rings or holes; as the shell is added to, at its circumference, these come to stand further and further from the exterior margin; and as the shell at the same time rises above the surface of attachment, the holes are added to at their basal edges, and are thus converted into shelly tubes, generally freely open at the bottom as well as at the top. Sometimes these tubes are closed at the bottom, and this is usually caused by their sides having been added to in a spiral direction. A somewhat sinuous double ridge or fissure, leading from the tubes or holes to the exterior border, can always be perceived on the under side of the shell. Occasionally, though rarely, in very old shells, a second series of holes is formed outside the first four holes, and often a tendency to this may be perceived in the just-mentioned fissures expanding a little at their outer ends, thus forming four new circumferential indentations. The purpose of this peculiar structure, apparently, is to give support to the much depressed and thin shell. In Chthamalus stellatus and scabrosus, we have seen a slight indication of a similar structure, in the formation on the under side of the shell, but confined to the lines of sutures, of obscurely tubular pillars: we have also something analogous in the singular midribs, in Platylepas, causing the membranous basis to be convex. I need only further add, that the parietes, in Chamæsipho, are rather thin, and are composed of translucent shell, punctured for the entrance of tubuli, with the punctures often arranged in straight lines.

Opercular Valves (fig. 4 d).--These are attached by a narrow opercular membrane to the sheath, but little beneath the summit of the shell. The Scuta are considerably arched or convex: the articular ridge is very prominent, and there is a thick strong adductor ridge. The Terga have a short, rather broad, rounded spur, placed very nearly in the middle of the valve: the crests for the tergal depressores are moderately developed, and are simple.

Mouth.--The crest of the labrum is hairy, and is much hollowed out. The palpi are small and narrow, with long bristles at their apices. The mandibles have four or five teeth, with the lower part pectinated. The maxillæ are notched. Of the Cirri, the second pair is short, and all the segments are thickly clothed with bristles. The third pair in the arrangement of the bristles resembles the four posterior pairs. The segments in these pairs are elongated, and support four pairs of main spines.

I was not able to observe any Branchiæ.

14. PACHYLASMA--Nov. Genus.[133] Pl. 19, 20.

[133] Παχυς [Greek: Pachus] thick, and ελασμα [Greek: elasma], a valve.

CHTHAMALUS. Philippi. Enumeratio Mollusc. Siciliæ.

Compartments, when the shell is very young, eight; when mature, either six, or in appearance only four owing to the close union of the lateral compartments: basis calcareous.

Distribution, Mediterranean, and New South Wales; deep water.

The two species here included form a very natural genus, though, as far as the shell alone is concerned, at first sight there is an unusual amount of difference between them. This genus offers an instance of a case, far from uncommon in nature, though so unfortunate for the systematist, in which the most obvious and useful characters of a group are completely masked. When I first examined Pachylasma giganteum,[134] I did not doubt that it was a Balanus; and when I first looked at P. aurantiacum, I thought, from there being in appearance only four compartments, that it was an Elminius; in neither case, from the absence of alæ to the rostrum, did I even suspect that the species belonged to the sub-family of the Chthamalinæ. But when I examined the included animal's body, I found, in both species, the labrum bullate, not notched, with the palpi small, and the mandibles with their lower teeth not laterally double. Again I found in the third pair of cirri only the basal segments thickly clothed with spines; and lastly, there were caudal appendages. Now these characters are pre-eminently those of the Chthamalinæ; in fact, they are those met with in the typical genus Octomeris, with the exception of the presence of caudal appendages, and these occur in Catophragmus,--a genus standing next to Octomeris, and in no other genus of sessile cirripedes. Moreover, if we look to the shell of Pachylasma, the absence of pores in the parietes, or at least of symmetrical longitudinal ribs on their inner surfaces, and the peculiar character of the narrow radii, hardly differing in structure from the parietes, are characters which are rare in the Balaninæ, but universal in the Chthamalinæ. Hence, taking the whole organisation of the two species of Pachylasma, it is certain that they must be ranked amongst the Chthamalinæ, though the leading character of the group, namely, the rostrum being furnished, like the carina, with alæ, here fails. Owing to this conviction, I examined very young individuals of P. giganteum, and in specimens only the 1/100th of an inch in height, I was interested by finding eight separate compartments, with the rostrum having distinct alæ; hence, at this early age, as far as the shell is concerned, this species may be said to be an Octomeris; and we have seen that this likewise holds good with the included animal's body; as the young shell increases in size the minute rostrum and rostro-lateral compartments blend together (Pl. 19, fig. 5 b), without even traces of sutures being left.

[134] Dr. Philippi called this species a Chthamalus; giving this generic name from an examination only of the separated valves in a fossil condition.

With respect to Pachylasma aurantiacum, I have no doubt that at an early age it would possess a perfectly distinct rostrum with alæ; for in the one specimen which I have seen, the compound rostrum is divided by sutures, faintly visible, both externally and internally (Pl. 20, fig. 1 a, 1 b), into three compartments (B, A, B), of which the middle one, or true rostrum, still shows, in the manner in which it underlaps the little rostro-lateral compartments, vestiges of alæ. I may remark, that we have here the same structure as in Chelonobia, formerly described, with the following differences, that here the sutures pass through the outer lamina of the parietes, so that, as seen externally, the separation of the three compartments is much more perfect than in Chelonobia; on the other hand, internally, the separation is less distinct, as the two rudimentary rostro-lateral compartments do not form part of the sheath. Pachylasma aurantiacum is further remarkable, from the two lateral compartments (C, D) on each side, tending to blend together, being only separated by sutures not more distinct, externally, than those separating the compound rostrum, but more distinct internally, for they run up the sheath. From these facts it follows, that this species, viewed outside, without particular care, would be said to consist, like an Elminius or Chamæsipho, of only four compartments; if the sheath alone were looked at, there would be said to be six compartments; but when the walls, especially their basal edges, are carefully examined, either internally or externally, the eight compartments can be plainly distinguished.

With respect to the affinities of this genus, we have seen that both in the included animal's body, and, at an early age, in the shell, it is extremely close to Octomeris: in the presence of caudal appendages, and in the basis being calcareous, we have a clear affinity with Catophragmus; in the two lateral compartments of P. aurantiacum, tending to become blended together, we have some relationship exhibited to Chamæsipho, as is likewise shown in the structure of the second and third pairs of cirri. If the genera of the Chthamalinæ were ranged in a circle, Pachylasma would be the point of contact with the Balaninæ. I must repeat, that it is extremely unfortunate that when the shell alone of P. giganteum is examined, it is hardly possible to separate this genus from Balanus.

1. PACHYLASMA GIGANTEUM. Pl. 19, fig. 5 a-5 d.

CHTHAMALUS GIGANTEUS. Philippi (!). Enum. Mollusc. Siciliæ, 1836.

Shell and operculum dirty white: carino-lateral and lateral compartments furnished with similar alæ.

Hab.--Mediterranean; Sicily; deep water; often attached to the Millepora aspera, and sometimes associated with B. tulipiformis. Fossil in the tertiary beds, near Messina. Mus. Brit., Cuming, Stutchbury, Lyell, Philippi.

I owe to the kindness of Dr. Philippi, authentic specimens of his Chthamalus giganteus, from the tertiary beds of Messina: had this distinguished naturalist seen recent specimens, or a fossil one with all the valves united, he would no doubt have perceived that this species cannot be classed with Chthamalus. I am also indebted to Sir Charles Lyell for some magnificent specimens, which he himself collected near Messina.

General Appearance.--Shell conical, rugged, irregular, with the lines of growth plain; colour dead dirty white. Orifice large, diamond-shaped, narrow towards the carinal end; notched. Radii narrow, barely distinct from the parietes; in the same individual sometimes absent, and sometimes forming a mere ribbon, confined to the lower edge of a compartment. The diametric growth is effected by the alæ, which seen externally are broad, and strongly marked by lines of growth. Basal diameter of largest recent specimen 1.15; height of highest compartment (a carina) 1.4; and width at base of widest rostrum .85 of an inch. Amongst the fossil specimens, height of highest compartment (a carina) 1.8, width of the same one inch; width of widest rostrum 1.1 of a inch. One of these carinæ, a little below the middle point, was actually .3 of an inch in thickness, from which circumstance I have given the generic name of Pachylasma.

Scuta, triangular, but the width varies a little: growth-ridges prominent, sinuous, with a few slight furrows radiating from the apex of the valve. Internally, the articular ridge is not very prominent; nor is there a deep depression for the adductor muscle, and none for the lateral depressor muscles. The upper part of the valve projects freely.

Terga, broad, broader than the scuta: the growth-ridges are prominent, and angularly upturned close along the scutal margin; the carinal half of the valve is smooth, with the faintest traces of longitudinal striæ. A portion of the valve, nearly half of its entire width on the scutal side, is slightly depressed below the general level, and depends slightly beneath the basal margin on the carinal side: this evidently forms the spur. The carinal margin is nearly straight, with the lines of growth upturned along it. Internally, the articular ridge in the upper part is extremely prominent: the crests for the depressor muscles are very prominent, and depend beneath the basal margin like a comb: they extend over nearly half the basal margin, and the muscle, in a corresponding manner, is unusually spread out.

Structure of Shell and Radii: the compartments are attached to each other less strongly than in any other cirripede which I have examined, so that when dried specimens are soaked in spirits of wine they generally fall to pieces with a touch. In full and half-grown specimens the carino-lateral compartments are nearly as broad as the lateral compartments; in very young specimens, about 1/20th of an inch in basal diameter, they are proportionally much narrower. The walls are strong even in young specimens; in old ones they attain a thickness I have scarcely seen equalled except in Chelonobia. Their internal surfaces are smooth, as is the basal internal margin in young specimens, but in old specimens it is roughened with short, blunt ridges and little points. The Radii are often absent; when present they are very narrow, and consist merely of a ribbon-like portion, formed by obliquely upturned layers of growth, more prominent than on the parietes. The Alæ are very largely developed; they are added to, during the diametric growth of the shell, in a regular sweep all the way down to the basal margin, and consequently they do not form a rectangular shoulder as is usual; externally they are plainly marked by lines of growth: they are added to a little above the line of attachment of the opercular membrane; their summits are very oblique. The sheath has its basal edge slightly hollowed out.

Basis, solid, calcareous, very irregular, and of variable thickness.

I have, under the Genus, alluded to the structure of the rostrum: in one shell, the basal diameter of which barely exceeded 1/20th of an inch; the compound rostrum (being 5/200ths of an inch in height), had its basal margin (being 9/200ths of an inch in width) rendered deeply sinuous (see Pl. 19, fig. 5 b) by two indentations, corresponding with and caused by two notches at the top of the valve. These two notches extended down barely 1/100th of an inch (strictly 4/1000ths) from the summit and then disappeared; so that when the shell was under 1/100th of an inch in height, (only one distinct zone of growth having been formed), the now compound rostrum consisted of three separate compartments; and there were eight compartments altogether. Of the above three little compartments, the middle one, or true rostrum, had large alæ, which could be most distinctly seen, extending on both sides, under the little rudimentary rostro-lateral compartments. These latter overlapped the compartments on both sides of them, as in all the Chthamalinæ.

Mouth: labrum bullate, with no central notch; nor is the inner fold of the labrum, forming the supra-œsophageal cavity, thickened, as in Balanus: minute muscles run from this inner fold straight back to the cavity formed by the outer bullate fold: the crest of the labrum is hairy, with a row of the minutest bead-like points or teeth. Palpi, small, broad, placed almost parallel to the sides of the mouth, with their apices not nearly touching each other. Mandibles, with three large nearly equal-sized single teeth; the whole inferior angle strongly pectinated. Maxillæ, small, with a broad, square notch beneath the two or three great upper spines.

Cirri: first pair short, with the rami equal in length. Second pair, with the anterior ramus having broader segments than those of the posterior ramus, and with all the segments, except the few uppermost, thickly covered with spines; the posterior ramus has rather less than half the segments thickly covered. Third pair, very slightly shorter than the sixth pair; anterior ramus with the lower segments, less than half of the whole in number, thickly covered with spines; posterior ramus with only the lowest segments, about one fifth of the entire number, thickly covered; the other segments of these two rami, and the upper segments of the posterior ramus of the second pair, closely resemble in the regular arrangement of their spines in pairs, the three posterior pairs of cirri. The pedicel of the third pair supports numerous, irregularly scattered bristles. The segments of the sixth pair bear four or five pairs of main spines, with a few intermediate spines.

Caudal Appendages.--Multiarticulate, narrow, tapering, situated on each side of the anus: each segment has two little tufts of spines on each side of its upper edge. These appendages are about one third longer than the pedicel of the sixth pair of cirri: in a specimen, in which the rami of the sixth pair had twenty-three segments, the caudal appendages had nineteen segments.

Penis short, hairy, finely-ringed, with no projecting point at its dorsal basis. Branchiæ moderately large, nearly circular, not much plicated.

Fossil Specimens.--With respect to the Sicilian specimens sent me by Dr. Philippi and Sir C. Lyell, I can see no difference whatever from the recent specimens, excepting in their greater size and thickness; it must, however, be borne in mind that I have seen only half-a-dozen recent shells. The one fossil scutum which I have seen is rather broader than is usual with the recent, but I have seen one nearly as broad. This species seems to have been extremely common when the beds at Messina were deposited, and probably it attained a larger size than it does at present. The compartments are always found separated, which is easily understood, by the facility with which, as above stated, recent specimens fall to pieces.

2. PACHYLASMA AURANTIACUM. Pl. 20, fig. 1 a-1 d.

Shell tinged with orange; viewed externally seems formed of only four compartments, owing to the carino-lateral and lateral compartments on each side being separated only by an obscure fissure.

Hab.--New South Wales; apparently from deep water, attached to sandstone.[135]

[135] I am indebted to Mr. Bowerbank for this unique and interesting species, which I have deposited in the British Museum.

General Appearance.--Shell conical, smooth, with a tinge of orange colour; orifice large, deeply notched, sub-triangular. Viewed externally, the compartments in appearance are only four; but on close examination, the lateral compartments are seen to be divided by a very fine fissure into two nearly equal compartments. The rostrum is broad and flat, and when carefully examined, it also is seen to be divided by two fine fissures into three compartments; of these the middle one, or true rostrum, is a very little broader than the rostro-lateral compartment on each side; hence, on careful examination, the shell is found to consist of eight compartments. The carina is much compressed. The radii (in my one specimen) are not developed. The carina, and the two lateral compartments alone, have alæ; for the carino-lateral compartments are too closely joined to the lateral compartments, and the true rostrum is too closely joined to the rostro-lateral compartments, to have their alæ developed. The four alæ which are developed, are very broad, widely exposed, and marked externally by lines of growth. The basal diameter of my one, apparently old specimen, is one inch.

Structure of Shell, &c.--The inner surface (fig. 1 b) of the rather thick parietes is smooth, except close to the base, where it is roughened by a few irregular points. The sheath descends low down, and has its lower edge slightly free. The sutures are much plainer on the internal than on the external surface, and can be here plainly seen to be eight in number. That portion of the carino-lateral compartment, which helps to form the sheath, is narrow, though the whole compartment is of very nearly equal width with the lateral compartment. It is a singular fact, that no portion of the rostro-lateral compartment helps to form the sheath; for the alæ of the lateral compartments, overlap the whole upper part of the rostro-lateral compartments, and abut against the true rostrum. Hence, when the sheath alone is examined, the number of the compartments appears only six. In a section the true rostrum can be seen to underlie the rostro-lateral compartments, and thus exhibits vestiges of alæ. The fact of the rudimentary rostro-lateral compartments not forming a part of the sheath offers a marked difference from Chelonobia, which otherwise has this part of the shell very similarly constructed. The diametric growth of the shell, which seems to be considerable, is effected by the four large alæ of the carina and of the lateral compartment on each side. The sutural edges of the alæ are added to in a regularly inclined line down to the basis. The basis is calcareous, and not very thin.

Both opercular valves (fig. 1 c, 1 d) closely resemble those of the last species.

The Scuta are remarkably narrow and elongated: the external surface is slightly furrowed longitudinally, the prominent lines of growth are much wrinkled. The articular ridge is blunt, and not very prominent. The upper part of the valve is reflexed, and a considerable portion must have projected freely. The Terga are nearly twice as broad as the scuta: the carinal half of the valve is very smooth, and is coloured beautiful reddish-orange. The spur is tolerably distinct. The articular ridge is not very prominent.

The Mouth resembles that of the last species. The mandibles have three sharp teeth, with the inferior part narrow and pectinated with long spines: the edge, also, between the upper main teeth, is pectinated with short spines, which latter often have their summits crenated. The maxillæ are notched; the inferior corner is produced into a small step-formed projection. The outer maxillæ are more pointed than is usual.

The Cirri most closely resemble in every detail those of P. giganteum; I can point out only one slight difference, namely, that the lower segments, in the posterior ramus of the third cirrus, which are thickly clothed with spines, are more numerous in proportion to the upper segments with the spines arranged in regular pairs (being as 4 to 14), than in P. giganteum, in which only one fifth (or 4 to 20) are so clothed.

Caudal Appendages.--These are very small, not being more than one fifth of the length of the pedicel of the sixth cirrus: their segments are indistinct, and they support a very few coarse spines. The rami of the sixth cirrus, in the one specimen, had twenty-five segments, whilst each caudal appendage had only five. Hence the caudal appendages are far less developed than in P. giganteum.

15. Genus--OCTOMERIS. Pl. 20.

OCTOMERIS. G. B. Sowerby. Zoological Journal, vol. 2, p. 244, July, 1825.

Compartments eight: radii with their edges crenated: basis membranous.

Distribution, Cape of Good Hope; Philippine Archipelago.

The two species of this genus differ considerably in external appearance, though not in essential character. Both, as the name expresses, have eight compartments: the carino-lateral pair are rather narrower than the lateral. The basis is membranous. The radii are narrow, and are distinctly crenated on both sides of the sutures with the teeth neatly interlocking; but these teeth can hardly be distinguished in the large, corroded specimens of O. angulosa. The crenated structure of the radii is identical with that described under Chthamalus dentatus and Hembeli; if, indeed, we were to add carino-lateral compartments to the shells of these two species, they would belong to Octomeris. I have seen only a few specimens of either species of Octomeris, and none preserved in spirits; and therefore I know nothing of the anatomy of the softer parts: I was not able to make out distinctly any branchiæ. The cirri differ considerably in the two species, in nearly the same way as in the two species of Chamæsipho. In the structure of the second pair of cirri, and in the tendency of the basal margin of the parietes to form bay-like indentations, Octomeris angulosa shows some special affinity to Chamæsipho scutelliformis. Under Pachylasma, I stated that that genus was closely related to Octomeris; and I have just alluded to the close affinity of the latter to the division of the genus Chthamalus, which has crenated radii.

1. OCTOMERIS ANGULOSA. Pl. 20, fig. 2 a-2 b.

OCTOMERIS ANGULOSA. G. B. Sowerby. Zoological Journal, vol. 2, July, 1825. And Genera of Recent and Fossil Shells, Plate.

---- STUTCHBURII. J. E. Gray. Annals of Philosophy, new series, vol. 10, August, 1825.

---- AUGUBRA (?) Chenu. Illust. Conch., Tab. 4, fig. 2.

Shell dirty white, rugged and massive: alæ thick, with their sutural edges coarsely crenated.

Hab.--Algoa Bay, Cape of Good Hope. Attached to littoral rocks; often associated with Balanus Capensis and Chthamalus dentatus; Mus. Brit., Cuming, Stutchbury, Bowerbank.

General Appearance and Structure of Shell.--Shell extremely rugged, irregular, massive, generally much corroded, steeply conical or even sub-cylindrical: orifice large, broad, rhomboidal, of nearly equal breadth at both ends. Colour dirty white, often slightly tinted yellow from the investing membrane, and from thin layers of punctured membrane alternating with the laminæ of shell. The parietes, in old specimens, have very irregular longitudinal ridges, or rather plates projecting out, sometimes much branched, and generally curved inwards so as to meet each other, thus forming round the basal margin a circle of cylindrical apertures. In old large specimens the radii are not developed, and till the compartments are disarticulated there is no trace of the toothed structure of their sutural edges: in this condition the sutures exist as deep, rugged, narrow fissures. In younger shells, the radii, though narrow, are distinct, and have their surfaces transversely ribbed, and their edges toothed and interlocked with the teeth of the recipient furrow. Some of the specimens present a curiously deceptive resemblance to Elminius plicatus. Basal diameter of largest specimen, one inch and a quarter; height one inch.

The parietes are remarkably thick, but the compartments separate easily: I have, however, seen one instance in which they were partially calcified together. Their internal surfaces are very smooth. The sheath does not descend low. The alæ project rectangularly; they have thick edges, and these are coarsely crenated in transverse lines. Of the radii sufficient has been said.

Scuta (fig. 2 b): these, in all the specimens seen by me but one, have been deeply corroded, and their outline, as in Chthamalus, considerably modified: in the one specimen well preserved, the exterior growth-ridges were extremely prominent. The articular ridge does not project much, nor is the articular furrow very deep. There are more or less distinct crests for the lateral depressor muscles. The Terga are rather narrow, with a small rounded spur, moderately distinct. The tips of the crests for the depressor muscle barely depend beneath the basal margin.

Mouth: labrum considerably bullate, with the crest hairy and furnished with a few most minute teeth. Palpi small, with their tips not nearly touching each other. Mandibles with four teeth, of which the lower ones are laterally double: inferior pectinated portion small. The maxillæ are notched, but their outline differed on opposite sides of the individual examined. Outer maxillæ bilobed on their inner face.

Cirri.--The first pair has the rami unequal in length by about three segments, having six segments on one and nine on the other ramus. In the second pair the anterior ramus is remarkably short and extremely broad; the five segments of which it is composed being thickly covered with bristles, some of which are very coarsely and doubly pectinated: the posterior ramus is nearly twice as long as the anterior ramus, and has eleven segments; of these, excepting the two basal segments which are rather thickly covered with spines, the others resemble in the arrangement of their spines the four posterior pairs of cirri, with the exception that there is a single transverse row of rather long spines along the upper and inner lateral edge of each segment. The segments in all the four posterior pairs of cirri resemble each other in bearing each four pairs of main spines (of which the two lower pairs are short), with a tuft of small intermediate spines.

The penis is remarkable from its very small size and shortness, not being more than once and a half as long as the pedicel of the sixth cirrus.

2. OCTOMERIS BRUNNEA. Pl. 20, fig. 3 a, 3 b.

Shell reddish-brown, depressed, thin, finely furrowed longitudinally: tergum with the basal margin having a slight angular bend.

Hab.--Philippine Archipelago; rare; Mus. Cuming.

General Appearance and Structure.--Shell circular, much depressed; coloured brown, with an orange-red tint; surface regularly and narrowly furrowed in longitudinal lines, the intermediate rounded ridges projecting at the basal margin in finger-like points. The eight compartments, when disarticulated, are of nearly equal sizes; the carino-lateral and rostro-lateral compartments being rather smaller than the others. The radii are neatly toothed; but with the exception of these teeth, which are equally developed on both sides of the sutures, and which closely interlock in the lower part of the shell, but stand a little apart in the upper part, the radii can hardly be said to be developed. The alæ do not form a rectangular shoulder, the lower margin being regularly curved into the parietes; the upper margin is only slightly oblique; the external surface is furrowed by lines of growth. The shell increases a little in diameter, chiefly by the growth of the alæ. The parietes are not very thick, with the inner surface smooth, but with punctures placed in rows for the entrance of the tubuli: the laminæ of shell alternate with layers of yellow finely punctured membrane. Basis formed of thin membrane, in concentric slips. Basal diameter of largest specimen, .6 of an inch.

Scuta broad, with the lines of growth few in number, but extremely prominent, so as to form folds: basal margin with a very slight angular bend: articular ridge not very prominent. Terga, with a narrow slip along the scutal margin, having the lines or folds of growth so prominent as almost to form a series of small transverse pits: the basal margin of this portion forms an angle with the rest of the basal margin: no spur can be said to exist: the crests for the depressor muscle depend a little beneath the basal margin: articular ridge very prominent.

Mouth: labrum and palpi as in the last species. Mandibles with three main teeth, apparently single, of which the lower tooth has its upper edge pectinated: the inferior part of the mandible is pectinated as usual. The maxillæ have two notches, one beneath the two upper large spines, and the other in the middle, separating some thicker and thinner spines.

Cirri: first and second pairs short, with the anterior rami in each longer by about two segments than the posterior rami; all the segments thickly covered with bristles. The third cirrus is much longer than the second cirrus, with the posterior ramus longer than the anterior ramus; on the latter the three basal segments, and on the posterior ramus the two basal segments are thickly covered with bristles; the other segments have bristles arranged as on the three posterior pairs of cirri, namely, each segment has four pairs of main spines, of which the two lower pairs are short.

The unarticulated support, whence the articulated portion of the penis arises, is unusually long, equalling the pedicel of the sixth cirrus.

16. Genus--CATOPHRAGMUS. Pl. 20.

CATOPHRAGMUS. G. B. Sowerby. Genera of Recent and Fossil Shells. Plate.

Interior compartments eight, with several exterior whorls of small supplemental compartments: basis either membranous or calcareous.

Distribution, West Indies and Australia. Attached to littoral shells and rocks.

This genus is very remarkable amongst sessile cirripedes, from the eight normal compartments of the shell being surrounded by several whorls of supplemental compartments or scales: these are arranged symmetrically, and decrease in size but increase in number towards the circumference and basal margin. A well preserved specimen has a very elegant appearance, like certain compound flowers, which when half open are surrounded by imbricated and graduated scales. The Chthamalinæ, in the structure of the mouth and cirri, and to a certain extent in that of the shell, fill up the interval between the Balaninæ and Lepadidæ; and Catophragmus forms, in a very remarkable manner, the transitional link, for it is impossible not to be struck with the resemblance of its shell with the capitulum of Pollicipes. In Pollicipes, at least in certain species, the scuta and terga are articulated together--the carina, rostrum, and three pairs of latera, making altogether eight inner valves, are considerably larger than those in the outer whorls--the arrangement of the latter, their manner of growth and union,--all are as in Catophragmus. If we, in imagination, unite some of the characters found in the different species of Pollicipes, and then make the peduncle so short (and it sometimes is very short in P. mitella) that the valves of the capitulum should touch the surface of attachment, it would be impossible to point out a single external character by which the two genera in these two distinct families could be distinguished: but the more important differences in the arrangement and nature of the muscles which are attached either to the opercular valves or surround the inside of the peduncle, would yet remain.

Although all the valves of the shell, even the eight in the innermost whorl, are very thin, yet from their number in the successive whorls, and from each being concave inwards, so as to form a cavity or tube into which the corium enters, the total thickness of the sides of the shell is very considerable. Both of the species of Catophragmus occurred mingled, in the one case with Tetraclita porosa and in the other with T. purpurascens; now the walls of these shells, we know, are very thick, and are permeated by several rows of pores, occupied by threads of corium; seeing this, we may be permitted to believe, that the several exterior whorls of valves in Catophragmus, between which the corium is prolonged for some way upwards, are of service to the animal, by thickening its shell, in an analogous, but not homologous, manner, as in Tetraclita.

Considering the whole structure, external and internal, of Catophragmus, with the one great exception of the exterior whorls of valves, there is hardly a single generic character by which it can be separated from Octomeris and Pachylasma; indeed, I am not quite sure that it would not have been better to have run these three genera together.

Of the two species, I will first describe C. polymerus, and not the C. imbricatus of Sowerby, inasmuch as I have plenty of excellent specimens of the former, whereas the original specimens of C. imbricatus, in the British Museum, consist of one old and not perfect shell, without the opercular valves or the included animal's body; and the other, though quite perfect, far from mature. As far as these materials allow of minute comparison, the whole shell, with the exception of the basis, and the opercular valves agree very closely in the two species, whereas the included animal's body differs more than is usual in nearly related species;--thus, C. imbricatus has caudal appendages, of which there is no trace in C. polymerus, and I have seen only one other instance in which this organ was absent in one species (Scalpellum villosum) and present in the other species of the same genus. Under these circumstances it will be most convenient first to describe in detail C. polymerus, and then only indicate the points of difference in C. imbricatus.

1. CATOPHRAGMUS POLYMERUS. Pl. 20, fig. 4 a-4 e.

Basis membranous: caudal appendages none.

Hab.--New South Wales (Twofold Bay), Mus. Darwin; Swan River (?), Mus. Cuming. Attached to littoral rocks and shells, and associated with Tetraclita purpurascens, Balanus nigrescens, Chthamalus antennatus, Chamæsipho columna.

General Appearance.--Shell nearly circular, moderately or slightly depressed; colour gray. The eight normal compartments of the inner whorl are two or three times as large as those in the second whorl; the other smaller compartments or scales graduate very regularly in size, to mere beads, at the extreme basal edge, and are arranged symmetrically. The general aspect of the shell depends chiefly on the degree to which the surface has been disintegrated, and differs greatly in the two extreme states. When well preserved, the general appearance is very elegant; the scales are all neatly imbricated; they terminate upwards in points, but with their extreme tips generally broken; from laterally overlapping each other, their external surfaces (as seen, when corroded, in fig. 4 d, or when slightly exposed after the continued growth of their basal margins, in fig. 4 a) become longitudinally keeled, often with a secondary ridge or shoulder on one side; they are, also, crossed by rather conspicuous and regular lines of growth, or more strictly, former lines of union between the several valves: the orifice of the shell in this perfect condition is sub-rhomboidal and notched, and the scuta are united to the terga by nearly straight sutures. On the other hand, when the shell has been considerably corroded, and this seems to be the more common condition, the appearance is not elegant: the scales in the successive whorls are not imbricated, but owing to their upper parts having been worn down, they present a tesselated surface (4 d), with the tesseræ graduated in size, and of a peculiar shape, namely, a rectangle, with a more or less broad square projection on the exterior side, together often with a large square notch on one or both corners, caused by their laterally overlapping each other. Some of the shells are so deeply corroded, that no portion of the original surface is preserved, excepting the lowermost bead-like scales; and the whole shell has so rugged an aspect, that the successive whorls of the worn-down valves might easily be overlooked. In the corroded specimens, the orifice approaches to circular in outline, and is large and nearly entire: the scuta and terga are deeply interlocked together. The largest specimen which I have seen was one inch and a quarter in basal diameter.

Structure of the Shell.--The eight inner normal compartments are not thicker than the outer valves, and are far thinner than in ordinary sessile cirripedes. They are arranged as in Octomeris. The lateral compartments are broader than the rostro-lateral and carino-lateral compartments. The shelly laminæ, of which these compartments and the opercular valves are composed, alternate with yellow membranous layers, exactly as is the case with Octomeris. The lateral edges of the compartments, beneath the alæ, in the six compartments having alæ, bend inwards, especially just above the basis, so that the compartments in their lower parts (fig. 4 c) stand much more separate than is usual. The basal edge of each is irregularly toothed. The sheath presents no particular character. The eight compartments have longitudinal shoulders and ribs on their external surfaces, caused by the lateral overlapping and pressure of the exterior scales. They are also marked by slight, transverse or oblique calcareous ridges, caused by the attachment of the membrane, by which they are united to the smaller compartments or scales outside them. A new line of attachment, and consequently a new ridge is formed, lower and lower down at each period of growth, as the shell is added to at the basis,--in the same manner as new ridges are added to the lower edge of the sheath at each period of growth. The shell, excepting in old worn-down specimens, increases largely by diametric growth: during the diametric growth, the outer scales must be laterally separated a little from each other, and probably they are laterally added to; but there are no distinct lines of suture, or rows of smaller scales, corresponding with the sutures between the eight inner compartments. The alæ do not project much; their edges, as well as the shoulders into which they fit, are generally irregularly crenated: they are added to during diametric growth above the line of attachment of the opercular membrane. There is no appearance of radii; but as the eight inner compartments are added to laterally, and are often crenated, on the edges which correspond with the radii in other Cirripedes, such edges must be considered as radii.

With respect to the scales in the several outer whorls, they resemble each other except in size, and the outermost scales are reduced to mere transversely elongated beads. Their basal edges are concave inwards, being bent like the ridge of a house; hence sub-triangular spaces or tubes, lined by the corium, run up between the scales. When perfectly preserved, the outline of each scale is a much elongated triangle, but usually, from their summits having been worn off, the outline is nearly that of a parallelogram. Their basal edges are dentated, and their upper parts, both on the outside and inside, are marked, where joined to the other compartments, by slight calcareous ridges: outside, there are longitudinal shoulders (Pl. 20, fig. 4 b), caused by the lateral overlapping of the adjoining scales; these are best seen in section in corroded specimens (fig. 4 d): on the inside there are, also, in the upper part, slight medial longitudinal ridges, caused by the sutures, which the scales have covered.

In large old specimens there are ten, or even more, whorls of compartments, but it is scarcely possible to count them with any accuracy. The first whorl consists of the eight large inner compartments, though, homologically, it is doubtful whether the rostro-lateral compartments in any sessile cirripede really belong to the same whorl with the others. The second whorl consists of eight smaller pieces, covering the eight sutures in the first whorl (see the tracing of the basal edges of all the compartments and valves in a very perfect specimen, Pl. 20, fig. 4 c). The third whorl, in large and perfect specimens, consists of twice the number, or sixteen, still smaller scales, corresponding with the sixteen sutures of the second whorl; but sometimes there are less than sixteen pieces, owing to some of the scales being large enough to cover two adjoining sutures as well as the intermediate portion of the compartments of the first whorl. In the fourth whorl, instead of there being, even in the most perfect specimens, twice sixteen, or thirty-two pieces, there are only twenty-four; this being caused by single pieces (placed alternately with two pieces) being broad enough to cover two sutures as well as the intermediate portion of the compartment of the third whorl. In the succeeding whorls this same arrangement seems to be the usual one, so that in the fifth whorl, instead of there being, in the most perfect specimens, twice twenty-four, or forty-eight pieces, that is, twice the number in the last whorl, there are only thirty-six scales, or once and a half as many scales.

The Basis is thin and membranous; it firmly adheres to the surface of attachment.

Scuta, nearly flat: the articular ridge is very prominent, and there is a deep articular furrow both above and below; but the precise outline of the ridge and furrows varies: there is a pit for the adductor muscle, but no crests or marks for the other muscles. The Terga are remarkable from the extreme prominence of the articular ridge and depth of the articular furrow. The basal margin viewed internally seems straight, so that there appears to be no spur; but viewed externally, when the crests for the depressor muscles are seen to depend considerably beneath the true basal margin, a slight, very broad spur may be perceived to exist. These depending crests for the muscles are rather thin, but they extend over half the basal margin of the valve.

Mouth.--The labrum is very bullate, being as long in its longitudinal axis as the rest of the mouth: crest hairy, with some very minute teeth. Palpi truncated, with their apices not nearly touching each other; thickly clothed with spines. Mandibles with three large single teeth, of which the lower one has a single fine tooth at its upper basal edge, showing a tendency to become pectinated; inferior part short, coarsely pectinated. Maxillæ notched, with a slight second notch and slight double prominence in the lower part.

Cirri.--First and second pairs short, with the rami in each unequal in length by about four segments; on both rami in the second cirrus, and in the shorter ramus of the first cirrus, there are some coarsely pectinated spines. All four posterior cirri are alike; the segments bear five pairs of strong spines, with a large intermediate tuft of fine spines: the dorsal tuft is also large, consisting of short thick, and long finer spines. There is no vestige of caudal appendages, though present in the succeeding species.

Branchiæ moderately large, in area equalling the prosoma; surface not plicated.

2. CATOPHRAGMUS IMBRICATUS.

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

Basis calcareous: caudal appendages present.

Hab.--Antigua, West Indies, attached to a Tetraclita porosa.

As stated under the genus, this species is known from two specimens in the British Museum, one of which is full-sized, being three quarters of an inch in diameter, but is destitute of the outermost whorls, of the basis, opercular valves, and animal's body; the other is perfect, but very young, being barely two tenths of an inch in basal diameter. As far as the characters can be made out from these materials, I can perceive no difference from C. polymerus in the shell, excepting that in the small specimen of C. imbricatus, there would appear to exist fewer whorls. The opercular valves are likewise closely similar: in the scuta, however, of the young specimen in the present species, the articular ridge seems to be a little broader, but this is so variable a character that no confidence can be placed in it: these valves, moreover, externally have a broad furrow along the middle, running from the apex to the basal margin, which is not the case with the scutum of C. polymerus; but then I have often seen, in young specimens of Balanus, a similar furrow, which is quite absent in full-grown specimens. When we come to the basis we find a good diagnostic character, for here it is calcareous: it is rather thin, solid, and white; towards the outside it is pitted with small cavities, corresponding with the small teeth on the basal edges of the compartments. The latter adhere firmly to the basis. The central internal surface is covered by an irregular network of imbedded cement-ducts, some of which bifurcate. From the description here given, it will be seen that any figure would have been superfluous, the last species having been so well illustrated.

Mouth.--I can point out no difference, excepting that the palpi are here more oval or less truncated at their ends; and that the lower corner of the maxillæ seems to be more prominent. In the Cirri, the rami of the first and second pairs are nearly equal in length: none of the spines are coarsely pectinated. In the four posterior pairs of cirri, instead of a tuft of small spines on each segment between the pairs of main spines, there are only a few minute intermediate spines: the dorsal tufts are also here smaller, but are, as in the last species, composed of short thick, and longer thinner spines.

Caudal Appendages.--This is the only species of sessile cirripede, with the exception of the two species of Pachylasma, which possesses these organs: they are situated on each side of the anus in the usual position: they are minute, equalling in length only the lower segment of the pedicel of the sixth cirrus: in a specimen in which the rami of the sixth cirrus had eighteen or twenty segments, these appendages consisted of only three tapering segments, supporting a few thick spines.

Branchiæ.--I believe I discovered these, consisting of two minute pouches, placed at the carinal end of the sack: if this observation be correct, this species differs from C. polymerus in the much smaller size of these organs.

REMARKS ON BRONN'S LIST OF FOSSIL BALANINÆ AND CHTHAMALINÆ.

The following species of fossil Balanidæ are given in that most useful work, the 'Enumerator Palæontologicus' in Bronn's 'Gesichte der Natur:' it has appeared to me that a few words on each species, might hereafter save others the trouble of searching through several works.

Tubicinella maxima of Morren, said to have been found in the Chalk: this would have been a wonderful fact, considering that no true sessile cirripede has hitherto been found in this formation, and that it implies the existence of Cetacea at this period; but I have been informed that the fossil in question is not a Cirripede.

Diadema bifidum = Coronula bifida of Bronn, in his 'Italiens Tertiär-Gebilde' (1831), p. 126 (no Plate). Without a much fuller description I can form no judgment on this species.

Diadema vulgare is probably the Coronula barbara, a Crag fossil described by me.

Pyrgoma undata, Michelotti, in 'Bull. Soc. Geolog.' tom. x, p. 141, a mere name without any description: probably it is a synonym of

Pyrgoma sulcatum, Philippi, 'Enum. Mollusc. Siciliæ,' which is a synonym of Pyrgoma Anglicum of the present work; found recent and fossil.

Acasta Montagui is probably the extinct Acasta undulata described by me.

Chthamalus giganteus of Philippi, is the Pachylasma giganteum of this work; found recent and fossil.

Chthamalus stellatus, said by Philippi to be found fossil in Sicily; such may be the case, but the littoral habits of the species do not render it very probable.

Balanus carbonarius of Petzholdt, found in the Carboniferous formation! but I have given my reasons, in my 'Monograph on the Fossil Lepadidæ,' p. 5, for disbelieving that this is a Balanus, or even a Cirripede.

Balanus ostrearum appears to be a mere name by Conrad, published by Morton in his 'Synopsis of the Organic Remains of the Cretaceous Group,' 1834, Appendix, p. 8.

Balanus peregrinus is briefly described and poorly figured, without the opercular valves, by Morton, in his 'Synopsis,' ut supra, p. 72, Pl. 10, fig. 5: this Eocene species apparently resembles the Eocene B. unguiformis of Sowerby, described in this work; but quite indispensable details of structure for identification are not given. Another figure of this shell is given in the 'American Journal of Science' (N. S.), vol. i, Pl. 2, fig. 6.

Balanus circinnatus, communis, and pustula, of Defrance, as well as all the other species named by him, are described so imperfectly, that the descriptions are of no value whatever, every description being applicable to every species: I must add, that the B. communis is not the B. communis of British authors, a name applied to several forms.

Balanus Finchii is briefly described and figured, but without the opercular valves, by Isaac Lea, in his 'Contributions to Geology,' 1833, p. 211, Pl. 6, fig. 222. I do not think that I have seen this species.

Balanus Holgeri, Geinitz, 'Grundriss der Versteinerungen,' tab. ix, fig. 19. No opercular valves are given; this species cannot be even approximately recognised.

Balanus proteus, Conrad, 'Fossil Shells of Miocene Formation of U. States,' p. 77, Pl. 44 (in 'Journal Acad. Nat. Sc.,' Phil., vol. vii, p. 134). I cannot recognise this species; it resembles B. porcatus; but as the radii are rather narrow, and apparently with slightly oblique summits, it may be B. concavus; the opercular valves are not figured.

Balanus sagittata is merely a provisional name without any description, given in a paper on the Crag by S. Woodward, in the 'London and Edin. Philosoph. Magazine, Brewster, Taylor, and Phillips,' vol. vii, July-December, 1835, p. 354.

Balanus sublævis, J. de C. Sowerby, in 'Geolog. Trans.,' 2d series, vol. v, Pl. 25, fig. 3. Plate extremely imperfect; description extremely short and useless; a species from India not to be recognised.

Balanus balanoides; the species thus named by Ranzani, and found by Philippi in Sicily, certainly is not the true Lepas balanoides of Linn., but may be B. amphitrite of this work. In British collections of Crag specimens I have found the B. dolosus (nov. spec.) thus named: I much doubt whether the truly littoral B. balanoides of Linnæus has been found fossil.

B. costatus of Montagu, a synonym of B. sulcatus of Bruguière, and of B. porcatus of this work; found fossil and recent. This species was originally described by Linnæus under the name of Lepas balanus. But the fossil Lepas balanus of Brocchi is a different species; if it be the same with the recent Lepas balanus of Poli, then it is the B. perforatus of the present work. Again, the B. sulcatus of Bronn, in his 'Lethæa Geognostica' (tab. 36, fig. 14), is quite different from the B. sulcatus of Bruguière (i. e., B. porcatus of the present work), as is at once obvious from the oblique summits of the radii. Lastly, B. tesselatus of Sowerby is a synonym of B. porcatus, sulcatus, costatus, and Lepas balanus.

B. punctatus of Montagu is a synonym of Chthamalus stellatus, see remarks on that species: the name of B. punctatus is often applied by British authors to varieties of B. balanoides, see remarks on that species.

B. rugosus of Morris's 'Catalogue' is a synonym of B. crenatus; found recent and fossil.

B. sulcatus of Bruguière, a synonym of B. porcatus; found recent and fossil: see remarks under B. costatus.

B. tintinnabulum of Linn., found recent and fossil; but no trust whatever ought to be placed in the identifications of this species given in several works; thus the Lepas tintinnabulum of Brocchi is distinct. The B. crassus of Sowerby is the true B. tintinnabulum. The B. fasciatus of Dujardin (perhaps only a MS. name) probably is also this species. The B. crispatus is only a variety of B. tintinnabulum.

B. dentiformis, Defrance: see B. circinnatus.

B. ornatus, Münster, 'Beiträge zur Petrifact.,' B. 3, p. 29, tab. vi (1840). No opercular valves or details of structure of the several species of Balanus named by Münster, are given, and consequently none can be recognised with certainty.

B. concavus of Bronn, fully described in this work, with the synonyms given; recent and fossil.

B. crassus of Sowerby, a synonym for B. tintinnabulum.

B. latiradiatus, Münster, probably a synonym of B. tintinnabulum, see remarks under B. ornatus.

B. pectinarius, Bronn ('Italiens Tertiär-Gebilde,' p. 128), does not appear to me fully enough described to be recognised.

B. pictus of Münster, possibly a synonym of B. amphitrite: see remarks under B. ornatus and balanoides.

B. plicarius, Bronn: see remarks under B. pectinarius.

B. porosus of Hausman (according to Münster of Blumenbach). I cannot recognise this species in Münster's 'Beiträge.'

B. pustularis of Lamarck, 'Animaux sans Vertèbres.' Scarcely one of the fossil species of Balanus, described by Lamarck, can be recognised; the descriptions are extremely imperfect. There is a figure of B. pustularis in Münster's 'Beiträge,' which makes me think that this may be a synonym of B. concavus of Bronn.

B. pyramidalis, Münster: see remarks under B. ornatus.

B. rhomboicus, Bronn: see remarks under B. plicarius.

B. squamosus, Defrance: see remarks under B. circinnatus.

B. stellaris, Bronn ('Lethæa Geognostica,' tab. 36, fig. 13). To this species, Lepas stellaris (I presume a misprint for stellata) of Poli, is given as a synonym; but the Lepas stellata of Poli is a Chthamalus, and this certainly is not the case with B. stellaris. I have received two specimens from the Continent named B. stellaris, but they certainly differed from the form so called by Bronn, for in that, the parietes are said to be porose and the radii very narrow: these foreign specimens I have named B. inclusus. A species described by me as B. corrugatus, resembles in external appearance the B. stellaris of Bronn, but it is mere labour in vain to attempt identifying Balani by their external characters.

B. striatus, Defrance: see remarks under B. circinnatus.

B. tertiarius, Risso, 'Hist. Nat. de l'Europe Merid.,' vol. iv. I cannot recognise this species.

B. tesselatus, Sowerby, a synonym of B. porcatus; recent and fossil: see remarks under B. costatus.

B. zonarius, Münster: see remarks under B. ornatus; possibly this is a synonym of B. concavus.

B. amphimorphus, Lamarck: see remarks under B. pustularis.

B. crispatus, var. of B. tintinnabulum.

B. cylindraceus, Lamarck. From Chenu's 'Illust. Conch.,' in which work Lamarck's original specimens are figured; it appears that this is the B. psittacus of South America, where it is also found fossil, but assuredly Lamarck is quite in error when he states that a variety of this species occurs fossil near Turin. Bronn (in his 'Italiens Tertiär-Gebilde,' p. 127) gives as a synonym to the Turin fossil the Lepas tintinnabulum of Brocchi (in the 'Conchologia Fossile Subapennina,' t. 2, p. 597), and this probably is correct; and I have hardly any doubt that the Lepas tintinnabulum of Brocchi is the B. concavus of Bronn described in the present work.

B. perforatus of Bruguière is said by Philippi to be found in Sicily: see remarks under B. tulipa.

B. semiplicatus, Lamarck: see remarks under B. pustularis.

B. tulipa of Müller is the B. Hameri of this work, under which name full information on its geological history has been given. The B. tulipa of Poli and Ranzani is the B. tulipiformis of the present work; and this latter species is said by Philippi to occur fossil in Sicily. But there has been so much confusion in the identification of B. tulipiformis, B. Hameri, and B. tintinnabulum, and likewise of B. perforatus (which by Poli was wrongly considered to be L. balanus, Linn.), that doubts must be entertained about which have been really found, until the Sicilian fossils are all carefully examined.

B. ovularis, Lamarck: see remarks under B. pustularis.

B. Uddevallensis, Linnæus, is probably a synonym of the B. Hameri of this work and the B. tulipa of Müller.

[A few other references may be added to those given by Bronn.]

B. miser, stated by Lamarck to be found fossil: see remarks under B. pustularis.

B. patellaris of Lamarck, is stated by Marcel de Serres to be found fossil with several other species of Balanus; thus named without any description in the 'Annales des Scien. Phys. et Nat. de Lyon,' tom. i, p. 417.

B. virgatus, delphinus, and crispus, are names given by Defrance, with absolutely worthless descriptions.

B. radiatus is too briefly described by Risso ('Hist. Nat. de l'Europe Merid.,' tom. iv, 1826), without a figure, to be recognised; it probably is not the B. radiatus of Spengler, Wood, and other authors.

B. goissopomo, lævis, and radiatus, are mere names without any description, published in a Catalogue by F. Hoeninghaus, in the 'Jahrbuch für Mineral. Geog.,' &c., 1831, p. 155.

B. humilis. Conrad, in the 'American Journal of Science,' vol. ii (N. S.), p. 400, 1846, has given a short description, with a woodcut, of this species, from the upper Eocene of Florida. The opercular valves are not described, and I doubt whether the species could be recognised.

2. Family--VERRUCIDÆ.

Cirripedia without a peduncle: scuta and terga, not furnished with depressor muscles, moveable only on one side, on the other side united immoveably with the rostrum and carina into an asymmetrical shell.

The one genus herein contained differs so considerably from all the others in the Order, in the extraordinary unequal development of the two sides of the shell, that I have instituted a Family for its reception. If compelled to place it in one of the foregoing families, I should with much hesitation rank it in the sub-family Chthamalinæ, rather than amongst the Lepadidæ; for it is destitute of a peduncle, and has a shell, though a very different one from that of any true sessile cirripede. In the interfolding sutures which may be considered as representing radii or alæ, in the basis being divided into concentric slips, and in the whole of the basis being attached to the supporting object, this same line of affinity is clearly manifested. On the other hand, in the general shape, manner of growth, and kind of articulation of the scutum and tergum, there is so close an approach to the Lepadidæ, that had I seen these very important valves separately, I should certainly have concluded that they had come from a Pollicipes, allied to certain Cretacean fossil species, as P. fallax and elegans; it likewise, perhaps, deserves notice, that the upward growth of the rostrum, in Verruca nexa, is a peculiarity found only in the valves of the Lepadidæ. Verruca differs both from the Lepadidæ and Balanidæ in the whole shell or external covering, having no other muscle besides the adductor scutorum. In the characters derived from the animal's body, Verruca approaches both families; but in the absence of branchiæ, and in the great development of the caudal appendages, perhaps it comes rather the nearest to the Lepadidæ. Whatever affinity there is to the Balanidæ, it is much stronger to the sub-family Chthamalinæ than to the Balaninæ; though the non-bullate labrum, in three of the species, and the great dissimilarity of the third cirrus from the three posterior pairs, at first seems to indicate a closer relationship to the Balaninæ; but the labrum is never notched, as in the latter sub-family, and in V. nexa it is bullate, and supports palpi of only small size. The dissimilarity, also, of the third pair of cirri, compared with the posterior pairs, is hardly greater than in Chthamalus intertextus and Chamæsipho columna, members of the Chthamalinæ, though abnormal in this one respect. Perhaps even a special affinity is evinced between certain species of Chthamalus, as C. intertextus, and certain species of Verruca, as V. nexa, namely, in the interfolding sutures and in the very peculiar, inflected basal margin of the walls. Upon the whole, the affinities of the Verrucidæ are complex, and nearly equally divided between the two great families of Balanidæ and Lepadidæ, or sessile and pedunculated cirripedes.

Genus--VERRUCA. Pl. 21.

VERRUCA.[136] Schumacher. Essai d'un Nouveau Syst. Class., 1817.

CLYSIA. Leach. Journal de Physique, tom. 85, July, 1817; Clisia, Leach, Encyclop. Brit. Suppl., vol. 3, 1824; Clitia, G. B. Sowerby, Genera of Recent and Fossil Shells.

CREUSIA. Lamarck. Animaux sans Vertèbres, 1818.

OCHTHOSIA. Ranzani. Memoire di Storia Nat., 1820.

LEPAS ET BALANUS AUCTORUM.

[136] According to Bock, in the 'Naturforscher' of 1778, this term was used by Rumph for a Chelonobia, but as it was before the adoption of the binomial nomenclature, according to the Rules, it may be passed over, and does not interfere with the priority of Schumacher.

Distribution, Northern Europe, Mediterranean, Red Sea, Madeira, West Indies, Tierra del Fuego, Chile, Peru.

The shell in this genus is extremely unsymmetrical, not two of the six pieces of which it is composed quite resembling each other. At first it appeared hopelessly difficult to identify, in a homological sense, these six valves, with those of ordinary cirripedes, but the difficulty soon quite vanished. The operculum consists of two moveable valves on one side, namely, a scutum and tergum, but without any moveable valves on the opposed side: the scutum, though remarkable from being much smaller than the tergum, can be easily recognised by giving attachment to the animal's body and to the adductor scutorum muscle. The four other pieces are articulated together, and form the shell surrounding the sack, in which the animal's body is enclosed: of these, the two against which the moveable scutum and tergum shut, are smaller, differ greatly in shape, and are articulated together in a different manner from the remaining two pieces; from these facts alone there would be a strong presumption that they were of a different nature. The fixed valve, against which the scutum shuts, is either furnished with a remarkably prominent plate (a in fig. 1 c, s′; compare this with s′ in the reversed shell in fig. 1 e), or is hollowed out, as in V. nexa, for the attachment of the adductor scutorum muscle. Thus it is rendered probable that this fixed valve is a modified scutum; but a surface of attachment for one end of the adductor muscle might, perhaps, have been developed on any other valve, or a scutum might have become fused with a lateral valve of the shell; the shell on this latter view being rendered in idea more symmetrical. But when a very young specimen is carefully examined, it is found that the moveable and fixed scutum, the moveable tergum and its opposed valve or fixed tergum, at the first period of calcification, resemble each other quite closely; but that, as each zone of shell is added, the differences become rapidly greater and greater: hence, it may be considered as directly proved, that the two fixed valves (S′ and T′ in all the figures in Pl. 21), which are opposed to the moveable valves of the operculum (S and T), consist of an extraordinarily modified scutum and tergum. It has been shown (p. 129), that at the period of the metamorphosis, the two scuta, the two terga, and the carina of the Lepadidæ, commence their growth, under the form of the so-called "primordial valves," and so differ from all the other valves when such occur: now, in two species of Verruca, I have found closely analogous primordial valves on the apices of both the moveable and fixed scutum and tergum (thus affording strong additional evidence that their nature has been rightly interpreted), and on one of the two remaining valves, namely, that at the posterior or carinal end of the shell. Hence, we may safely infer, that this latter valve, which, though very much more developed on one than on the other side, is so far medial as to curl round and cover the line of opening between the moveable and fixed tergum, is really a carina. The sixth valve differs only very slightly in shape from the carina, and is directly opposed to it; therefore, in accordance with all analogy, it must be the rostrum. Consequently, the shell in Verruca consists of a moveable scutum and tergum, a fixed scutum and tergum, a carina and rostrum, and, as we shall immediately see, a membranous basis--the basis being, as in all sessile cirripedes, the homologue of the peduncle in the Lepadidæ.

The moveable scutum and tergum stand at about right angles with the fixed pair; and as these latter form a part of the wall of the shell, which is always steep on this side, the moveable pair, which close the orifice, are nearly horizontal or parallel to the basis and surface of attachment. Hence, the animal's body, which is attached between the two scuta, but nearest to the moveable scutum, also, lies nearly parallel to the surface of attachment; and I was consequently at first led to suspect that the basal membrane was one side of the shell in a modified condition; but the presence of the prehensile antennæ of the pupa in nearly the middle of this membrane, and the sheet of cement-tissue on its under side, demonstrate that this membrane, though lying on one side of the animal, is the true basis. To make all the parts in Verruca hold the same position as in other cirripedes, relatively to the surface of attachment, we must develope the carina and rostrum equally on both sides of the true longitudinal axis of the shell, and insert the newly-developed portion between the basis and the fixed scutum and tergum, reducing the latter in size, and tilting a little up the moveable scutum and tergum; and by this means the animal's body would be turned, so that its dorso-ventral longitudinal plane would stand at right angles to the basal membrane.

Extraordinarily great as is the difference between the right and left sides of the whole shell, yet in all the species it seems to be entirely a matter of chance whether it be the right scutum and tergum with the right side of the rostrum and carina, or the left scutum and tergum with the left side of the rostrum and carina, which become abnormally developed. Nor does there seem to be any relation between the side of the operculum to be attached, whether right or left, and the nature of the surface of attachment; for I have seen many specimens adhering to perfectly level surfaces, and to quite cylindrical branches of Laminariæ; and in these cases, however the larva might attach itself, there could be nothing to favour the development of one side more than the other. Although the attached scuta and terga are larger than the moveable pair, yet, owing to the small development of the carina and rostrum on the attached side, the upper or unattached side must be considered as the most developed. In this respect, and in the circumstance of either right or left side being modified, we are reminded of the structure of Pœcilasma Kæmpferi (described in my former volume on the Lepadidæ), in which the valves on the side of the capitulum, nearest to the crab's body, to which the specimens were attached, were somewhat less developed than those on the opposite side. I may add, that in ordinary Crustaceans, as I am informed by Professor Bell, the unequal development of the thoracic limbs seems quite capriciously to affect either the left or right side of the body.

General Appearance of the Shell.--The shell is in most cases much depressed and irregularly circular; the side formed by the fixed scutum and tergum is always steeper than the other side: the colour is white or pale brownish, and in V. nexa pale red. The surface is naked. The size is small, rarely exceeding a quarter of an inch in diameter, and the whole shell often appears like a mere scale on the surface of attachment. The most remarkable feature in the external aspect is due to the suture between the rostrum and carina, which is formed by oblique, interlocking plates or folds; as all these plates continue to be added to at their extremities during growth, the upper plates become longer than the lower ones; and the plates on both sides of the suture together form a triangular area, with the broad end uppermost, somewhat like the radius of a sessile cirripede: they act, also, like a radius, for their growth serves to separate these two valves, and so adds to the diameter of the shell. The suture between the rostrum and fixed scutum and that between the carina and fixed tergum are nearly of the same nature, but the former is more conspicuous than the latter; neither are so conspicuous as that between the carina and rostrum: accordingly as the right or left scutum and tergum are moveable, so the suture, second in plainness, (see Pl. 21, fig. 1 a, and 1 d,) is placed to the left or right hand. The fourth suture, between the fixed scutum and tergum, as viewed externally, is straight, and so very obscure that it has been overlooked by some authors, and the shell described as consisting of only three nearly equal pieces, for the fixed scutum and tergum together are about equal in size to the carina or rostrum. The orifice approaches more nearly to an unequal-sided triangle, with the apex broadly truncated, than to any other figure. The operculum fits with remarkable closeness, and is surrounded by a slight rim, formed by the edges of the four other valves.

Moveable Scutum and Tergum.--The scutum (S in 1 b and 5) is narrow and very small, barely equalling half the size of the tergum, and therefore proportionally much smaller than in any other cirripede; in a very young shell, however, (of V. Strömia) less than a pin's head in size, the scutum equalled the tergum in size. The valve is remarkably thick; it is generally depressed down the middle; but in V. nexa this part is longitudinally ribbed. The occludent margin is curved. On the tergal margin there are two articular ridges (with a deepish furrow between them), of which the upper one (′ in S, in fig. 1 b, and 5) extends from the apex about half-way down the valve; and the other, or lower articular ridge (′′ in S), generally runs down nearly to the basal margin: an angle, running from the apex to the basi-tergal corner of the valve, appears like a third articular ridge, but cannot properly be considered such. The above two articular ridges interfold with analogous ones on the scutal margin of the tergum, and so lock the valves together. On the under side (fig. 1 f), the surface is bounded along the occludent margin by a slight rim: there is generally a very slight depression for the adductor muscle; but in V. Spengleri there is a straight, short, sharp (Pl. 21, fig. 2), prominent adductor ridge.

The moveable tergum is broad and rhomboidal. Externally a prominent axial ridge (′′′ in T, in fig. 1 b, &c.), which widens downwards, runs from the apex of the valve to the basal point, and there projecting slightly, causes the scutum to be indented; this indentation on the scutum appears like a third articular ridge, lying beneath (′′), S, in fig. 1 b, &c. Above the lower and axial ridge, on the scutal margin of the tergum, there is a middle articular ridge, which locks in, between the lower (′′) and upper articular ridges (′) of the scutum (S). Again above the middle ridge there is an upper and third articular ridge (′), which is either quite distinct, as in fig. 5, T, or more commonly is formed by the occludent margin of the valve, as in T, fig. 1 b. The broad extremity of this upper articular ridge is often produced into a slight projection, or shoulder, and this always underlies the scutum, of which the under and upper surface is indented or furrowed (see fig. 1 f), in order to receive this shoulder. The upper articular ridge of the scutum (′, S, 1 b) locks in between the upper articular ridge or occludent margin (′, T), and the middle ridge (′′, T) of the tergum.

Hence, altogether, there are three articular ridges on the scutal margin of the tergum, the occludent margin being generally counted as one; whereas, on the tergal margin of the scutum, there are only two ridges, though, as before noticed, an outer indentation, which is developed as a ridge in V. nexa (fig. 5, S), might almost be counted as a third articular ridge.

I may here just remark, that the furrow between the two ridges on the tergal margin of the scutum, resembles the articular furrow in the scutum of the Balanidæ; but it may be doubted whether the resemblance be more than superficial, as this furrow, in the case of Balanidæ, receives the edge itself of the tergum, whereas here it receives only a ridge, proceeding from the apex of the tergum, to a nearly middle point on its scutal margin. Finally, I may add, that the tergum in this genus, in general shape, in growth (presently to be referred to), in the manner in which the upper scutal shoulder is overlapped by the scutum, and in the presence of the axial ridge, presents a very striking resemblance to certain old fossil species of Pollicipes, and to a limited extent to the living species of Lithotrya.

The scutum and tergum being interlocked, move together; they can be firmly shut by the contraction of the long adductor scutorum muscle. Their opening appears partly due to the elasticity of the membranous hinge (representing the opercular membrane), by which they are attached transversely, just beneath the summit of the carina and rostrum. No doubt the protrusion of the cirri effectively aids the act of opening. These valves are not capable (nor, of course, the other valves) of any other movement; for there are no muscles for such movements.

Fixed Scutum and Tergum.--The fixed scutum is larger than the fixed tergum, and therefore has the same proportions as the homologous valves in ordinary cirripedia, but reversed proportions compared with the moveable scutum and tergum. The shape of neither valve can hardly be described. The fixed Scutum (S′ in all the figs.), externally, seems at first to consist of two portions, namely, a curved occludent rim (a), closely resembling the opposed occludent margin (a) of the moveable scutum (S), having in fact undergone very little modification, (as may be best seen in Pl. 21, fig. 1 b); and secondly, of a much modified portion (marked ′′), which resembles in outline and state of surface the rest of the walls of the shell, and may be called the parietal portion. The rostrum (A) curls round the end of the occludent portion, under an edge (b), evidently answering to the basal margin (b) of the moveable scutum, and is simply united to this portion by membrane, but beyond this part, it is articulated to the parietal portion (′′) of the fixed scutum, by oblique interlocking ridges, like those forming the suture between the rostrum and carina. In V. nexa, however, (fig. 5) the rostrum (A) does not curl round any part of the interlocking fixed scutum (S′), but articulates with it by a straight suture. Internally, the fixed scutum (S′ in figs. 1 e, 1 c, of reversed shells) has a surprisingly large, thin adductor plate (m in fig. 1 c, 1 b), with a rounded outline, projecting nearly parallel to the basis or surface of attachment; the adductor scutorum muscle is attached to its upper surface, and consequently the animal's body lies between this plate and the moveable scutum. In the fixed scutum of V. nexa, however, there is a deep pit, instead of a plate, for this muscle.

The fixed Tergum, likewise, consists of two portions--a middle and lower, or parietal portion, and a rim or upper portion; the rim consists of two unequal arms, answering to the two upper margins (not merely the edges) of the rhomboidal moveable tergum; the longer rim (x in T′, see fig. 5) answers to the carinal margin (x) of the moveable tergum, and may be called the carinal rim; and the shorter rim (o and ′ in fig. 5) answers to the occludent margin (o and ′) of the moveable valve, and may be called the occludent rim. The carina curls round the end of the carinal rim, under an edge, z (much foreshortened in T′ in fig. 1 b, and best seen in fig. 5), answering to at least a large part of the basal margin (z) of the moveable tergum, and interlocks, by a serrated suture, with the edge of the parietal portion of the valve. Internally (fig. 1 e, less plain in 1 c) there is a transverse ledge, notched in the middle, and sometimes deeply hollow beneath, running across the valve in about the line of the adductor plate of the fixed scutum: this ledge, in fact, marks and is partly caused by, the line of separation between the central or parietal, much modified, and the scarcely modified, upper or rim portion of the valve. The use of this ledge is apparently to give attachment, as does the under side of the adductor plate of the fixed scutum, to ligamentous fibres, presently to be mentioned, by which the shell is attached to the basal membrane: the carina and rostrum being so much more gently inclined, do not stand in need of a ledge for their attachment.

By comparing the moveable scutum and tergum with the corresponding fixed valves, in all the species, the modification of the latter may be clearly made out to have been effected as follows; and the case appears to me a striking and interesting one. The moveable scutum and tergum lie in the same plane, and are articulated by the means of three ridges on the tergum (including the occludent margin), and by two on the scutum. The fixed scutum and tergum have to be curved, and to be greatly increased in size; and this is brought about, as we shall see, by the large development of a certain small portion of each valve. Comparing first the moveable tergum (T) with the fixed tergum (T′), the umbo of growth matches the umbo of the four margins of the moveable valve, the carinal (x), basal (z), and occludent (o in fig. 5), margins can be identified with certainty in the fixed valve, from their close similarity in shape, their absolute apposition, or correspondence in position. There remains only the scutal or articular margin, with its three articular ridges; of these, the uppermost (′), inasmuch as in most of the species it is hardly distinct from the occludent margin, can, as we have just seen, be clearly identified, and is overlapped, as it normally should be, by the upper tergal corner of the fixed scutum: the second or middle articular ridge, though not so distinct as in the moveable valves, can be plainly recognised (′′), T′, in fig. 1 b, and 5; and it serves its normal function of articulating the two valves together. But when we look in the fixed valve for the third or axial ridge (′′′), we find in its exact place, namely, extending from the umbo to the extreme opposite end of the valve, between the second articular ridge (′′) and the basal margin (z, see fig. 5), only that portion of the valve which I have called the parietal portion; consequently, I do not doubt that this really is the axial ridge largely expanded. So again in comparing the moveable scutum (S) with the fixed scutum (S′); two of the three margins of the former, namely, the occludent (a, see fig. 1 b) and basal (b), can be identified without a doubt in the fixed valve: the third and tergal margin remains; this should have two articular ridges; of these the upper one, still serving its normal function, can be detected in all the species (′ in fig. 1 b), and can be seen pretty plainly (′ fig. 5) in V. nexa: but of the lower and other articular ridge there is no sign,--excepting indeed the whole parietal portion of the valve, which, from holding an exactly homologous position with the lower articular ridge of the moveable valve, I cannot doubt in this ridge expanded and curiously metamorphosed. Hence, in both fixed scutum and tergum, it is the outermost or lowest of the articular ridges which has been modified and expanded, so as to rest on and be fixed to the surface of attachment. It would appear as if it had resulted from one ridge in each of these valves having been thus used up by expansion (so to express myself), that the suture between the fixed scutum and tergum is more simple than any other suture in the whole shell; and it is owing probably to this straightness, and consequent tendency to weakness, that the valves do not grow along this line, and so do not become separated from each other during growth, as on the three other lines of suture. As it actually is, owing to this suture never being separated, it is even stronger than the others; its edges on the inside (fig. 1 c), I may add, are a little inflected or prominent.

Rostrum and Carina: these valves differ from each other, only in the former (A) being rather the largest, and in being more plainly articulated with the fixed scutum, than is the carina (B) with the fixed tergum. Their umbones stand in their normal places, at the two ends of the orifice leading into the sack, that is, facing the dorso-ventral longitudinal plane of the animal; but they are very unequally developed on the two sides, and hence they rise very obliquely from the surface of attachment. Their summits are nearly square, which is caused by the continued growth on both sides of the oblique plates or ridges, by which they are articulated with the adjoining valves. These plates strikingly resemble, as already stated, the radii in certain species of Chthamalus. Without these articulating plates, the outline of the rostrum and carina would have been triangular, with the apex upwards. In V. nexa, in which the walls of the shell are almost perpendicular, the rostrum (A, fig. 5) is very peculiar and patelliformed, with the umbo sub-central: this results from the development of a border at the upper end of the valve. In this same species, the basal edges of the rostrum, carina, fixed scutum and tergum, are rectangularly inflected, so as to form a ledge round the basis, as in the case of some few species of Chthamalus,--the ledge appearing like part of the real basis. During the growth of the shell, the upper internal ends of the carina and rostrum are either rendered solid, or a ledge is formed on the inside across their summits, hollow beneath, like the sheath of the Balanidæ, to which solid or hollow ledge the basal margins of the moveable scutum and tergum are attached by a rim of membrane, forming a hinge.

Direction of Growth: Minute Structure of Valves.--The shell grows downwards all round its basal margin. As far as the diametric growth of its upper part is concerned, there may be said to be only three valves, for the fixed scutum and tergum never become, as already stated, separated; on the three other lines of suture, the valves are added to on both sides; and thus the whole upper part of the shell, and the orifice, increases in diameter. The moveable scutum and tergum grow along their basal margins, and along the margins by which they are articulated together; but the scutum in this latter respect, less than the tergum. The summits of the moveable scutum and tergum, during continued growth, become either worn away, or they project freely; in this latter case, an internal ledge is added round the upper end of the fixed scutum and tergum, so as to keep the orifice accurately closed. In V. nexa the rostrum, with its sub-central umbo, is anomalous, as already stated, owing to a broad upper internal border growing in a direction almost directly opposed to the basal growth of the moveable opercular valves.

In young specimens, on the apices of both scuta and both terga, and on the carina, but not on the rostrum, primordial valves may be distinguished, resembling the valves, so called, which first appear (p. 129, Introduction) after the metamorphosis in, the Lepadidæ. In the Verrucidæ, however, they are calcareous; and the minute transverse cylinders, of which they appear to be composed, stand further apart, causing the surface of the primordial valve to be marked with little separate circles, instead of by hexagons.

The shelly matter of which the valves are composed is translucent: it is remarkably destitute of any investing membrane. The under surface is marked with rows of minute approximate pores, parallel to the lines of growth, into which the corium enters: after a portion of shell has been dissolved in acid, these threads of corium are seen to change, a short distance within, into cylinders of yellow chitine, running obliquely through the substance of the valve. These cylinders are about 1/2000th of an inch in diameter, but in parts they are spindle-shaped and twice as thick: they vary in length, about 1/100th of an inch being the average length: these cylinders at their upper ends suddenly contract into a point, more or less long, or are produced into a very fine tortuous tubulus of chitine, imbedded in the shell: I have seen in no other Cirripedes tubuli of this structure. There are other ordinary tubuli, such as occur in the valves of most Cirripedes, about 1/6000th of an inch in diameter, and which sometimes alternate with the above-described thicker cylinders. There are no external spines. From the number and length of the tubuli of both kinds, the tissue left after the action of acid is singularly complicated.

Basis.--The basal membrane is thin, and is divided, but not very plainly, into concentric slips, marking the successive increments of growth. In the middle of it, in two young specimens, I found with great difficulty the pupal prehensile antennæ: they were of small size, measuring from the extreme edge of the main or second segment to the end of the disc, only 27/6000ths of an inch: the disc appeared narrow (as in Pollicipes and Scalpellum), with a single spine at the proximate end: the ultimate segment, placed as usual at about right angles to the disc, bore two groups of shorter and longer spines, but I could not count how many. The antennæ were enveloped in a mass of cement of a yellow colour, resembling in all its characters the cement of other Cirripedes. In only one case, I believe I saw bifurcating cement-ducts, of extreme tenuity, viz. 1/15,000th of an inch in diameter. The sheet of cement on the whole under side of the basal membrane, not rarely shows a very irregular reticulated structure. For convenience sake, it will be best to defer the discussion on the very anomalous, though slight, powers of excavation which this genus possesses, and which I must attribute to the effects of some substance secreted probably by the cement-organs. I will here only mention, that the specimens which have excavated a depression, are less firmly attached than those, which have not acted on their support; and that, in the former case, the basal membrane, for a considerable space in the middle, becomes quite detached.

Animal's Body.--The body is much flattened and, owing to the little development of one side of the shell, lies parallel to the surface of attachment. The prosoma is but little protuberant. The articulations of the thorax are unusually straight and transverse. The Mouth is also much flattened: it is placed rather distantly from the adductor scutorum muscle, owing to the production of the lower margin of the labrum. The Labrum is not notched, or even hollowed out in the middle, or (excepting in V. nexa) bullate; its crest is surmounted by about eight (more numerous in V. nexa) little teeth, or by some fine bristles. The Palpi are of moderate size, with their tips nearly meeting; they are slightly curved, and have bristles only on their outer sides and extremities: they are apparently capable of being lifted up and down by a muscle attached to them, just outside the rounded swelling on each side of the labrum to which they are articulated: in V. nexa, however, the palpi are very small and narrow, and their tips do not nearly meet. In this genus, therefore, we find the swollen state of the labrum and the size of the palpi--characters generally invariable and of high classificatory importance--variable. The mandibles have three upper main teeth, with two or three minute lower teeth, or, in V. nexa, with the lower part pectinated with small spines: in V. Strömia, I have seen traces of the second tooth being laterally double--a character of some importance. The Maxillæ have a notch under the upper pair of large spines, with the lower part bearing, as usual, a double row of bristles, and forming a large step-formed projection: these organs are furnished with the usual apodeme and muscles. The Outer Maxillæ are prominent, and deeply lobed on their inner surfaces, the two lobes being clothed with bristles.

Cirri.--The first pair are attached, as usual, on each side of the mouth, and stand some way apart from the five posterior pairs. The second and third pairs differ considerably in structure from the three posterior pairs, which are much elongated. The first pair (excepting in V. nexa) is short, with the two rami slightly unequal in length, and with the segments thickly clothed, as usual, with spines. The second pair is remarkable from the posterior ramus being more than twice as long, and containing thrice as many segments, as the anterior ramus, which is barely as long as the shorter ramus of the first pair: the segments in the anterior ramus of the second pair (only five in number in a full-sized specimen) are broader and more protuberant in front, and more thickly clothed with spines (the terminal spines being doubly pectinated), than are the segments on the posterior ramus; on the latter, the uppermost segments have their bristles arranged in front in simple pairs, with the dorsal spines long, the lower segments being more thickly clothed with bristles, owing to the development of lateral rows. The third pair resembles in every respect the second pair, except in being a little longer, and in the bristles on the posterior ramus being less crowded, more resembling the arrangement of those on the posterior cirri. In V. nexa, however, there is not so great an inequality in length or dissimilarity in structure in the two rami of the second cirrus, and only a very slight difference of any kind in the two rami of the third pair. Fourth, fifth, and sixth pairs have numerous elongated segments, bearing four or three pairs of long slender spines in front, with a single minute bristle between each pair, and with two or three slender spines in the dorsal tuft.

There is a considerable amount of variation in the proportional length, and in the number of the segments, of the several cirri in V. Strömia; in some specimens the two rami of the fourth pair were unequal in length; in some, nearly all the cirri on the lower or attached side were shorter than those on the upper side.

Caudal Appendages.--These are of most unusual length, sometimes even exceeding those of Ibla quadrivalvis, which surpasses, in this respect, all other cirripedes. They arise on each side and over the anus. They consist of numerous (sometimes as many as twenty-four), unequal, cylindrical, thin segments, bearing, at their upper ends, a circle of long and very slender spines. They sometimes equal two thirds or even four fifths of the length of the sixth cirrus; but their length, and the number of their segments, (sometimes imperfectly divided), varies much in different specimens of the same species, and sometimes even on opposite sides of the same individual. In some very young shells, as big as a pin's head, the caudal appendages were proportionally extremely short, and consisted of only two or three segments. No muscles enter these organs; and when the animal is taken out of its sack, they project straight out behind, instead of being curled in, like the cirri.

Anatomical Structure.--The animal's body is attached to the two scuta by the adductor scutorum, and by the other usual muscles running towards the mouth, and surrounding the prosoma. The whole external covering or shell has no other muscles; Verruca thus differing from the Balanidæ and Lepadidæ; but the shell is attached all round, near its circumference, to the basal membrane, by a band of very short fibres, appearing like muscles, but really ligamentous, as determined for me by Professor Quekett. Branchiæ are entirely absent. The alimentary canal presents all the usual characters, but in the prosoma is rather abruptly bent back on itself. The orifices of the two olfactory pouches are not at all prominent; they are placed directly under the outer maxillæ, (homologically in their middle segment), just above a small, medial, tongue-like apodeme. The orifices of the acoustic sacks appeared to be in their usual position beneath the basal articulations of the first pair of cirri. The vesiculæ seminales occupy their usual position in the prosoma; they are not much convoluted; they unite before entering the penis. The probosciformed penis is imperfectly ringed; it is thick and short, and tapers much more abruptly than is usual; it supports a few very thin hairs. The ovarian cæca are spread over the basal membrane, at the bottom of the sack; hence they in fact lie almost on one side of the animal: they consist of two main trunks, proceeding out of the animal's body at the rostral end of the sack, which then branch and inosculate. In specimens of V. Strömia collected by Mr. Peach for me, in Cornwall, during the first week of April, there were included two ovigerous lamellæ, placed transversely across the rostral and the carinal end of the sack: the lamellæ were .11 of an inch in length; they appeared loose and not attached, as in the Lepadidæ, to any ovigerous fræna. The ova, in their earliest age, have one end much pointed, and are 8/1000ths of an inch in length; they become blunter and increase a little in size before the larvæ burst forth. The larvæ, both during their earliest stage and after the first moult, have been excellently figured and described[137] by Mr. C. Spence Bate: they present no particular characters distinct from the larvæ of other Cirripedes. I will only further add, that the structure of the prehensile antennæ still adherent to the basal membrane, indicates that the larva in its last stage,--that is the locomotive pupa,--has a normal character.

[137] 'Annals and Mag. of Nat. Hist.,' 1851, Pl. 7, fig. 8-10.

Affinities.--These have been sufficiently discussed under the family; I need here only remark that all the species, with the exception of V. nexa, are intimately allied together.

Range--Habits--Geological History.--The genus Verruca ranges, being represented by four species, from Iceland to Cape Horn. The species that is found in Tierra del Fuego extends up the west coast to Peru. Our northern form, V. Strömia, (if I may trust a specimen in the British Museum, apparently ticketed in an authentic manner), occurs also in the Red Sea; and this is the only locality in the eastern hemisphere whence I have seen this genus. The species seem generally to live in rather deep water: I procured V. lævigata from nineteen fathoms, on the east coast of Patagonia: V. Strömia is found, according to information given me by Professor Forbes, on the British shores, between five and fifty fathoms, and on the steep shore off Mull, in ninety fathoms; but Mr. Thompson assures me that he once saw it adhering to tidal rocks and likewise to some floating bark. Generally the species are attached to living organic bodies, especially shells of Mollusca and of Cirripedes, to Gorgoniæ, and Laminariæ; less frequently to rocks. We shall immediately see that it has slight powers of excavation. This genus is geologically older than any true sessile cirripede or member of the Balanidæ: V. Strömia is found in the Glacial Deposits and in the Red and Coralline Crag of England: another species (in a state not to be identified) occurs in the ancient Tertiary formations of Patagonia; and another in the Chalk of England and Belgium. The fact of this Family ascending to a Secondary epoch accords, in an interesting manner, with its affinities; inasmuch as though in appearance a sessile cirripede, it is almost equally related to the Lepadidæ and Balanidæ, and is more nearly related to the Lepadidæ than to the Balaninæ, or typical members of the Balanidæ: of the latter, none have hitherto been found in any Secondary deposit, whereas the Lepadidæ culminated during the Cretacean period.

Powers of Excavation.

My attention was called to this subject by Mr. Hancock, whose excellent researches on the boring of Mollusca are well known. Verruca Strömia, when attached to shells destitute of an epidermis, excavates, as he informed me, a slight depression, deepest in the middle; but when the epidermis is present no effect whatever is produced. We shall presently see that the central depression is in some degree distinct from that of the circumference. I have since found Mr. Hancock's observations strictly applicable to V. lævigata, V. Spengleri, and to an ancient tertiary species from Patagonia. From having found that the following cirripedes, viz., Lithotrya, Alcippe, and Cryptophialus, all form their deep excavations by mechanical means, and from having read the above-mentioned memoirs by Mr. Hancock on the boring of mollusca, I was strongly impressed with the idea that the action in Verruca would likewise prove mechanical: but from the following facts I have come to the conclusion that the excavation must be due to a solvent, probably poured out from the cement-ducts, which debouch on the under side of the basal membrane.

In the first place, an epidermis, as just stated, perfectly preserves the shells of the various species of mollusca and certain cirripedes, to which I have seen Verruca attached: this is well shown by comparing the effect produced on the same shell in parts covered by the epidermis and in parts whence it has been abraded; or where the shell of the Verruca had fixed itself, whilst very young, within a crack in the epidermis, and had subsequently, by its growth, turned up the edges, and had then acted on the underlying shell; whereas the specimens attached to the sound epidermis had not produced the smallest effect. Again, I have seen an epidermis-covered mussel-shell encrusted by a hard nullipora, on which V. lævigata was attached; and here the calcareous nullipora, under the middle of the basal membrane, was entirely corroded away, whilst the underlying epidermis and the shell beneath it, were not in the least affected. The protection afforded by the epidermis is still more strikingly shown by contrasting shells with very sharp prominent ridges, when thus invested and when naked, to which Verrucæ have been attached: I have given a figure (Pl. 21, fig. 6) of a piece of an invested Venus, from the surface of which a V. Spengleri had been just removed; on the other hand, I have seen a Peruvian Discina in which even sharper ridges, covered by epidermis, were left absolutely untouched, although projecting deeply into the shell of an attached V. lævigata. I have seen several specimens of this latter Verruca (which has the power of corroding naked shell as deeply as its congeners), attached to the membrane-covered variety of Balanus lævis, the shell of which was thus perfectly preserved: now this membrane is little more than the 1/2000th of an inch in thickness; it is not hard, and so brittle that it generally separates with the Verruca, leaving the underlying shell of the B. lævis with its lines of growth glossy and perfect: it appears to me impossible that a membrane so thin and brittle could resist an action, if mechanical, which has worn away from twenty to forty times as great a thickness of hard shell; but the thinnest film of any matter on which acid does not act, as of grease in certain forms of printing, will perfectly preserve the underlying substance, and as I have ascertained by putting on a drop of acid, is the case with this membrane. I have removed several scores of shells of V. Strömia from the stems of Laminariæ, and when the latter were washed and slightly dried, generally not the least effect could be seen, except that the spots where the shell had adhered were glossy from the still adherent basal membrane: yet the stems of Laminariæ are far from hard. In some cases, however, the attachment of the Verruca seemed to have produced a very slight depression on the Laminaria, but this, I think, may be safely attributed to the growth of the surrounding surface; for I have seen exactly the same effect produced by the attachment of the discs of the antennæ of a Lepas, and these discs, with their long spines, could not possibly produce any excavation; nor is Lepas or its pupa in any case a burrowing animal. Again, I have seen a few specimens of Verruca attached to Gorgoniæ, and they had not acted in the least on the horny axis. I have examined numerous specimens of V. Strömia attached to three pieces of slate-rock, and to one piece of red sandstone, all from different localities, and no effect whatever had been produced; yet the slate-rock, especially in one instance, was soft. Mr. Bate, to whom I am indebted for some of these specimens, also informs me that he could discover no impressions on the slate-rocks, whence specimens of the Verruca had been removed. On the other hand, I have had two specimens of limestone, with attached Verrucæ, one coarse and very impure, and the other hard and marble-like; and in both cases there was a distinct central slight cavity, including loose gritty matter. The loose particles evidently resulted from the unequal action either of a solvent or of some mechanical power on the rock, for it is improbable in the highest degree that the shells should have fixed themselves exactly over small collections of loose particles, even if such could possibly have remained on projecting surfaces of sea-washed rocks.

The above facts seem to indicate pretty plainly that the excavation of the support does not depend on its hardness, but on its containing calcareous matter, liable to be acted on by some solvent: but as this view, considering what we know of Lithotrya and of the two other burrowing genera of cirripedes to be hereafter described, appears improbable, I will add a few additional observations. I most carefully examined the shell and basal membrane of Verruca, and likewise the tissues left after the dissolution of the shell in acid, and could detect no structure at all fitted for boring; and what appears more important, there was no apparent difference in the state of the specimens which had and had not excavated a hollow; and this, I think, would certainly have been the case (as in Lithotrya) if the action had been mechanical. It is not easy to ascertain, owing to the small effect at any time produced, at how early an age Verruca begins to act on its support; but I found two sets of specimens only 1/20th of an inch in basal diameter, which had certainly commenced. The ribbed shell, (Pl. 21, fig. 6), especially the middle rib, shows, in a somewhat exaggerated degree, the typical form of the excavation; it may be here seen that the excavation is of the same depth for some little distance from the circumference towards the centre, but that in the middle it suddenly becomes deeper. I have seen several specimens with a central hollow, without any, or with scarcely any, marginal depression, and likewise the reversed case. These several facts show that the central excavation cannot be due to an equable action, prolonged during the whole growth of the shell, having thus affected the middle more than the circumferential parts, for in this case the excavations would have sloped into each other. In specimens which have not at all acted on their support, the whole basal membrane is firmly attached, as in all ordinary cirripedes, to the supporting surface; but in those which have acted, the middle portion of the basal membrane is quite unattached, and the circumferential portion is, I think, less firmly attached than is usual; but between these two portions, there is a circular zone strongly cemented to the supporting surface, and which alone keeps the shell in its place. Now, on the mechanical theory, to account for the circumferential hollow, the basal edges of the shell together with the circumference of the basal membrane must be subjected to movement, but the shell is united to the basal membrane by corium and by transparent structureless chitine (both of which may be left out of question) and by a circle of short fibres, which adhere at their lower ends to the firmly cemented circular zone, and by their upper ends to the shell; and these fibres have been very carefully examined by Professor Quekett, and pronounced to be not muscular, but exclusively ligamentous, and therefore incapable of moving the edge of the shell. The basal membrane over the central hollow is, as stated, quite loose: its lower surface, formed by a reticulated layer of horny cement-tissue, shows no signs of abrasion, and the membrane is so brittle and tender, that in specimens which have been once dried and then well soaked, it almost invariably cracks when the shell is removed, owing to its mere adhesion to the delicate inner tunics of the sack; yet on the mechanical theory, the wearing of the central hollow must have been caused by the action of this middle portion of the basal membrane,[138] which, it may be repeated, is destitute of muscles. From the presence of the prehensile pupal antennæ, enveloped in cement, nearly in the centre of the basal membrane, it is certain that this spot was originally attached to the supporting surface, and has since been detached from it; as, moreover, the central hollow goes on increasing in diameter with the growth of the shell, it is certain that the inner edge of the firmly attached circular zone of basal membrane must likewise continually go on becoming detached: it may, then, be asked by what force can the basal membrane, seeing that it is united to its own shell above only by fibres of ligament near the circumference, be continually torn away from the underlying support, to which it is strongly cemented? On the other hand, on the theory of a solvent slowly poured out from the cement-ducts, its separation from its support is simply explained. It might be supposed that the calcareous matter, when dissolved, would not be able to escape from the central hollow, owing to the basal membrane being so firmly cemented all round it; but the attachment is by a reticulated layer of cement; and I infer that it must be permeated by open passages, from the fact of the hollow being often filled, in dried specimens, by a bubble of air, instead of the basal membrane being pressed closely down into the hollow, as would have been the case had the hollow been hermetically sealed up. I have seen a few instances in which the bottom of the central hollow was occupied, (as was remarked to me by Mr. Hancock), by a little chalky and gritty matter; and in the case of one of the specimens of calcareous rock, before alluded to, by coarse grains and oxide of iron; this seems quite compatible with a solvent acting more readily on certain parts of the rock or shell than on other and less soluble parts or particles.

[138] Mr. Hancock suggests to me that the basal membrane, on the mechanical theory, need not itself move; the motion of epithelial scales, were they transferred into cutting agents, might be supposed to be sufficient. But of such scales, though I used very high powers, I could see no trace; and their presence on the under side of the layer of cement seems hardly possible. Moreover, according to Von Siebold ('Anatomie Comparée,' tom. 1, p. 412), ciliary action has not been observed in any Crustacean, or indeed any Articulate animal. This same statement is likewise made in Annals and Mag. of Nat. Hist. 1854, p. 136, by Dr. T. Williams.

The greatest depth of the central hollow, in any specimen seen by me, even measuring from the top of a rib in the case of a ribbed shell, to the deepest point, was only 1/50th of an inch; but considering how much depressed the shell of Verruca is, I have no doubt that this small gain of space is of service to the animal: we must suppose the loose middle portion of the basal membrane is stretched slightly, or splits and is repaired, so as to fit the hollow. With respect to the even much slighter circumferential excavation, it barely equals in depth the thickness of the extreme edges of the walls; it must, I presume, give strength to the shell when laterally pushed; but it certainly appeared to me that the individuals which had excavated a depression for themselves, could be pried vertically up much more easily than those which had not acted on their support. Finally, we must suppose that the hypothetical solvent is poured out of the cement-ducts at the extreme circumference of the basal membrane, which is almost loose and destitute of cement, so as to slightly corrode outwards and downwards the calcareous support; the action here then stops, and this rim of basal membrane becomes, after a new rim has been formed and as the shell grows outwards, firmly cemented down to the now slightly excavated surface of attachment; but during all the time the solvent goes on acting in the middle, and continues, during the whole growth of the shell, to encroach on and dissolve the supporting surface from under the inner edges of the previously cemented down, circular zone of basal membrane. I have discussed this subject at considerable length, as it appears to me an interesting one. In this case we have the action of ciliæ[139] and of respiratory currents, to which in the case of Mollusca so much has been attributed, entirely eliminated. It is, also, an interesting fact, that within the same Order we should have some Cirripedes boring by simply mechanical means, and others by a chemical solvent.[140]

[139] See the previous note to p. 516.

[140] The solvent may be carbonic acid gas, as suggested by Mr. C. S. Bate in the case of Mollusca ('Report of British Association,' 1849, p. 73), but here, under the basal membrane, we cannot have the respiratory currents, or the ciliary action (see note, supra), as likewise suggested by Mr. Bate.

1. VERRUCA STRÖMIA. Pl. 21, fig. 1 a-1 f.

LEPAS STRÖMIA. O. Müller. Zoolog. Dan. Prod., No. 3025, 1776.

---- ---- Ib. Zoolog. Dan., vol. 3, Tab. 94, 1789.

---- STRIATA. Pennant. British Zoology, vol. 4, Tab. 38, fig. 7, 1777.

DIE WARZENFORMIGE MEEREICHEL. Spengler. Schriften der Berlin. Gesell., 1 B., Tab. 5, fig. 1-3, 1780.

LEPAS VERRUCA. Spengler. Skrifter af Naturhist. Selskabet, 1 B., 1790.

---- ---- ET STRÖMIA. Gmelin. Syst. Nat., 1789.

BALANUS VERRUCA. Bruguière. Encyclop. Meth., 1789; Clisia verrucosa, Deshayes, in Tab.

---- INTERTEXTUS. Pulteney. Catalogue of Shells of Dorsetshire, 1799.

LEPAS STRIATUS. Montagu. Test. Brit., 1803.

---- VERRUCA. Wood's General Conchology, Pl. 9, fig. 5, 1815.

VERRUCA STRÖMII. Schumacher. Essai d'un Nouveau Syst. Class., 1817.

CREUSIA STRÖMIA ET VERRUCA. Lamarck. Animaux sans Vertèbres, 1818.

OCHTHOSIA STROEMIA. Ranzani. Memoire di Storia Nat., 1820.

CLISIA STRIATA. Leach. Encyclop. Brit. Suppl., vol. 3 (sine descript.), 1824.

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

VERRUCA STRÖMII. J. E. Gray. Annals of Philosophy (new series), vol. 10, Aug., 1825.

Moveable scutum, with the lower articular ridge not half as broad as the short upper articular ridge: shell generally ribbed longitudinally.

Var., with the shell not longitudinally ribbed.

Hab.--Shores of Great Britain and Ireland, Shetland Islands; and, according to various authors, Denmark, Iceland, and shores of northern Europe. Red Sea, Brit. Mus. Attached to shells, laminariæ, rocks, crabs, and floating bark, from low tidal mark to fifty or ninety fathoms.

Fossil in Glacial deposits of Scotland, Mus. Lyell; Red Crag (Walton, Essex), Coralline Crag (Sutton), Mus. S. V. Wood.

I have given so full a description of the genus that little remains to be said under the species. Generally the whole shell is covered (independently of the interfolding, oblique, articulating plates) by narrow, longitudinal ridges or folds; and by this character alone the ordinary variety of V. Strömia can be distinguished (as far as I have seen) from all the other species. The shell is white or dirty yellowish-brown. The scutum has the lower articular ridge on its tergal margin very narrow (but somewhat variable in width), appearing like a mere slight shoulder, against which the longitudinal axial ridge of the tergum abuts: it is not half as wide as the short, upper articular ridge. On the under side there is a very slight depression for the adductor scutorum muscle. There is considerable variation in the degree to which the transverse ledge on the under side of the fixed tergum projects, and therefore in the depth of the hollow thus formed. The specimens with the right-side, and those with the left-side opercular valves moveable, are apparently about equally numerous.

The specimen in the British Museum, from the Red Sea, was attached to a Gorgonia, and was in the same box with a Pyrgoma--circumstances favouring the correctness of the locality--but I am much surprised from the general distribution of the species, that V. Strömia should occur in so distant and isolated an area. After careful examination, I can discover no constant difference between the Red Sea and British specimens.

The specimens from the Crag have not their moveable opercular valves, which offer much more important diagnostic characters than the shell; but as far as the latter is concerned, no difference whatever can be perceived from V. Strömia.

2. VERRUCA LÆVIGATA. Pl. 21, fig. 3 a, 3 b.

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

Moveable scutum, with the lower articular ridge broader than the short upper articular ridge; moveable tergum broader than high, with the upper articular ridge produced into a point.

Hab.--Tierra del Fuego; Eastern Patagonia, nineteen fathoms; Chile; Peru; Mus. Brit., Cuming, Stutchbury, Darwin: attached to shells, and often to Balanus lævis and psittacus.

I can point out no difference in the shell between this species and V. Strömia, excepting that its walls seem invariably to be smooth, which is rarely the case with V. Strömia; perhaps also the oblique interfolding articular plates between the several compartments are here more prominent. It appears that specimens with the left side uppermost, and therefore with the left opercular valves moveable, are considerably more common than those with the right valves moveable. The moveable scutum and tergum are articulated together by much more prominent articular ridges than in V. Strömia, and the two valves together are broader in proportion to their height,--the height being measured from the apex to the basal margin. In the scutum the lower articular ridge is considerably broader than the short upper ridge. In the tergum, the basi-carinal corner is more rectangular, and the whole valve is nearly square: owing to the deep furrow receiving the lower articular ridge of the scutum, the axial ridge of the tergum is proportionally narrower but more prominent than in V. Strömia; the uppermost ridge (formed by the occludent margin of the valve) projects, especially when viewed on the under side (fig. 3 b), as a moderately sharp point.

In the mouth, the lower teeth of the mandibles are more distinct than in V. Strömia; the lower part of the edge of the maxilla is very prominent. In the second and third pairs of cirri the terminal spines on the shorter rami are coarsely pectinated; on the sixth pair there are only three pairs of main spines on each segment; but these several points, according to the analogy of other species, I should expect to be variable.

This species is alluded to by Bruguière, in the 'Encyclopédie Méthodique,' but was confounded by him with the V. Strömia of Europe.

3. VERRUCA SPENGLERI. Pl. 21, fig. 2.

Moveable scutum, with a sharp, straight, medial adductor ridge: fixed scutum not larger than the fixed tergum.

Hab.--Madeira, Mus. Lowe; attached to shells.

It would appear that the present species does not attain quite so large a size as the more northern V. Strömia; the walls are not longitudinally ribbed as is usual with this latter species. The proportional sizes of the compartments seem to be somewhat different; the fixed scutum is either equal to or even smaller than the fixed tergum, instead of being larger, as in V. Strömia; but in young individuals the proportions are reversed. In several specimens the fixed scutum and tergum together were larger than the carina. The rounded adductor plate of the fixed scutum is extremely large. The lines of growth, especially on the moveable opercular valves, are rather more plainly crenated than in V. Strömia. In the moveable scutum the lower articular ridge on the tergal margin varies a little in size, and is sometimes larger than in V. Strömia (but never so large as in V. lævigata), and is placed more in the middle of the tergal margin: but by far the most important character by which this species can be distinguished from all the others, is the presence, on the under side of the moveable scutum, of a straight, prominent adductor ridge, which runs up to and even under the apex of the valve, for it is there slightly hollowed out. In the moveable tergum, owing to the medial position of the lower articular ridge of the scutum, the middle of the scutal margin is more hollowed out, and the axial ridge narrower, than in V. Strömia.

In the animal's body the only difference which I could perceive was that the shorter rami of the second and third pairs of cirri were not so short, compared either to the other cirri or to the longer rami of these same cirri. In the second cirrus, in a moderately-sized specimen, the segments were six and thirteen in number in the two rami, and in the third cirrus, seven and fifteen.

Had it not been for the specimen in the British Museum of V. Strömia, from the Red Sea, I should have concluded, from geographical considerations, that V. Spengleri probably was the species found in the Mediterranean, and noticed by Spengler ('Schriften der Berl. Gesell.,' 1 B., 1780), as a small variety of the northern V. Strömia; and likewise that it was the Creusia echinoides of Risso ('Hist. Nat. Product. de l'Europe,' tom. 4, p. 382, 1826), which is certainly a Verruca, but not described with sufficient minuteness to be recognised.

4. VERRUCA NEXA. Pl. 21, fig. 5.

Shell reddish: moveable scutum, with three strongly prominent longitudinal ridges, besides the articular ridges: fixed scutum larger than the carina, with no distinct adductor plate.

Hab.--West Indies, Mus. Brit.; attached to a Gorgonia.

This species differs considerably from all the others in the genus. The shell is brownish-red, tinted yellow: it is not at all depressed like the former species, but the walls are almost perpendicular or even overhang their bases, and the summit of the shell consequently is broad. This form may be in part, but only in part, due to the attachment on the thin branches of the Gorgonia. The umbones of the compartments are remarkably prominent and sharp. Although the parietes are nearly smooth, yet from being so steep, they are little seen, and owing to the very prominent but rounded ribs by which the compartments and opercular valves are articulated together, the whole shell has a strongly ribbed appearance. The diameter of the largest specimen was .2 of an inch.

The rostrum (A, fig. 5) is patelliformed, with the umbo of growth sub-central, but rather above the middle point; hence this valve, differently from the carina, and differently from the rostrum of the other species, grows not only at its basal margin, and on both sides where opposed to the carina and fixed scutum, but also along its upper margin where opposed to the basal edges of the moveable scutum and tergum: owing to the perpendicularity of this valve, the upper part forms a ledge almost parallel to the orifice of the shell. The carina (B) is of unusually small size, being about only half the size of the rostrum, and scarcely exceeding in size the fixed tergum. The fixed scutum (S′) is large, larger even than the carina; it is oblong, and its shape is more simple than in the other species; this is chiefly owing to the rostrum articulating with the whole of that margin (b) which answers to the basal margin of the moveable valve; whereas in the other species (fig. 1 b) it curls beyond this margin, and articulates with the very protuberant, so-called, parietal portion of the valve. Three or four rounded prominent longitudinal ribs, exactly like the homologous ribs on the moveable scutum, run from the apex of the fixed scutum to the basal margin, and their extremities form the teeth by which it articulates, as just stated, with the rostrum. Its upper articular ridge (′) is more prominent, and placed much lower down in the suture between it and the fixed tergum, than in the foregoing species. The ledge (o) by which the orifice is kept neatly closed, is here more distinct than in V. Strömia: this ledge is necessary, as well as in the case of the fixed tergum, owing to the altered shape of the summits of the moveable scutum and tergum, due to their corrosion and to their coming to project freely. But the most remarkable character of the fixed scutum is, that on the under side there is no great adductor plate, but a rounded hollow with its lower edge only slightly prominent; the absence of the adductor plate, which is present in all the other species of the genus, is no doubt due to the under side of this valve being inclined even outwards, and so standing in some degree opposed to the moveable valve; thus affording on its under surface a place for the attachment of the lower end of the adductor scutorum muscle; whereas in the other species this muscle could not possibly have been attached, without the aid of an adductor plate, to the under side of the much depressed and sloping fixed valve. The fixed tergum (T′) is a little more simple in form than the corresponding valve in the other species; the two arms, answering to the occludent and carinal margins of the moveable tergum, are more nearly equal in length: the internal transverse ledge, separating these rims or margins from the parietal portion of the valve, is but little developed.

All four valves forming the shell are remarkable from having, when full-grown, but not whilst young, their basal edges abruptly inflected inwards, thus forming a ledge all round the basal membrane, as in Chthamalus intertextus and Hembeli.

Moveable Scutum.--This is slightly larger in proportion to the tergum than in the foregoing species: it is chiefly remarkable from the presence of three prominent longitudinal ridges on the main part of the valve, like the two articular ridges on the tergal margin; of these latter, the lower one extends down to about the middle of the tergal margin. The moveable tergum is rhomboidal, with the whole carinal portion marked only by lines of growth: it is only remarkable by the upper of the three articular ridges on the scutal margin being unusually distinct from the occludent margin.

With respect to the animal's body, its several peculiarities have already been pointed out under the genus. The labrum is decidedly bullate, triangular in section, with a row of minute bead-like teeth on the crest; the palpi are very narrow and short, and do not nearly touch each other: this variation in the structure of the labrum and in the size of the palpi, is very remarkable, considering how important, in a classificatory point of view, these parts are in all other Cirripedes. In the mandibles there are either two or three main teeth, with the whole lower part of the organ pectinated with sharp spines. Cirri: the first pair is not short; in the individual examined, the two rami had eleven and twelve segments. In the second pair, the shorter ramus was two thirds of the length of the longer ramus, the segments being in number ten and fifteen; in the arrangement of the spines this second pair resembles its homologue in the three other species. In the third pair, the two rami are very nearly equal in length, having sixteen and eighteen segments; and the segments of the anterior ramus are only a little thicker and more thickly clothed with spines than those of the posterior ramus. The remaining cirri and the caudal appendages are as in the other species.

5. VERRUCA PRISCA. Pl. 21, fig. 4.

VERRUCA PRISCA. Bosquet. Monographie des Crustacés fossiles du Terrain Crét. de Limbourg, Tab. 1, fig. 1-6; 1853.

Shell smooth: moveable scutum, with the lower articular ridge somewhat broader than the upper articular ridge.

Fossil--'Système Senonien et Maestrichtien,' Belgium, Mus. Bosquet; in Chalk, Norwich, Mus. J. de C. Sowerby.

M. Bosquet has admirably figured and described the several separated valves belonging to this species, and I owe to his great kindness an examination of some of them. In Mr. J. de C. Sowerby's collection, also, there is a single specimen, attached to a Mollusc, with the four valves of the shell united together, but without the two moveable opercular valves; it cannot be positively asserted that this is the same species with that of M. Bosquet, but such probably is the case. This is the species to which I alluded in the Introduction to my 'Monograph on Fossil Lepadidæ.' It is an interesting species, from being the only known Secondary one, but in itself it is a very poorly characterised form, and I can point out no important character in the shell by which it can be recognised. The rostrum and carina, which are of nearly equal sizes, are locked together by the usual interfolding plates, and likewise to the fixed scutum and tergum; but these latter plates seem to have been less developed in M. Bosquet's specimen than in the English. The fixed scutum has a large adductor plate, which seems to have been chipped in M. Bosquet's specimen; this valve and the fixed tergum in all essential respects resemble the same valves in V. Strömia. The surface of the shell is very smooth.

The moveable scutum has its occludent margin considerably arched: the lower articular ridge is broader than the upper ridge, in which respects it resembles the same valve in V. lævigata, but the whole valve is not so broad as in that species. There is no adductor ridge on the under surface. The moveable tergum has its upper articular ridge narrow, and slightly produced into a point on the scutal margin: in this latter respect this species also resembles V. lævigata, but the whole valve is not so broad in proportion to its height.

3. Family LEPADIDÆ.

Cirripedia having a flexible peduncle, provided with muscles: scuta and terga, when present, not furnished with depressor muscles: other valves, when present, not united into an immoveable ring.

This Family has been fully treated of in my former volume, published by the Ray Society,[141] and I should here only have alluded to its existence, had it not been for the genus Alcippe, which differs in so many important characters from the other members of the Lepadidæ, that formerly I did not even suspect that it could belong to this Family, and therefore deferred its examination. The genus Alcippe was discovered, well described and illustrated, in 1849, by Mr. Hancock; to whose very great kindness I am indebted for permission to dissect and examine his entire stock of this truly remarkable Cirripede. In the classification of the whole class I have not felt so much doubt, as whether I ought to institute a family for the reception of this genus. Alcippe differs from all other Cirripedes (putting on one side for the instant, the males and complemental males of Ibla and Scalpellum) in the very singular fact of being destitute of a rectum and anus;--in the three segments of the thorax, which usually support the second, third, and fourth pairs of cirri, being without any appendages;--in the fifth and sixth pairs of cirri having their inner or posterior rami metamorphosed into very singular roughened cushions or buttons, which apparently serve to triturate the food;--in the caudal appendages being muscular, and being used conjointly with the cirri;--and lastly, in the pupa having a lesser number of segments in its abdomen and caudal appendages than in (as far as I have seen) any other Cirripede. It will be thought that these characters are amply sufficient to justify the placing Alcippe in a separate family, more especially when the close general resemblance in the animal's body in most of the other members of the Balanidæ, Verrucidæ, and Lepadidæ, is borne in mind. On the other hand, the males and complemental males of Scalpellum and Ibla must indisputably be considered as members of the Lepadidæ; yet the male of Scalpellum vulgare and ornatum has no stomach, anus, or mouth, which is a far more abnormal structure than the absence only of the anus in Alcippe: the cirri, also, in these same males, differ from the ordinary cirripedial type decidedly more than in Alcippe. Again, in the male of Ibla, all the cirri, excepting the fifth and sixth pairs, are aborted, and these two pairs are usually only uniramous; here, then, we have a decided resemblance to Alcippe. Hence, if we might assume that the female Alcippe had partially assumed characters confined to the males of the other genera, it would assuredly stand amongst the Lepadidæ. Independently of this comparison with the foregoing males, the affinities of Alcippe are so special to several genera amongst the Lepadidæ, that it seems unnatural to force it out of the position which it well occupies between Ibla and Anelasma, and place it in another family by itself: thus, in being bisexual, and in the general character of its very curious males, Alcippe shows an affinity to Ibla and Scalpellum; and to the former of these genera it is related in several particulars, such as in the body being lodged within the peduncle, and in the structure of the larval antennæ, &c.: to Anelasma and Alepas it is allied in the general character, and to a certain extent in the muscles, of the capitulum; Anelasma, also, has all its cirri to a certain degree rudimentary, and Alepas cornuta has the inner rami of the fifth and sixth pairs of cirri,--namely, the very same rami which are so curiously modified in Alcippe,--small, destitute of muscles, and functionless for their proper purpose: to Anelasma and Lithotrya it is allied in the peculiarity of the lower end of the peduncle becoming elongated by growth, and in being imbedded; and to Lithotrya by its powers of excavation and manner of attachment. Now, I believe it generally holds good that when a form is really distinct from another group, its affinities are general, or only in a slight degree special to the members of that group. Nor, indeed, can it be asserted that Alcippe differs much more, somewhat more it certainly does, from the other genera, than does Anelasma, with its more singular mouth, spineless rudimentary cirri, and fimbriated peduncle; and I have never regretted having included this genus amongst the Lepadidæ. Hence, after much consideration, I have resolved to consider Alcippe as one of the Lepadidæ, though so curiously modified,[142] and having characters confined to the males of the other genera. Perhaps I have been in some degree influenced by the difficulty of finding external characters by which to separate Alcippe as a family from the other Lepadidæ.

[141] The fossil species have been described in a separate Monograph published by the Palæontographical Society. Since its publication, M. Bosquet has produced an excellent memoir, containing descriptions, with the most beautiful illustrations, of several new Cretacean species of Pollicipes and Scalpellum. The memoir is entitled a 'Monographie des Crustacés Fossiles du Terrain Crétacé, du D. de Limbourg.'

[142] Adrien de Jussieu, in his 'Memoir on the Malpighiaceæ,' 'Archives du Museum,' tom. 3, p. 86, when speaking of the characters afforded by the degraded flowers, which in certain genera are borne together with ordinary flowers, makes the following observations bearing on the question here discussed, viz., whether or not to include Alcippe amongst the Lepadidæ. "Ces exemples peut-être aideront à comprendre comment à des genres d'une organisation assez compliquée, viennent quelquefois s'en rattacher d'autres d'une organisation beaucoup trop simple en apparence, membres appauvris et dégradés d'une même famille, qui lui appartiennent sans la représenter; comment le type, s'y présente comme effacé, ne conservant plus pour se laisser reconnaître que quelque trait isolé, mais caractéristique, dont la valeur, essentiellement ordinale, peut être ainsi constatée." Under the point of view, so strongly and admirably insisted on lately by Milne Edwards ('Annales des Sciences Nat.,' 3d series, tom. 17), of describing types without regarding whether the different members blend together on their confines, perhaps Alcippe should be raised to the rank of a Family: I feel quite unable to decide how properly to act.

But we shall presently find, when we come to Cryptophialus, that all the above difficulties, great as they are, are greatly enhanced, for Cryptophialus is certainly allied in a very direct and curious manner (in decided opposition to the remarks just made on special affinities) to Alcippe, and yet in all the more important parts of its organisation, and in its metamorphosis, it differs so fundamentally, that I have felt myself obliged to form not merely a Family, but a distinct Order for its reception.

Genus--ALCIPPE. Pl. 22, 23.

ALCIPPE. Hancock. Annals and Mag. of Nat. Hist., vol. 4, 1849, Pl. 8, 9.

Fem.--Capitulum without valves, with the orifice spinose: peduncle with the basal end added to during growth; its rostral surface depressed and covered by a horny disc: capitulum and peduncle imbedded in a cavity excavated in the shells of molluscs.

Labrum very large, with a row of long hairs on each side: palpi rudimentary: mandible one-toothed: second, third, and fourth cirri absent: fifth and sixth cirri with the posterior ramus represented by a button-like body: caudal appendages four jointed, muscular: anus none.

Males,--several, adhering to the upper end of the horny disc of the female: capitulum naked, transparent, elongated, with a small orifice at the end: peduncle lobed, with the lower end extending far beyond the pupal antennæ: eye, testis, and vesicula seminalis single; probosciformed penis very long: mouth, stomach, thorax, abdomen, and cirri none.

ALCIPPE LAMPAS, Hancock ut suprà.

Hab.--North-eastern shores of England, fifteen to twenty fathoms, imbedded in dead shells of Fusus antiquus and Buccinum undatum (A. Hancock); south-eastern shores, off the Eddystone, Lighthouse (C. S. Bate).

FEMALE. Pl. 22.

I may premise that after the sketch of the leading peculiarities of Alcippe, and after the discussion on its affinities, just given under the Family, I think it would be superfluous to institute a full generic description, separately from the following detailed account of this most anomalous cirripede.

General Appearance.--The whole animal is from .2 to .3 of an inch in length, of a soft texture, colourless or yellowish, and lives concealed in a cavity of its own formation in the shells of certain Gasteropods. This cavity communicates with the water by a narrow fissure-like orifice (Pl. 22, fig. 4), broadest at the posterior end, where the cirri are exserted; narrow, closed, and generally curved at the other (a) end: the two sides of the fissure (b) are commonly bordered by a calcareous inorganic deposit: the walls of the cavity are worn so thin over the peduncle, at the narrow end of the fissure, that the orange-coloured ovaria can generally be seen through the shell of the mollusc, and hence there is here a distinct fan-shaped stain (fig. 3) on the surface. The animal consists of a compressed capitulum, without valves, and of a sort of peduncle depressed on its rostral face, and covered with a broad, oval, thin, horny disc. We must remember that in the Lepadidæ the peduncle does not essentially differ from the capitulum, being only the flexible lower or anterior end of the animal, and is separated from the capitulum only by shape, and generally by the direction of the lines of growth. The disc, when most regular (fig. 1, H), lies in a plane at right angles to the sides of the capitulum, and almost in a line with the orifice leading into the sack; but the peduncle is often very irregular (fig. 2), and the disc comes even to occupy a position nearly parallel to one or the other side of the capitulum. On the carinal side, the capitulum is generally separated from the peduncle by a rather deep fold (f, in the section fig. 5), but this depends in some degree upon the state of distension of the mass of ovarian cæca. I have given a drawing, fig. 1 (partly taken from Mr. Hancock), of a very regular individual, and of an extremely distorted specimen (fig. 2). The distortion, I believe, is generally caused by the animal, during its excavation, breaking into some old cavity.

External Structure.--The orifice leading into the sack is about one third of the total length of the animal: its edges or lips are thickened, horny, and brownish: at the lower end, exactly where the orifice ends, the lips are formed, from being deeply notched, into two sharp projections (a, figs. 1, 5, 6), unlike anything occurring in any other Cirripede. The external membrane (c, fig. 6) of the lip supports an irregular but nearly straight band of sharp, thick spines of chitine, about 1/1000th of an inch in length, together with a few hairs: at the carinal or upper end of the orifice the spines are largest and most numerous; at the other and lower end, they decrease in size; and on the two projections (a, fig. 6), and on the adjoining parts of the external membrane, they graduate into the small dentated points which cover the whole surface of the animal. The inner tunic of the sack (b), on each side along the upper half of the orifice, is remarkable from having a moderately broad, curved band of short, sharp spines, not quite so thick as those on the external surface, closely adpressed together and pointing upwards, like the javelins of an ancient phalanx, thus probably preventing the ingress of any intruding animal. This band of spines curves at the upper end, conformably with the shape of the orifice. The inner tunic of the sack in this upper part is yellowish, and, what is very unusual, is thicker than the external membrane. A little way down, within the orifice, and more especially in front of an elegant row of hairs on the two sides of the great labrum, there is a band of very fine but stiff hairs (5/1000ths of an inch in length), pointing upwards, and making together with those on the labrum a hedge, barring ingress into the sack.

The external membrane over the whole animal, excepting the horny disc which covers the rostral face of the peduncle, is very thin and transparent; it is periodically and often moulted, as may be inferred from the many old lines of junction round the edges of the horny disc: it is irregularly and pretty thickly (but not so thickly as in fig. 7) studded with star-headed, minute points, from 2 to 5/10,000ths of an inch in diameter, composed of hard chitine, seated on a short footstall, and this on a circular, yellowish, slightly thickened disc of the general investing membrane, appearing like a halo surrounding each little point. These points are directed obliquely upwards. There are none on the horny disc, though particularly numerous close to its margin. Their state varies much: just after a moult, when newly formed, the spines are regularly star-headed, with quite sharp rays, from two to six in number, with some of them occasionally bifid; but these points or rays soon become blunted, and ultimately half the star is worn away, so that the appearance then presented is that of a crescent with a few blunt points on its convex side. At each exuviation, the thickened membrane of the orifice with its strong external spines (the condition of which also varies according to the period elapsed since the last moult), and of course the whole internal tunic of the sack, with its spines and hairs, are all moulted, together with the external membrane and the little star-shaped points. In most specimens a barely distinguishable band or bar of yellowish, slightly thickened membrane, runs from the points (a), at the lower end of the orifice, for some way obliquely downwards; and at the lower end of this bar the weak adductor scutorum muscle (having transverse striæ) is attached. This bar is often strengthened by a prominent external fold of membrane, but yet it is so flexible, and as it is united only to the lower end of the orifice, I can hardly believe that it can, by means of the adductor muscle attached to its opposite extremity, have much power in closing the orifice. I believe that this muscle acts simply in narrowing the whole animal, so as to favour its movement within the cavity in which it is imbedded. Owing to this position of the adductor muscle, and its consequent little power in closing the orifice, we can understand the necessity for the defence afforded by the bands of spines and hairs on the inner tunic of the sack and on the labrum, which do not occur in other Cirripedes.

Horny disc.--The general shape of the disc, its irregularity and position, have been already described. It never extends, as remarked by Mr. Hancock, to the extreme lower point of the peduncle; upwards it reaches to a little below the lower end of the orifice. It consists of successive layers of membrane, either moderately thick and opaque, or only a little thicker than the general membrane of the body, but never furnished with the little sharp points; it increases in size, in like manner as the calcareous valves of other Cirripedes, the undermost and last formed layer extending beyond the others, with its edge united, till the next exuviation, to the general membrane of the body. The disc is attached, at its upper end, apparently in the usual way, by cement, to the roof of the cavity of the shell in which it is imbedded; but the lower parts of the disc are also slightly and partially attached, chiefly along the lines of growth or exuviation; and this, I suspect, is effected by an inorganic calcareous deposit; anyhow I could not perceive here any cement or cement-ducts. Beyond the circumference of the disc the whole animal lies free in its cavity. The lines of growth in the middle part of the disc are generally obliterated by the decay of the older and outer layers. These lines, though of course ordinarily conformable with the general outline of the disc, are not always so, for the disc sometimes becomes during growth slightly changed in form, and the animal, consequently, slightly changed in position; sometimes either one or the other side or the upper end of the disc is left deserted by the new layers of the growing disc; these being formed on the deserted side of less size or extension, instead of larger size, as they normally should be all round the disc.

The upper end of the disc is always produced into a projection of not regular shape, but generally hollowed out or embayed in front (fig. 1), and almost always hollowed out on the two sides. This projection stands directly over the adductor muscle (b in fig. 5), and on the exterior surface is generally convex, being concave on the under side for the attachment of several muscles presently to be described. The horny layers are in this part usually thicker than elsewhere. The disc is thus upwardly produced, owing apparently to the fissure which leads into the cavity of the shell of the mollusc becoming, during the process of excavation, considerably longer than is necessary,--that is longer than the orifice leading into the sack; and consequently, for the protection of the imbedded animal, the lower and narrow end of the fissure is closed on its under side by this upward production of the horny disc, formed of layers of membrane of unusual thickness. A deposition, also, of lime, hereafter to be mentioned, gives further protection.

In the bays on each side of the upward production of the horny disc, and likewise a little lower down on its edges, and therefore somewhat protected by lying within the narrow, pointed, lower end of the fissure in the shell of the mollusc, the short-lived Males (Pl. 22, fig. 1, m) are attached often in groups of two, three, or more together.

It may be asked to what part, in other Cirripedes, does the horny disc answer? Not considering the upward prolongation, which has been developed for a special purpose, the disc is irregularly circular,--is added to all round,--serves for the attachment of the whole animal to the supporting surface,--is covered on the under surface by a conformable and parallel mass of ovarian cæca, and the latter by the inner tunic of the sack; therefore in every character, and in its relation to the other parts of the animal, the disc answers to the end of the peduncle, or to the basal cup in Lithotrya, or still more closely to the basis in sessile cirripedes, with the important exception that it lies in a line with the longitudinal axis of the whole animal instead of at right angles to this axis. We know that all ordinary cirripedes become first permanently attached in their pupal state by their antennæ, which are seated on the ventral or rostral surface, near to the anterior end of the body; and that from the young cirripede, after the act of metamorphosis, being turned vertically upwards, and from the extreme anterior, now lower, end of the body not being rapidly developed, the surface cemented down, or the basis, encroaches almost equally on the dorsal, lateral, and ventral surfaces. But if we were to suppose the extreme anterior point of the body to be rapidly developed, the surface of attachment or basis, without it grew still more rapidly, could not possibly reach the dorsal surface, and would, consequently, be confined to the ventral or rostral surface. I have not seen the young of the ordinary or female Alcippe soon after its metamorphosis, but in the male the development of the extreme anterior end of the body is extraordinarily rapid, and from analogy we may fairly conclude that this is likewise the case with the female. Hence I believe that the horny disc answers to the cemented down, lower end of the peduncle, in other members of the Lepadidæ, and to the basis in the Balanidæ, and that it is confined to the ventral or rostral surface, owing to the anterior or lower end of the body having been rapidly developed. To make all the parts, internal and external, of Alcippe, correspond with those of other cirripedes, the main circular part of the horny disc must be turned up at nearly right angles to its present position (the dorsal or carinal integuments, to the right-hand in fig. 5, being shortened), and then we should have a peduncle, certainly very short and broad, but holding its proper relative position.[143]

[143] In the genus Lithotrya, as long as the animal continues to bore into the rock, the calcareous discs by which it is attached in its cavity, stand, as in Alcippe (Pl. 8, fig. 2, 2_a′_, Darwin's 'Monograph on the Lepadidæ'), parallel to the longitudinal axis, but as soon as the animal ceases to bore, and the discs become converted into a cup, they occupy a normal position at right angles to the peduncle. According to Reinhardt, these discs, in Lithotrya, are situated on the carinal or dorsal surface of the peduncle, at which statement I now feel considerable surprise, as undoubtedly the pupa must first permanently attach itself by its prehensile antennæ on its ventral or rostral surface. In Anelasma I failed to discover any cement or cement-ducts; but I am now strongly inclined to believe, considering that the extreme lower or anterior end goes on growing, that the surface of attachment will be found to occur, as in Alcippe, on the rostral surface, a little way below the orifice.

Sack and its Muscles.--I have already described the curious phalanx of spines, the long fine hairs, and thickened condition of the inner tunic of the sack along the sides of the orifice. This inner tunic is a reflexion from that enveloping the body of the animal, in the usual manner, as may be seen in the section (Pl. 22, fig. 5). Between the external membrane and the inner tunic of the sack (e), there is of course the usual double fold of corium, these two folds being united by minute, transverse, ligamentous fibres, branched at the two ends, as in other Lepadidæ. Imbedded in the corium there are numerous, longitudinal, striæ-less muscles, which do not run quite up to the orifice, but to an oblique line beneath it. Externally to these muscles there are, as in the other Lepadidæ, fine transverse muscles, confined to the middle part of the animal, and running from the carinal margin more than half way round both sides. Attached to the upper notched or folded end of the orifice (g, fig. 5, above the upper ends of the longitudinal muscles), there is a fan of rather strong, striæ-less muscles, expanding downwards, with their lower extremities attached to the outer membrane of the capitulum; these muscles apparently serve to open the orifice: there is a somewhat analogous muscle in Lithotrya, but in no other member of the Family: in Cryptophialus, however, there is a closely similar muscle. Owing to the action of these several muscles, the tissues forming the capitulum and peduncle are, according to Mr. Hancock, highly contractile.

I have stated that the under surface of the upper produced end of the horny disc is concave, and serves for the attachment of several muscles. Of these some run to the basal margin of the great labrum, and no doubt, as usual, move the whole mouth; others, as usual, run to the skin between the labrum and the lower end of the orifice,--i. e. in fig. 5, between the lower end of the row of fine hairs (see fig. 11), which shows where the basal margin of the labrum is situated, and the lower side of the point (a), where the orifice terminates: others run obliquely on both sides towards the point of attachment of the small adductor scutorum muscle (b, fig. 5): others, of considerable strength, and these are more peculiar, run and are attached to the lower end of the orifice (a), and serve apparently to draw up the orifice from within the fissure-like cavity, in which it lies lodged: others, again, extend transversely on both sides, close beneath the inner tunic of the sack, a little beyond the line whence the ovigerous fræna or branchiæ arise. These transverse muscles lie within the longitudinal muscles, and therefore are quite different from the exterior transverse muscles, which are situated more towards the carinal portion of the peduncle and capitulum, and which are common to most Lepadidæ. The internal transverse muscles, and those running to the lower end of the orifice, are peculiar, but we shall hereafter meet with them even more developed in Cryptophialus.

Along the medial carinal line there is, between the two layers of corium, the usual circulatory channel. On each side of this line, on the inside of the sack, there are generally some slight irregular swellings, and sometimes a large extent of the inner surface is irregularly carunculated with little knobs. The sack (e in fig. 5) extends down almost to the basal point of the peduncle (d), more especially when the ovarian cæca are not gorged with ova.

Branchiæ, or ovigerous Fræna.--Within the sack, on each side of the body, rising not far from the ends of the adductor muscle (b), there is a large fillet or fold; the two occupy so exactly the position of the ovigerous fræna that I cannot doubt such is their nature, though, as happens in the case of some species of Pollicipes, they are destitute of their proper glands, and so do not serve for the attachment of the ovigerous lamellæ; this attachment probably is not required, owing to the protected situation which the lamellæ hold in the sack, under the animal's body, and over the ovarian cæca. From the unusually large size of these so-called fræna, I cannot doubt that they serve as branchiæ, equally well with the plicated folds of membrane, believed to be homologous with the fræna, in the Balanidæ, which have by every one been considered as branchiæ. The fræna are broad and truncated at their upper ends; their margins are sinuous, and their outer surfaces papillose; they run longitudinally down the sack, narrowing as they extend, almost to the basal point of the peduncle, and hence are of considerable length; they are hidden in the section (fig. 5) by the medial, somewhat protuberant mass (c) of ovarian cæca, and partly by the (i) prosoma.

Body.--The body is constructed on the usual type, and indeed does not differ greatly from that of Ibla. The labrum is very large, its lower or basal margin is separated by an unusual space (capable of being contracted or folded) from the lower end of the orifice of the sack; hence the labrum and whole mouth is placed quite remarkably near the upper (or carinal) end of the orifice. This upper end of the orifice, I may remind the reader, is homologically the posterior end of the general covering or carapace, and all that portion of the whole animal (as the sectional figure, 5, stands) below the lower margin of the labrum, on the rostral or ventral surface, is formed by the three anterior segments of the head. The main part of the body, carrying the mouth, is formed by the great development of that segment of the thorax which bears the first pair of cirri (h), here closely adpressed, as usual, to the sides of the mouth. The lower portion of this segment forms the prosoma (i), and has the characteristic outline, but is not much developed. On each side of the prosoma an oval space of membrane is yellowish and is thickened, and so gives support to this part of the body. The five succeeding thoracic segments, which ought to carry the five succeeding and posterior pairs of cirri, are together of very small size (as in Ibla), in comparison with either the prosoma, or the whole anterior part of the animal. The segment (k) which should have borne the second pair of cirri, is considerably longer than the following segments, and is at the same time less distinct, owing to an oval convex shield of thickened membrane on the sides, not extending the whole length of the segment, thus causing two transverse creases, which, when the thorax is contracted, appear like two additional segments. Had this segment borne cirri, they would have stood, as in Ibla, at a considerable distance from the first pair. The segments (l, m) which should have borne the third and fourth pairs of cirri are like each other, except that the former is rather the longest. The membrane covering all the thorax is surprisingly thin; and at the articulations, which are straight and transverse, is deeply folded, so that the thorax must be highly extensible, to a degree which I have not seen equalled in any Cirripede except in the males of Scalpellum vulgare and ornatum. The thorax is represented as somewhat extended in fig. 5. This part of the thorax is amply furnished with striated and striæ-less muscles for its retraction and protrusion, and for lateral movements. The segment (m) which should have borne the fourth pair of cirri, at first sight falsely appears like the terminal segment of the thorax: in one monstrous specimen it bore a single cirrus, showing (if there had been any doubt) that it was a true segment. The three terminal pairs of articulated appendages, form together a brush; they consist of the fifth and sixth pairs of cirri and of the caudal appendages: my reasons for considering the last-named organs as of caudal origin will be given hereafter. A moderately careful inspection, especially of the ventral surface, will show that the fifth pair of cirri are borne on a small segment (n, fig. 5, but plainer in fig. 13), which is quite distinct from, but partially concealed by, that which ought to bear (and did bear in the monstrous case) the fourth pair of cirri: this segment is oblique, and cannot be traced distinctly all round the dorsal surface. The segment (o, fig. 13) bearing the sixth pair is much less distinct, and can only be seen by a longitudinal section, or when the cirri are a little separated, but it certainly exists,[144] as is likewise shown by the presence of small apodemes dipping in amongst the muscles, between this and the last segment. The posterior or caudal appendages are closely approximated; they are not separated by any fold from the sixth thoracic segment; but appear as if they were articulated on the dorsal surface of the sixth pair of cirri, in exactly the manner usual in the other Lepadidæ. The segments bearing the fifth and sixth pairs of cirri are highly oblique to the preceding segments, and consequently the cirri, which they support, instead of projecting inwards, lie like a brush in a line with the longitudinal axis of the main part of the thorax. The membrane forming the two small oblique terminal segments of the thorax is strengthened by irregularly shaped plates of thicker and yellowish membrane.

[144] In the middle, the fold is slightly prominent and pointed, and being most finely villose, I for some time looked at this projection as a rudiment of the probosciformed penis.

Mouth.--The mouth is constructed on the strictly normal type of the Family, but is peculiar in every part; it is remarkable from being situated so near the upper (or posterior) end of the capitulum, this being caused by the great length of the labrum, and of the space of body between the latter and the lower end of the orifice. The labrum is a very singular part of the mouth from its vast size and outline: in fig. 8, we have a front view of the mouth, of which the whole upper pointed part consists of the labrum, and h h is the first pair of cirri; in fig. 11, we have a lateral view of the labrum, with the surrounding thin membrane of the body, a--a, still adhering to its edges; h is the first cirrus on the near side; m the mandible, a little distorted in order to show its tooth, marking the position of the transverse crest of the labrum and of the orifice of the œsophagus; b b is the medial longitudinal ridge of the labrum. In the Balaninæ the labrum forms a mere rim to the back of the mouth, consisting of an inner fold running down the œsophagus, and of an outer fold, both close together: in the Lepadidæ the folds are separated, the outer one being swollen or bullate; and here this structure is carried to even a greater extreme than in Ibla and its allies. The distance between the transverse crest over the œsophagus and the blunt projecting point on the summit of the medial ridge, b b, equals twice the longitudinal diameter of the rest of the mouth. The lower margin on each side of the labrum is produced into two projections (fig. 11), the longer one curling round to a point beneath the jaws, with its extremity imbedded as an apodeme. Another very peculiar character in the labrum, prominently noticed by Mr. Hancock, is caused by a longitudinal row, on each side, of closely approximate, long, very finely pointed hairs, which, as already stated, are fronted on the opposed internal surface of the sack by an irregular band of still finer hairs. The surface of the labrum is partially covered by minute toothed scales, and these, seen on the longitudinal medial ridge, b b, give it a finely denticulated structure. At each end of the transverse crest which overhangs the œsophagus, there is a knob, such as occurs on the labrum of every Cirripede. United to these two knobs, which are formed of thick and yellowish membrane, and springing from the adjoining sides of the mandibles, there are two swellings formed of thin membrane (fig. 8), which occupy the exact position of the palpi, and may be considered as these organs in a rudimentary condition and destitute of bristles.

The mandibles are simpler than in any other Cirripede; they are minute; they consist of an oblong plate, with only one very strong tooth at the upper end: the face towards the labrum is swollen: beneath the upper free part there is a small, sub-triangular piece of thickened membrane, let in and forming part of the general outer surface of the mouth, and representing the large square plate found in other Cirripedes. The maxillæ (fig. 15) are smaller but broader than the mandibles; they have an upper tooth and a smaller lower one, lying not quite in the same plane with the upper one, but nearer the mandibles. The apodeme (fig. 8, 15) is of remarkable length, extending beneath the basal fold of the mouth: it does not arise from the ridge or outer edge of the maxilla, but a little on one side, from the face directed towards the mandible. Between maxillæ and mandibles there is a very singular prominent fold of membrane (fig. 8, 15), which resembles, but probably falsely, the supposed rudimentary palpus attached to the mandible. Altogether the maxillæ differ considerably from the same part in other Cirripedes. In structure they seem adapted to assume the function of mandibles; but they do not stand directly over the œsophagus. The outer maxillæ (fig. 8) appear like a minute, deeply notched lower lip: each consists of a simple, oblong, rounded plate, with a few small bristles at its upper end. The basal fold of the mouth in front, beneath the outer maxillæ is distinct, and runs in a line with the basal articulation of the first pair of cirri. In the rudimentary palpi, minute and little developed outer maxillæ; and in the inner maxillæ, taking the function of the mandibles, the mouth of Alcippe presents some resemblance with that of Anelasma.

Cirri.--These consist of the first, fifth, and sixth pairs: the other pairs are absent, except in one monstrous specimen, in which there was a fourth cirrus quite like the fifth. First pair, fig. 14, these are seated on each side of the mouth in the usual position. They are formed of very thin and flexible membrane. The pedicel, as usual, consists of two segments, the upper one is short and not very distinct; but when viewed on the inner side can be seen to have the ordinary structure: both segments are destitute of bristles. There are two short rami, being about one third of the length of the pedicel: they are directed either in the line of the pedicel, or more commonly posteriorly, that is towards the other cirri, and therefore in an unusual direction. The anterior ramus is generally rather longer and thinner (as is commonly the case with other Cirripedes) than the posterior ramus; but there is some variation in this respect. On neither ramus is there any trace of the ordinary articulations: both are thickly clothed with fine bristles, which are singular from being thickened in their lower parts, and plumose, like a feather. These cirri have some resemblance, as remarked by Mr. Hancock, to a pair of pincers; but they cannot act as such; they serve, I believe, as brushes. Delicate muscles, transversely striated, enter and are attached within both rami and within both segments of the pedicel, on the usual type, showing that these organs (if there had been any doubt) are truly cirri.

The fifth and sixth pairs of cirri (fig. 13, n′, o′) are almost exactly alike: they are of very small size: each cirrus consists of four segments: the lower or basal segment is broad, with a few minute bristles scattered on its inner surface: the second segment is also broad, but shorter, with a few, generally hooked bristles, in two short irregular rows, in the upper part: these two segments answer to the two segments of the pedicel of ordinary cirri. The third segment is thinner and longer than the second; it bears two or three longitudinal rows of bristles, most of which are neatly hooked at the point; its upper end is surrounded with a circle of bristles. The fourth and terminal segment is short, thin, and simple, with only a few bristles at the apex. These two upper segments are bent a little inwards; they answer to one of the two normal rami of ordinary cirri. The third segment does not stand exactly on the middle of the summit of the second segment,--the posterior corner of the latter being occupied by a very curious, convex, oblong, rather hard (especially in the lower part), protuberant cushion (as called by Mr. Hancock) or button (fig. 9, c′), transversely wrinkled by fine, distinctly crenated ridges. This button presents a considerably different appearance according to the point of view, fig. 9, 10: on one of its sides it projects beyond the outline of the second segment, whence it arises; on the other side it is prolonged, as a smooth ridge, on the top of the second segment, embracing to a certain extent the base of the third segment. On the face opposite to that which has been drawn (fig. 9) as most characteristic, it is seen to be somewhat constricted round its base; this constriction, representing, I believe, an articulation. When viewed directly in front (fig. 10) its outline is oval, passing into shield-shaped. Its longitudinal axis is 3/1000ths of an inch in length; but it varies a little in shape and size. I shall presently assign my reasons for believing that these buttons are the posterior or inner rami of the fifth and sixth pairs of cirri in a rudimentary and much modified condition.

Caudal Appendages.--These (fig. 13, p) are placed close together, being articulated between the bases of the sixth pair of cirri, the lines of junction being internally marked by minute apodemes. They consist of four segments, resembling in every respect those forming the cirri, with the important exception that there is not a vestige of the button on the summit of the second segment; the segments are not so thick as those of the cirri, and the terminal segment is smaller.

Muscles and Functions of the Cirri.--For their size, the cirri and caudal appendages have voluntary muscles of remarkable strength, attached within their basal segments, and springing from the dorsal and ventral surfaces of the so-called third and fourth (l, m) thoracic segments. Other muscles, rising from within the basal segment of each limb, run to the second segment, and from that to the third segment. I could not distinctly make out whether any entered the terminal segment. I have seen no other instance of muscles entering the caudal appendages, but as in the pupa they are so furnished, we here have only an embryonic character preserved. I may remark that the fifth and sixth cirri, consisting of two large basal and two thinner terminal segments, is likewise an embryonic character. From the position of the cirri, the four hard protuberant buttons or cushions, tend to oppose each other at a common point; and the caudal appendages fill up a gap behind, between the cirri of the sixth pair. I at first thought, with Mr. Hancock, that these buttons served to catch the prey; but, reflecting on their convexity and hardness, they appear very badly adapted for this purpose; it would, in fact, be a marvellous feat to secure, in the dark, any moving object between four balls. On the other hand, this very convexity, the hardness, and especially the crenated ridges, and the powerful muscles (which from the first surprised me), are all well explained, if we suppose the prey, being secured by the terminal segments, to be triturated between these four balls: any part which escaped upwards would, moreover, be retained in a sort of cage, formed by the inwardly inflected terminal segments with their hooked spines. This view of the very curious and unparalleled use made of a modified portion, not of the haunch, but of an upper part of the two posterior pairs of thoracic limbs, is in some degree confirmed by finding that Cryptophialus, which has apparently analogous habits, requires its food to be triturated, though in this case it is effected by very different means, namely, by four beautifully toothed discs, with brushes of hairs, developed within the lower end of the œsophagus.

The prey, when caught, would probably at once be carried by the movement of the articulated thorax to the mouth (itself moveable), and being there secured by the mouth in front, the caudal appendages behind, the tips of the cirri above, and the broad pedicels of the first pair on the two sides, it would be triturated by the four crenated buttons, and would then be forced down the œsophagus by the action of the simple jaws. I looked in vain in several specimens for any object within the stomach. I believe, that when the specimens are first taken, all half digested food is ejected by the mouth. Whether we may thus account for the extremely foul condition of the rami of the first cirri in all the many specimens examined by me, I know not; but that these rami, which are thickly clothed with fine plumose hairs, and are furnished with delicate muscles, act as brushes, so as to clean the orifice of the sack, I can hardly doubt.

Homologies.--I have as yet, to a certain extent, assumed that I have correctly named the different parts; and a few remarks on this head may be desirable, considering the absence of certain cirri, the singular condition of the others, the close general resemblance of the cirri and caudal appendages, and the fact of the latter being furnished with muscles. The only cause for any doubt regarding the thoracic segments is the shield of thick membrane on that segment (k, fig. 5), which ought to have borne the second pair of cirri, causing two transverse wrinkles (not distinguishable, however, on the ventral surface), and sometimes making the segment appear as if it consisted of three segments: if it did consist of three, as there can be no doubt about the nature of the first pair of cirri, (not in a more rudimentary condition than in Anelasma) or about the segment whence this first pair arises, the two terminal oblique segments, with their appendages, would be abdominal instead of thoracic: but this is improbable, inasmuch as the abdomen is unusually little developed in the pupa (as presently to be shown), and more especially from the circumstance of a monstrous cirrus, identical in structure with the two succeeding pairs, having been borne on a segment (m), which, in any case must be considered as thoracic, for it is well known how very rarely thoracic and abdominal limbs resemble each other. I cannot myself feel hardly any doubt on the nature of these three pairs of appendages; for, in the first place, the posterior appendages are articulated on and between the bases of the adjoining pair, exactly as the undoubted caudal appendages are articulated in all other members of the family on the sixth pair of cirri or terminal thoracic appendages. Secondly, we see in the male of the allied genus Ibla, the very same appendages preserved as in Alcippe, namely, the caudal, and the fifth and sixth pairs of cirri, which latter, moreover, are generally uniramous. Thirdly and lastly, in the likewise allied Alepas cornuta, we have the posterior rami of these same fifth and sixth pairs of cirri in a rudimentary condition, and resembling in every respect the caudal appendages. Assuming, then, that the several appendages in Alcippe have been rightly denominated, we have to consider the nature of their segments: in all cirripedes, the pedicels of the cirri consist of two segments, of which the lower one (as here) is longer than the upper one, and both (as here) considerably thicker than the segments of the rami: in all cirripedial pupæ, likewise, the thick pedicels of the limbs consist of two segments, and each ramus, also (as here), of two segments: now, with these coincidences, and bearing in mind that in Alcippe the two upper segments do not arise from the exact middle of the summit of the second segment, but from rather its anterior side,--bearing, also, in mind the case just cited of Alepas cornuta with the posterior rami of these very same cirri rudimentary,--we may, I think, safely conclude that here in Alcippe the two lower segments form the pedicel; the two upper segments, the anterior ramus; and that the button-like protuberance is the posterior ramus in a modified condition. As the caudal appendages in none of the Lepadidæ, either in the mature state or in the pupa, have two rami, we can satisfactorily understand the absence of any trace of the button-like protuberance on the top of the second segment.[145]

[145] I almost wish I could persuade myself that I had taken an erroneous view of the thoracic segments, and therefore that the three pairs of terminal appendages were all abdominal, for then Alcippe would come into much closer relationship with Cryptophialus; though even in that case it would form a distinct family from it: but I cannot alter my opinion.

Alimentary Canal.--The œsophagus runs down from the mouth, beneath and nearly parallel to the straight row of hairs on the two sides of the labrum: it is surrounded by the usual muscles: at the lower end it bends down, and expanding a little, like a bell, enters the stomach. The stomach is of considerable size and fills the main part of the body, bulging out under the mouth, and prolonged as far as about the middle of that segment (l), which ought to have borne the third pair of cirri; here the stomach terminates in a blunt rounded point. The tissue surrounding the stomach, and keeping it in its proper place, can be traced to the posterior end of the thorax, but there is no rectum or anus. I am prepared to assert positively that this is the case,[146] for I made repeated longitudinal sections of the whole thorax in two planes, and I subsequently cleaned the outer tissues with boiling potash, and then, when as transparent as a sheet of glass, I examined every part, and certainly there is no rectum (which in every case is formed of chitine, and so is not acted on by potash) nor an anal orifice. Singular as this fact is, it is not so improbable as it at first appears; inasmuch as I have shown, in my former volume, that the Lepadidæ can reject half digested food by their mouth, and secondly, that the final stage of digestion appears to take place in the upper part of the stomach. In the male of this very species, as we shall immediately see, there certainly is no mouth or stomach, and apparently no rectum or anus; so is it likewise with the males of Scalpellum vulgare and ornatum: in Proteolepas, there is a mouth and an œsophagus, but no stomach, rectum, or anus. There are, I believe, no other known instances, in the whole great class of Crustacea, of the absence of an anus.

[146] I may venture to remark that I succeeded in every attempt, which I made, in seeing plainly the œsophagus, and the acoustic and olfactory orifices and sacks, which, according to all analogy, would be of much smaller size, and far more difficult to discover, than the rectum and anus. I may mention that, according to Mr. Newport ('Annals of Nat. Hist.,' 1849, p. 277), the larvæ of certain parasitic Hymenoptera have a stomach without any anus. No crustacean, according to Milne Edwards, is destitute of this orifice.

The stomach, in Alcippe, is much corrugated, so as to be deeply pitted; but there are no regular cæca. The enveloping hepatic layer is thick, brownish, pulpy, and formed of pellets of cellular matter, not distinctly arranged in lines as is general; there is the usual delicate muscular layer. The stomach was in every case empty, and I did not notice the separated epithelial coat, so generally found in other cirripedes.

Organs of Sense.--I failed in discovering the eye, which I have no doubt exits, as it is conspicuous in the pupa and in the male. The olfactory pouches are seated rather laterally under the maxillæ, as in Ibla. As in this same genus, the acoustic sack is seated remarkably low down (fig. 5), at a very considerable distance beneath the basal articulation of the first cirrus: the orifice is seated on a slight prominence: the acoustic vesicle, I believe, is sub-cylindrical, with irregular projections. I did not make out anything distinctly on the nervous system.

Female Generative System.--The animal we have thus far described is exclusively female: when a longitudinal section of the thorax is made, and the stomach removed, it can be most plainly seen that there are no vesiculæ seminales or testes. Mr. Hancock has remarked on the absence of the usual probosciformed penis. The male of Alcippe will be subsequently described in detail. The female organs differ in no respect from those of other members of the family, excepting in so far that the layer or mass formed by the ovarian cæca (c) does not lie transversely to the longitudinal axis of the whole animal, but longitudinally under the horny disc. The ovigerous fræna are largely developed, but serve, as previously stated, as branchiæ, and not for their proper function of giving attachment to the ovigerous lamellæ. The ovigerous lamella is single, and nearly corresponds, in size and shape (as would ensue from the manner of its formation) to the under side of the horny disc. The ova are broadly oval, and rather above 1/100th of an inch in length.

Metamorphoses.--The larva in the first stage has been fully described and figured by Mr. Hancock: it differs in no essential respect from other larvæ of the family. Mr. Hancock overlooked the inferior minute antennæ. With respect to the larvæ in the last stage, or pupa, I obtained several specimens attached to the disc of the female, and which were on the point of being developed into males; and another specimen identical in all respects, but attached independently to the shell of the mollusc, and which, therefore, I have every reason to suppose, would have been developed into a female. In any case these pupæ may be conveniently here described (Pl. 23, fig. 16.) They are .025 of an inch in length; they are of the usual shape, with the anterior end not very blunt and the postero-ventral surface somewhat produced. The whole carapace or shell is very thin and smooth. There are six pairs of thoracic natatory legs, situated far back towards the posterior end of the body; each leg has the usual articulations, and the two rami their usual long but not plumose spines; the presence of the legs deserves notice, considering the rudimentary and modified state of their homologues in the mature animal. The abdomen differs considerably from the same part, as far as I have seen, in other pupæ; it consists of only a single almost globular (fig. 17, q) segment, instead of three segments; and the two caudal appendages (r) are very long, and are composed each of only a single segment (instead of two), carrying at its tip two short spines. There are two purple eyes, 4/3000ths of an inch in diameter, which, after having been dried and then soaked, could be seen to be compound; they are fixed in the usual manner to two rather short apodemes, which latter have their usual origin. But the pupa has a very unusual appearance owing to the presence of a single dark purple eye, half the diameter of the two larger eyes, situated behind and above the latter, and quite disconnected with the apodemes; this is the eye of the mature animal, which, for some reason, is here developed earlier than usual. The prehensile antennæ are remarkable from being seated very close to the anterior extremity: owing to this, the articulation of the second or main segment with the basal segment, is hardly at all oblique. The whole pupa is of exactly the same length as the pupa of Ibla quadrivalvis, and so are the antennæ, (see p. 286 of my volume on the Lepadidæ), viz., 32/6000th of an inch, but the second segment is narrower, (being only 8/6000ths in breadth in the broadest part), and is longer in proportion, for the disc which forms part of the total length is only 4/6000ths in length, whereas in Ibla it was 8/6000ths; the disc is here hoof-shaped, as in Ibla. The ultimate segment is remarkably short and narrow, (being only 3/20000ths in width, and less than half the size of that in Ibla); it carries (I believe) three terminal spines, and is not notched. Altogether the antennæ more nearly resemble those of Ibla than of any other genus in the family. From the position of the antennæ, and from the length of the second segment, the pupa, when cemented by the disc or third segment, to the supporting surface, adheres, with its posterior end almost vertically upwards. With respect to the young cirripede within the pupa, I could only observe that its anterior end was formed into a blunt point.

Powers of Excavation; Inorganic Deposit of Calcareous Matter; Attachment.--Alcippe, according to Mr. Hancock, attacks only dead shells of the Fusus and Buccinum, and always on their inner sides, especially on the columella. The excavations, in the specimen which I examined, were so numerous as almost to touch, and sometimes to run into each other, the included animal being thus rendered distorted. The orifices are directed with respect to the shell indifferently upwards or downwards. From the shape and size of the cavity corresponding to that of the included animal, there can be no doubt, as stated by Mr. Hancock, that Alcippe forms its own cavity. That the action is mechanical I think may safely be inferred from the whole outer membrane being studded with minute, star-headed points of hard chitine, which rise from halo-like little discs of thickened membrane, which latter are well adapted to allow the underlying adherent muscular layer to act on the points, and thus on the surrounding shell. Consequently the points generally show signs of severe attrition, but they are periodically and often replaced, at each exuviation, by new and much sharper points. There are no points on the permanently attached layers of the horny disc, but it particularly deserves attention, that the renewable membrane always extends beyond the circumference of the disc, and is there most thickly studded with the points. We have met, in Lithotrya, with a precisely analogous fact in the extension of the periodically moulted membrane of the peduncle, furnished with star-headed points of chitine, and in addition with minute calcareous beads (which, however, seem soon worn away), beyond the calcareous discs, by which this cirripede is attached in its cavity. We need not feel much surprise at points of chitine being hard enough to wear away shell, when we consider what work the jaws of insects, likewise formed of chitine, will effect.

With respect to the first commencement of the excavation, the pupa, owing to the position of its prehensile antennæ, fixes itself with its posterior end almost vertically upwards; and the young cirripede, after its metamorphosis, from the greater length of the ventral integuments formed round the eye-apodemes, must be thrown backwards into nearly the position represented in Pl. 22, fig. 12, b. I have not seen a young female at this early age, but I have traced the development of several males, and have found that the lower end of the peduncle, (i. e. what was the anterior end of the pupa), grows at quite a remarkable rate, so as very soon to form a great bag extending beyond the attached prehensile antennæ. Now if we suppose an analogous structure in the female or ordinary Alcippe, and the supposition is quite allowable, we shall almost immediately have the anterior or lower end of the young cirripede, just in advance of its antennæ, pressing against the surface of the shell of the mollusc; and if armed with triturating points, as we have every reason to believe it is, it would wear for itself a cavity. The horny disc on the ventral surface of this protuberant anterior end of the young animal will, we may assume, soon become cemented to the near side of the cavity just supposed to have been excavated. And the whole animal, by further slight changes in direction, namely, by working down more and more obliquely, will take, as shown at (c), its final position. As the whole surface of the animal, with the exception of the horny disc, is provided with triturating points, the animal, when once imbedded, can and does increase its cavity at both ends in length, in depth, and all round the edges of the horny disc,--in short, in every direction excepting directly over the horny disc. I believe, as already explained, that the young Alcippe, (b, diagram), first bores obliquely into the shell; and whatever amount of downward extension the horny disc attains before the young cirripede assumes its proper position, with its ventral surface upwards and parallel to the inner surface of the shell of the mollusc, that amount determines the thickness of the plate of shell hereafter to be left unabraded over the horny disc, as the latter continues to extend in circumference. This plate of shell over the horny disc is so thin, that, as mentioned at the commencement, the colour of the ovaria is seen through; and until I reflected on the following considerations, I was much surprised how the instinct of the animal could so neatly guide it not to grind too deeply, and yet to grind till only a very thin plate of shell was left over its horny disc: these considerations are, that whatever thickness was first given to this plate of shell, when the animal was very young and first assumed its ultimate position, that thickness would in most cases be always retained, owing to the flatness of the disc, and to the membrane armed with triturating points protruding very slightly beyond and above the horny disc, only just enough to wear away the surrounding shell to the thickness necessary to allow of the formation of each new zone of disc; as the disc itself is not armed, it subsequently has no power of wearing away the plate of shell above it. Thus the horny disc, besides giving support and attachment to the peduncle, is of this peculiar service that it seems to guide, (somewhat like the wood-part in a plane), the rasping powers of the lower extreme margin of the peduncle.

I may here observe that certain radiating and often punctured lines, mentioned and figured by Mr. Hancock, which help to render the thin plate of shell over the peduncle conspicuous (fig. 3), are formed by the burrows of an excessively minute annelid, the punctures being apparently the exit orifices: I imagine that these annelids find it difficult to commence their burrows on the smooth surface of the shell, and that they congregate at these particular spots and thence burrow in radiating lines, owing to their having taken advantage of the little cliff-like edges, at the narrow and disused ends of the fissures leading into the cavities occupied by the Alcippe, where alone they would not be disturbed by the action of the cirri, when first they commenced making their little burrows in the shell.

The fissure leading into the cavity is required to be broad at the posterior end, in order that the cirri may be there freely exserted out of the sack; and narrow in other parts, to prevent, as it would appear, anything injurious getting in between the animal's body and the cavity in the shell of the mollusc. As the fissure is increased in length by attrition at the broad posterior end, which end during growth becomes broader and broader, the lower part of the fissure has to be narrowed, and this is effected in a very singular manner, namely, by advantage being taken of the strong tendency, which triturated shell with animal matter, has to set into a solid shelly mass, although constantly agitated.[147] Mr. Hancock noticed this edging of hard shelly matter, and naturally thought it was a secretion. Lines of deposition (Pl. 22, fig. 4, b), parallel to the edges of the furrow can often be perceived in it: its thickness and extension vary much: I have seen it on one side alone of the orifice: it is, of course, never found at the broad end where the process of enlargement goes on. The peculiar worn surface with which it irregularly thins away downwards, on the sides of the cavity, made me (together with the apparent impossibility of such a secretion proceeding from an animal wholly invested by a chitine membrane) suspect it to be inorganic; and this view is certainly correct, for when a fragment is dissolved in acid, a considerable residuum is left of bits of membrane, rubbish, and, in one instance, even of the remnants of a foreign animal, apparently an annelid. We have here all the circumstances favorable for inorganic deposits of this nature, namely, finely triturated shell and chitine or animal matter, produced by the excavation of the chamber, sea-water, and movement.

[147] I have given some remarkable cases in my volume on 'Volcanic Islands,' (p. 49), in which limestone, having almost the hardness and specific gravity of marble, has been thus deposited. Almost every coral-reef offers similar examples. The curious substance described by Mr. Horner and Sir David Brewster, ('Philosoph. Transact.,' 1836, p. 65), which is formed during the manufactory of cloth, offers another example of the strong tendency which lime and animal matter have to unite. Lately, Dr. Horsford, in 'Silliman's North American Journal,' Jan. 1853, has discussed the chemical theory in an analogous case on the coast of Florida; he attributes the aggregation to the formation of a hydrate of lime through the action of the animal matter. Mr. G. B. Sowerby, Junr., has described a case very analogous to that of Alcippe, ('Proceedings of Zoolog. Soc., Mollusca,' Pl. 5, fig. 4, p. 162, 1850), namely, that of Pholas calva, in which a tube is formed of inorganic calcareous matter, serving to narrow the entrance.

From the manner of growth of the animal, the fissure leading into the cavity in the shell becomes much longer than the orifice leading into the sack, and to prevent the body being unnecessarily exposed, the upward projection of the disc, already described, is formed under the narrow and disused end of the fissure; moreover, the two rims of the inorganic calcareous deposit sometimes here approach so closely, as almost or actually to touch each other; and between them, as remarked by Mr. Hancock, there is usually a little accumulation of grains of sand. This narrow end of the fissure is generally curled either to the right or left hand; and I can only account for this fact by supposing that, whilst the cirripede is young, and has not a large horny disc attached to the cavity, it cannot keep its body straight during the long-continued boring process.

The animal is attached by its horny disc to the thin shelly roof over the peduncle, and likewise to the under side of the narrow end of the fissure, but is elsewhere quite free. I carefully examined the disc in many specimens, but could not see any cement-ducts: I believe I saw layers of cement at the upper end of the disc, but it is not easy to discriminate between this substance and the yellowish, somewhat disintegrated, layers of the horny disc. The pupa certainly becomes attached by ordinary cement, so that the attachment in early life, at least, is normal. In some full-grown specimens, I found the lower parts of the horny disc attached, along the edges of the layers, to the roof of shell; and as I looked here in vain with the highest powers for cement-ducts, or for cement, it appears to me probable that the rough edges of these layers were united to the roof by a thin layer of the inorganic calcareous deposit. The animal, from its very protected situation, certainly requires to be less firmly cemented than other cirripedes; and even in Lithotrya, which is less deeply imbedded than Alcippe, the cementing apparatus was feebly developed. From the length of the pupal antennæ, cemented by their terminal segments, the position of the young cirripede (Pl. 22, fig. 12) can be changed to a considerable extent, like a ship swinging at her moorings, but in order to assume its final position, the animal must, I think, travel like Lithotrya, but to a much less extent, by a short succession of overlapping horny discs,--the old discs being partially deserted, each new one extending beyond the last-formed one: even in the case of the mature animal, we have seen that, under certain circumstances, it changes, to a certain extent, its position; portions of the old disc being deserted and attached to the roof of a deserted portion of the cavity.

Affinities.--In the preliminary remarks under the Family, I have discussed this subject almost sufficiently: I will here only remark, that the genus, though so abnormal, yet stands naturally between Ibla and Anelasma, having clear affinities, on the one side, through and beyond Anelasma to Alepas; and on the other side, beyond Ibla to Scalpellum, and so to Lithotrya. Moreover, it is very distinctly related to Cryptophialus in the succeeding Order.

MALE. Pl. 23.

On every specimen of the female Alcippe, which I carefully examined, I found some minute parasites (or epizoons) attached to the lateral edges of the upper part of the horny disc, and therefore lying within the narrow end of the fissure leading into the chamber excavated in the shell of the Buccinum. Although having had some experience in the very anomalous forms which male cirripedes assume, yet when I first casually inspected these parasites under a weak lens, from their transparency, their elongated and lobed body, including an internal folded up organ, I actually threw them away, thinking that they were probably Bryozoa. Subsequently, a more careful inspection immediately showed the cemented prehensile antennæ, and their cirripedial nature was demonstrated. I soon found specimens with the perfect still adherent exuviæ of the locomotive pupa, undistinguishable from the pupa already described as probably belonging to the female Alcippe. But as this latter fact, may perhaps be doubted, I must show that there is other evidence sufficient to prove that these cirripedial parasites are the males of the female Alcippe. Of the females, I inspected many specimens, and all certainly were without external male organs; and in the four or five specimens which I rigidly examined, there were no testes or vesiculæ seminales, the latter being in all hermaphrodite and male cirripedes so conspicuous. On the other hand, I examined at least thirty specimens of the parasite, and they were all exclusively males, for all had a probosciformed penis, and the greater number had their vesiculæ seminales filled with spermatozoa, and hence were ready to perform the act of impregnation, but undoubtedly they contained no ova. It would, then, be very strange, if these two cirripedes of opposite sexes, thus attached together, were not sexually related. Wonderfully different as the parasite is from the female Alcippe, yet, in one very important character it is related to Alcippe, and to no other member of the Family, namely, in the sack extending down to the extreme lower point of the peduncle; the male organs, I may add, occupying an analogous position with the peculiar position of the female organs in Alcippe. The lateral lobes of the peduncle in the parasite seem to represent the sides of the broad depressed peduncle in Alcippe; and in both the peduncle grows at its lower end--a very rare circumstance--observed only in two genera in this Family, namely, in Anelasma, and in a slight degree in Lithotrya. Besides these points of resemblance between Alcippe and its parasite, which are striking, considering their external utter dissemblance, the affinities of both point, judging from certain small characters, in the same direction, namely, towards Ibla and Alepas. Finally, then, I think, we may confidently admit that this parasite or epizoon is the male of the female Alcippe: indeed, considering the facts given in my former volume, on Ibla and Scalpellum, I have, perhaps, here discussed the question at unnecessary length.

The males are generally attached, as already stated, to the two hollowed out sides of the upward prolongation of the horny disc; they adhere by means of little patches of cement, proceeding from the terminal segments of their antennæ, to the overlapping edges of the few later-formed zones of the disc; hence, they lie protected, within the narrow end and a little under the edges of the fissure leading into the cavity in which the female is lodged. In some specimens, however, the males are attached rather lower down on the disc, and are not confined exclusively to its upper margin, so that they live fairly under the roof of shell which covers the main part of the disc: but they are never attached very low down, so as to lie far from the lower end of the orifice leading into the sack of the female. I have two or three times seen as many as three males on each side, but sometimes there is only one on each side, or none on one side. A large distorted specimen actually had twelve males, and two pupæ on the point of undergoing their final metamorphosis, all fourteen attached on one side, and all evidently must have been alive together! Another specimen had nearly the same number, a few on one side, and the rest on the other side.

The male immediately, after the exuviation of the pupal carapace, 25/1000th of an inch in length, is only 23/1000th of an inch long, but ultimately it becomes, chiefly from the growth of the lower end of the peduncle, nearly twice this length; for the largest specimen which I have seen, that figured, was 45/1000th of an inch long (i. e. under 1/20th of an inch), and 1/100th of an inch in breadth across the peduncle, beneath the lateral lobes. The whole external membrane of the animal (as well as the internal membrane of the sack), is very thin, quite structureless, and as transparent as glass; hence, even the spermatozoa, within the vesicula seminalis, can be seen from the outside. The whole structure of the animal is very simple. The ventral surface can be at once recognised by the attachment of the antennæ (fig. 19, a), and these organs mark the point which was the anterior end of the male, just at the period of its metamorphosis, and before the lower end of the peduncle had grown. These antennæ have already been fully described; they are conspicuous from being composed of membrane, rather thicker than that investing the body of the male, and which external membrane can be traced entering these organs, and appearing like cement-ducts; but within these tubular prolongations of the outer membrane, I could obscurely see the real cement-ducts.

The part answering to the capitulum is much flattened and elongated; it widens but little from the upper to the lower end, where it blends with the carinal or dorsal surface (the under surface in fig. 19) of the lobed peduncle. At the upper end there is a small orifice, and close to this, on the ventral or rostral side, there is a thin, apparently double projection (i, fig. 19) or flap of membrane, one flap lying exactly over the other. The whole length of this capitulum probably corresponds with that small portion of the capitulum in the female, between the upward prolongation of the horny disc and the lower end of the orifice; and the two broad flattened projections in the male, probably answer to the two sharp narrow points (a, fig. 1, Pl. 22) in the female. The peduncle has two lateral lobes (h, g, fig. 19), and, whilst young, what may be called a third and medial lobe, but this soon increases largely by growth, and forms the main part of the peduncle. The lateral lobes are intimately connected with the ventral surface; they tend to lie in a plane, at right angles to the compressed capitulum, but owing to the excessive thinness and flexibility of the whole external membrane, it is difficult to ascertain the relative position of the different parts. Moreover, owing to the pupa being so much flattened, these lobes are necessarily formed folded up; and, I believe, it depends on the position, with respect to surrounding objects, which the male ultimately holds, whether the lobes ever assume, their apparently normal position, in a plane at right angles to the sides of the pupa; owing, also, to the form of the pupa, the two lobes seem generally to be actually formed of unequal sizes, that formed in the dorsal region of the pupa being the largest. I believe that these lobes correspond with the lateral margins of the upper end of the peduncle of the female, which margins project laterally beyond the sides of the capitulum. The lower lobe, or end of the peduncle, is depressed in the same plane with the lobes; it is of variable length; when first formed it hardly extends beyond the basal articulation of the prehensile antennæ. Commonly it does not lie quite in a straight line of the capitulum; and I have seen specimens in which it stood at nearly right angles to the capitulum and to what was the ventral surface of the pupa; this irregularity in the relative position and sizes of the different parts of the peduncle, no doubt, to a considerable extent, depends on the form of surface to which the male becomes attached, just in the same way as we have seen that the peduncle of the female becomes altered in shape during the excavation of the chamber in which it is lodged.

I feel some difficulty on one point: in the pupa the single eye of the future male can be clearly distinguished, and it lies some way from the anterior end of the body; but in two males, which certainly had just moulted, and in which none of the internal organs were as yet developed, the eye lay close to the anterior end, directly over the basal articulation of the antennæ. I suspect this is somehow caused by the great change of form which supervenes, during the metamorphosis, at this anterior end of the body; the extremely compressed body of the pupa having to become depressed and lobed in the young male. I have given a figure of a young male, just as it appeared (Pl. 23, fig. 18), somewhat distorted from lying on a flat surface; c, being the eye.

The sack extends, in a very remarkable manner, down to the lower end of the peduncle, the whole inside of the animal being thus freely open to the water. In the upper part, the sack forms a mere narrow tube; it does not appear to have been formed in the same manner as in all other cirripedes, namely, surrounding the thorax and natatory legs of the pupa, but in an abnormal position, along the dorsal surface, above the sack and thorax of the pupa: a transparent line, where the new narrow sack is in process of formation, is the first indication of the coming metamorphosis. The sack in the capitulum of the male is not central, but lies near the dorsal surface; the ventral interspace, between the outside and the sack, is occupied by oblique fibres (l, fig. 19), which may be striæ-less muscles, but I suspect are ligamentous fibres, giving support to the whole projecting capitulum. These fibres enter a little way within the lobed peduncle; they are probably homologous with the strong muscles, which run from beneath the upper end of the horny disc of the female to the lower end of the orifice leading into the sack. Round the lobed peduncle,[148] there are two bands (e, f) of thin muscular fasciæ, slightly oblique to each other, and attached at the ends to the outer membrane; they are evidently homologous with the external transverse muscles, which are best developed round the same part in the female. Some of these muscles present a singular chain-like appearance, from being strangled at intervals: they act probably in aiding the long probosciformed penis to protrude itself out of the sack. I could not detect any longitudinal muscles, and the lower part of the peduncle seems destitute of muscles of any kind.

[148] I believe I saw in one specimen, most delicate transverse muscular fibres round the lower part of the elongated capitulum.

The internal structure of the animal is very simple. Within the lower end of the peduncle there is a dark purple eye (c), under the 1/1000th of an inch in diameter, a testis (d) and a (b) vesicula seminalis. These organs falsely appear as if suspended in the middle of the peduncle, but they are really attached, I believe within a separate partition, to the ventral surface, occupying the same position as the mass of ovarian cæca in the female. The eye lies on the line of junction between the testis and the vesicula seminalis, and on their ventral side. The testis is rounded, and consists of a mass of cells, on an average 1/5000th of an inch in diameter. The vesicula seminalis varies extremely in condition, being either a mere rather broad vessel, enlarged where it joins the testis, or a bag fully as large as the testis itself, and distended with spermatozoa, all arranged parallel to its longer axis. There was an evident relation between the size of the vesicula seminalis and that of the testis, the number of the cells in the latter decreasing as the mass of the spermatozoa increased: there was also an evident relation between the age of the male and the state of these organs; younger and more opaque individuals, having their testes of large size; and older specimens, with the lower end of the peduncle arrived at its full dimensions, having the vesicula distended. Some few old specimens had evidently discharged their spermatozoa. By dissection I more than once distinctly traced the vesicula seminalis entering the broad lower end of the penis. The membrane, forming the vesicula, is ringed, and I presume is, as in other cirripedes, contractile, so as to expel the spermatozoa. The probosciformed penis (m) is of extraordinary length: it is plainly ringed, or rather articulated, in this respect resembling that organ in Ibla and Alepas; it tapers gradually, and terminates (as usual) with a brush of fine bristles; it is furnished with delicate voluntary muscles, arising from the body round its basis, and extending no doubt up to the apex, but too fine to be traced all the way. Its broad lower end is attached in a slight depression, on the ventral side of the sack, a little above the point of attachment of the pupal antennæ. According to all analogy, the spot whence the penis springs must be considered as representing the thorax and abdomen; and the outer membrane of the penis is here, as on this view it should be, reflexed and is continuous with that lining the sack. Ordinarily the penis lies coiled up in complicated folds, appearing like a large intestinal worm, and fills the lobed part of the peduncle, which apparently serves for no other purpose than its reception. In one case in which I dissected out the penis, I found it in its contracted state; 41/1000th of an inch in length, equal to that of the entire capitulum and peduncle; in a specimen, in which the penis had been naturally exserted, the part which protruded (m) was by itself rather longer than the whole animal; and as this specimen had been placed in spirits of wine, the organ no doubt was contracted; hence I think it probable that the probosciformed penis, when fully stretched out, would equal twice the length of the entire animal.

There must be a nervous system; and there must likewise be a gland (homologous with the ovaria) for secreting the cement; but I could not distinguish parts so small. Certainly there is no mouth, or stomach, or thorax, or limbs of any kind, or abdomen.

It is obvious that these males must be very short-lived: they perform their masculine functions and then perish. We have seen, however, that after the act of metamorphosis they do grow a little, and I have reason to suspect that this is effected, as with other Cirripedes, by moulting. The growth must be absolutely dependent on the store of nutriment laid up within the pupa. The young male, immediately after the exuviation of the integuments, thorax, natatory legs, abdomen, and eyes of the pupa, consists of a pulpy cellular mass, without any internal organs as yet formed.

Judging from the different sizes of the females which included perfectly developed ova, I infer that they must breed more than once during their lives; and therefore, that successive sets of males, as in the genus Scalpellum, must become attached to them. I was not, however, able to discover the prehensile antennæ or other remains of the old males adherent to the females; a circumstance which I presume is accounted for by their attachment being weak. Considering the very small size of the male, it is not surprising that so many,--in one case fourteen,--are required to impregnate the numerous ova of a single female. How the males know the proper period when the ova, lying in a sheet at the very base of the sack of the female, are ready for impregnation, I cannot say, without it be that they perceive the moulting of the external membrane, close to the edge of which they are attached; for this moulting would indicate the period when the ovigerous lamella came to the surface of the sack, and the ova would then be soon ready for impregnation. From the position in which the males are attached, and from the extraordinary length of the probosciformed penis, capable of voluntary movements, I have no doubt the males can insert the tip of this organ within the lower edge of the orifice of the sack, and there discharge the spermatozoa, which, by their own movements, must pass down the sides of the sack of the female till they reach their proper destination. The position of the males, with respect to the female's body, is almost exactly the same as that occupied by the complemental males of Scalpellum Peronii and villosum; the lower and narrow end of the fissure, worn in the gasteropod shell, here affording that protection to the males, which the edges of the opposed scuta afford to the complemental males of the above two species of Scalpellum. We cannot doubt that these latter males aid in the impregnation of the ova of the hermaphrodites, but they are not furnished with a very long penis, probably for the very reason that they are complemental males, and therefore not so absolutely necessary for the impregnation of the ova as are the males of Alcippe.

I have, in my former volume, expressed my astonishment at the extent to which abortion had been carried in the male Ibla; but it has been carried much further in the male Alcippe. In Ibla, the thorax is reduced to a mere flap, and only two pairs of cirri exist in a most useless and rudimentary state, but there is a well organised mouth, stomach, and anus. In the males of Scalpellum vulgare, ornatum, and rutilum there is no mouth or stomach, but there is a thorax with four pairs of minute, modified cirri, and a large abdominal lobe. Here, in the male Alcippe, all these negatives are united, we have no mouth, no stomach, no thorax, no cirri, no abdomen! The archetype crustacean consists of twenty-one segments; of these the seventeen anterior segments can be clearly made out in the archetype Cirripede: now, in the male Alcippe, the first three segments are largely developed, forming all that is externally visible, but the remaining fourteen segments are absolutely aborted, but in idea may be considered as forming the membranous depression whence the probosciformed penis springs; for this organ normally arises at the extremity of the seventeenth segment. To show the wonderful diversity of nature, even in the same sub-class, I may be permitted to remark, that whilst in Alcippe only the three anterior segments are developed, the fourteen succeeding segments being rudimentary, in Proteolepas (hereafter to be described) these fourteen segments are all largely developed, whilst the three anterior segments are quite aborted, being represented only by a thin envelope to the two threads by which this Cirripede is attached to the supporting object.[149]

[149] It may be worth stating, that in order to procure perfect specimens of the female and male Alcippe, pieces of the shell inhabited by them should be dissolved in weak acids.

ORDER II.--ABDOMINALIA.

Cirripedia, having a flask-shaped carapace; body consisting of one cephalic, seven thoracic, and three abdominal segments; the latter bearing three pairs of cirri; the thoracic segments without limbs; mouth with the labrum greatly produced, and capable of independent movements; œsophagus armed with teeth at its lower end: larva, firstly egg-like, without external limbs or an eye; lastly binocular, without thoracic legs, but with abdominal appendages.

I feel compelled to form an Order for the one genus and species, namely, Cryptophialus minutus, to be here described. We must, I conceive, attribute much greater value, in classification, to internal parts and organs, at least where such are not known to vary, than to external structure. Now in Cryptophialus, the body consists of eight segments, of which the first two are not developed in any cirripede hitherto described. Of the eight, the seven posterior or thoracic segments are quite free, or detached from the carapace, and do not bear any appendages; whereas in all the foregoing cirripedes of the order Thoracica there are (at least in the normal sex) six pairs of cirri; Alcippe alone must be excepted, in which there are only two pairs. Again, in the Thoracica there are no abdominal appendages, excepting the terminal or caudal, whereas in Cryptophialus the abdomen bears three pairs of biramous cirri. In the crest of the labrum, being produced into a special, lancet-formed organ, articulated at its base and capable of movement, and in the palpi projecting straight upwards, we have a great difference from all other cirripedes; and these organs, we have every reason to believe, possess a high classificatory importance. The œsophagus in Cryptophialus, where it enters the stomach, is armed with teeth and hairs, moved by muscles, forming a beautiful structure, of which we have not a trace in any other cirripede. Lastly, and perhaps most importantly of all, the metamorphosis is different; for the early larval stages are passed under an egg-like condition within the sack of the parent; and the pupa differs from the pupæ of all other cirripedes, in not having natatory thoracic limbs, and is therefore only able to crawl about by the aid of its great prehensile antennæ.

Thus far the evidence is decisive in favour of Cryptophialus being placed in a separate Order; but if we were to trust to the characters derived from the external covering or carapace,--and such characters are of high importance, as we may safely infer from the natural arrangement of the foregoing families which depends on the structure of the carapace,--we should place Cryptophialus close to Alcippe amongst the Lepadidæ. These genera agree in their burrowing habits,--in their attachment by a horny rostral disc,--in the external membrane being covered with triturating points,--in the spinose and notched orifice, with an external lateral bar on each side, and in the inner tunic of the sack being protected by hairs and spines. They agree to a considerable extent in shape, and in the peculiar arrangement of the muscles of the whole external covering of the animal: they agree, also, in their manner of growth, and in the sack extending down to their basal extremity. Some of these resemblances may possibly be analogical, and due to similarity of habits, and not to affinity; and we must attribute to mere similarity in function, a certain amount of resemblance in their labrums, for this part is essentially different in the two genera; and to the same cause, the resemblance between the brush formed by the two pairs of thoracic cirri and caudal appendages at the end of part of the thorax in Alcippe, with the three pairs of abdominal cirri at the end of the whole thorax in Cryptophialus. I allude to this latter resemblance, for it was owing to it, and to the similarity in the habits of Cryptophialus and Alcippe, that I stated, in the introduction to my former volume on the Lepadidæ, that the two genera would probably fall into the same order. In the structure of all the parts of the mouth and of the cirri, in the digestive organs and in the metamorphoses, Cryptophialus is not more closely related to Alcippe than to any other genus whatever amongst the Lepadidæ.

Nevertheless I am confirmed in the view that the external resemblances between these two genera are due to some real affinity, and are not merely analogical, by a very remarkable fact,--namely, that Alcippe and Cryptophialus are both bisexual, and have males, several in number, attached exactly in the same position, and which males are so closely similar that, considered by themselves, they might absolutely be almost classed as species of the same genus! For they agree in the absence of all internal organs and parts, excepting the single testis, vesicula seminalis, and immensely long probosciformed penis; and they agree, also in manner of growth, in the arrangement of the muscles, and even in shape. The whole case seems to me very singular, and, as far as my knowledge extends, unique: we have two animals, of which the females, if classed by their external parts (homologically consisting of the three anterior segments of the head), would be placed alongside each other in the same family; but when classed by the whole rest of their organisation, certainly must be ranked in distinct orders;[150] yet the males of these very same animals might almost stand in the same genus. If it be asked why the position of Cryptophialus in the system should not be determined by the male, instead of by the female, the answer would be that the male is here abnormal and rudimentary in its whole structure; and I believe systematists are agreed that less perfect parts (and therefore a less perfect whole) offer less valuable characters than the more perfect parts or whole. We see this conclusion plainly verified in the case of the hermaphrodite Scalpellum vulgare and Ibla quadrivalvis, for there can be no doubt where these species should be arranged, yet if we attempted to place them by their complemental males, we should utterly fail: exactly in the same manner, if Ibla Cumingii and Scalpellum ornatum were ranked by their males, they would be quite misplaced. So again, if we were to attempt to class the six species of Scalpellum by their males and complemental males, undoubtedly the first three and last three species of the genus would have to stand in distinct orders! Hence we may reject the males as a foundation for classification, but no doubt they serve to show that the resemblances in the carapaces of Alcippe and Cryptophialus, are not merely analogical or functional, but evince a true affinity, though these genera differ so greatly, in mouth, body, œsophagus, cirri, and especially in their metamorphoses.

[150] M. Milne Edwards would, perhaps, in accordance with the profound views lately propounded by him on classification, consider Cryptophialus as an extremely modified, and, to a certain extent, degraded member or satellite of the type of the Lepadidæ; but I do not myself feel able to draw a line of distinction between the being a very abnormal member of one group, and belonging to a distinct group. I may add that I have several times tried to persuade myself, with no success, into the belief that I have somehow misunderstood the homologies of the thoracic segments and cirri of Alcippe and Cryptophialus; for if this were so, the two genera could be brought into much closer relationship; but with any conceivable amount of error on my part, there remains the great difference in the metamorphosis, not to mention the palpable differences in the cirri, the parts of the mouth, and in the whole course of the alimentary canal.

CRYPTOPHIALUS MINUTUS. Pl. 23, 24, fig. 1 to 19.

Hab.--Chonos Archipelago, Southern Chile; imbedded in the Concholepas Peruviana.

FEMALE. Fig. 1-18.

General Appearance.[151]--This, the smallest known cirripede, is flask-shaped and compressed, with a small orifice, on a more or less produced neck, placed at one corner: one of the narrow sides of this carapace is somewhat flattened or depressed, with its superior edge prolonged a little upwards; by this side, the animal is attached to the cavity in the shell, within which it is lodged. There is here no distinction between a peduncle and capitulum, that is between the lower or anterior, and the upper or posterior end of the animal, as seen externally. The small orifice is toothed and hairy: it is coloured purple, as is likewise the projecting labrum; the rest of the animal being tinted only by the muscles and internal parts seen through the outer integuments. The largest specimen (fig. 2) which I have measured did not quite attain the length of one tenth of an inch. This cirripede inhabits, in vast numbers, the shells of the living Concholepas Peruviana, amongst the Chonos islands; the whole outside of the shell being sometimes completely drilled by its cavities, almost touching each other, as happens in the case of Alcippe with the shells of Buccinum. The oval aperture leading into the shell-cavity, in full-sized specimens, is between (2-3)/100 of an inch in length: it is generally surrounded by a narrow, internal, calcareous rim, which apparently has the same inorganic origin, as in Alcippe. The toothed orifice of the carapace leading into the sack, fills up the orifice of the shell-cavity; but it can be voluntarily withdrawn a little: when opened, and the animal is in action, the lancet-formed, moveable crest of the labrum, and the abdominal cirri, are exserted.

[151] I am greatly indebted to Dr. Hooker, for having several years ago, when I examined this my first cirripede, aided me in many ways, and shown me how to dissect the more difficult parts, and for having made for me several very correct drawings, which, with some subsequent alterations, are now engraved.

Integuments.--The external membrane is colourless, thin, but strong; it is studded with minute bifid, trifid, and quadrifid points of hard chitine, which are the agents of excavation: they are directed upwards, except towards the lower end, where they are directed from the disc or surface of attachment. These points beneath the orifice, and on each side close along the lateral bar, are larger than elsewhere. There are no points on the disc or surface of attachment, which is formed of somewhat thickened, yellowish membrane, and is not moulted, like the rest of the external membrane, but is formed of successive layers extending beyond each other; the lines of growth, however, being obscure, and only occasionally distinguishable. The disc is oval, not extending to the lower end of the animal, and with the upper edge thinning out and produced upwards (fig. 1). The animal, during its growth, moves a little downwards in its cavity, by means of the new layers of the attached disc being formed, not symmetrically with respect to the old layers, but beyond them or at a greater depth in the shell; hence when the animal is removed quite perfect, by the Concholepas being dissolved in acid, the upper and deserted margin of the disc or surface of attachment generally projects as a free edge, but in a tattered and worn condition. In full grown specimens, which have ceased burrowing downwards, nearly the whole disc, though occupying the same position relatively to the animal, becomes in fact deserted, and is lined by membrane continuous with, and like that, investing the rest of the body, but furnished only with simple blunt points, instead of with the sharp bifid and trifid triturating points.

The orifice is formed on each side by a toothed rim of hard chitine (fig. 3, 4), which can be opened and shut, owing to its being flexible at the rostral end, and folded inwards at the carinal or posterior end. The teeth vary in arrangement and sharpness: generally they form, taking a rim on one side (fig. 3), two prominences or groups of points at the rostral or anterior end, always separated by a broad notch, from the bottom of which the lateral bar extends downwards, from the posterior, larger and less regularly toothed half of the rim. Of these teeth the larger ones project nearly straight up, and the smaller and lower teeth outwards, graduating into the smaller teeth, just below the rim, which again graduate into the minute points, studded over the whole surface. These outer teeth probably serve to prevent any creature crawling into the cavity, between the shell and animal. Scattered bristles rise from all over the rim. The lateral bar, above alluded to, consists of the general membrane of the body, thickened, hardened, rendered elastic, coloured yellow, and apparently formed into a fold: where attached to the under side of the rim, at the above-mentioned notch, the bar is thinner and more flexible than elsewhere: it runs half way down the animal, first straight and then curved towards and closely approaching the disc or surface of attachment. At the lower end, the bar, or more strictly the thickened membranous margin of the bar (b′, fig. 3), expands into an oblong, slightly rigid plate, studded with from three or four to ten or twelve points, which have their ends expanded and truncated, or even slightly bifid. The extremity of this plate projects freely from the general surface of the body. We shall afterwards refer to the use of this extremely peculiar bar and plate.

The two rims forming the orifice cannot be quite closed; but ingress by any foreign object into the sack is beautifully prevented by an internal membranous lip on each side (d′, fig. 3, 4), and by a third inwardly folded lip (d′) at the posterior and broad end of the orifice. These three lips can be brought together, and form a valve. The lateral lips are very narrow at the mouth or rostral end of the orifice, where the hairy lancet-shaped crest of the labrum closes the orifice, and largely expand towards the posterior end: they are produced from the inner tunic of the sack: they appear formed of the finest hairs, placed parallel and approximate, but when examined under the highest powers, these hairs (for they still appear such) are found to be united by delicate membrane, which has its extreme edge fimbriated. The third, or posterior and inwardly folded lip, differs in being composed of much coarser, flattened hairs, which are united towards their bases, and are free at their extremities, where they are serrated or coarsely plumose on both sides.

The sack extends down to the lower end of the animal. It is lined by delicate membrane. At the orifice on each side, a little posteriorly to the lateral external bars, this inner membrane is strengthened by a pair of thin yellowish bars (c′, fig. 3), which run parallel to the straight portions of the external bars. These inner bars at their lower ends become pointed and die out: at their upper ends, and close to the rim, they are broader, but more flexible, and so transparent as hardly to be distinguished from the rest of the membrane. At the rostral end of the orifice, in a medial line, this same inner tunic of the sack is thickened for a short space downwards, so as to form a fifth bar (c′′); which separating from the inner tunic, runs inwards between the outer and inner membranes of the carapace (i. e. between b and c, fig. 3, 5), behind the mouth, as far down as opposite to the lower end of the œsophagus, and there becoming thinner and ligamentous, gives attachment to some powerful muscles.

At each exuviation, the external membrane with the dentated hardened orifice, the lateral bars, the inner tunic of the sack with its bars, are all moulted, together with the usual integuments of the animal's body. New and sharp triturating points are thus periodically formed for the work of excavation. The whole animal increases during growth in every direction, and therefore, at its lower or basal end, as was the case with Alcippe. The disc or surface of attachment, is added to by new underlying layers, extending beyond the old layers at the lower end and on the sides, but not at the upper end, where, as in the case of the calcareous discs of Lithotrya, the old layers are deserted and worn away. I saw what I believed to be little globules or patches of cement; but I was not able to discover any cement-ducts.

Muscles of Sack and Orifice.--The animal is surrounded by rather strong longitudinal muscles, not running up close to the orifice: these muscles exhibited, to my surprise, distinct traces of transverse striæ: there are no external transverse muscles, as in all the Lepadidæ. Attached to both sides of the inward fold or hinge, at the posterior end of the orifice, some striated or voluntary muscles run for a short distance downwards, diverging like a fan: their contraction would cause the dentated rim to open: a strictly homologous muscle occurs only in Alcippe. At the opposite end of the orifice, a remarkably powerful voluntary muscle is attached to the ligamentous bar above described as proceeding from the rostro-medial end of the toothed rim (c′′); and at its lower expanded end, it is attached under rather above the middle of the disc: this muscle corresponds with a similar one in Alcippe, and with some much weaker muscles in other Lepadidæ. Its action would be to draw down within the shell-cavity the whole dentated rim, and likewise to close the orifice; and here, I believe, come into use the lateral elastic horny bars with their curious basal projecting plates, furnished with expanded points, for much friction would thus be caused by, yet some play be allowed for, the several movements; the elasticity of the bar bringing up the dentated orifice, when the powerful muscles attached to the rostral end of the latter became relaxed. Round the space where the just-mentioned muscles are attached to the horny disc, a sheet of other muscles radiate, a few on both sides obliquely upwards, but the greater number transversely and within the first-described longitudinal muscles; they extend on both sides about half round the animal. There are similar muscles in Alcippe, but not extending so far round the animal. Their action must be to draw the whole carapace towards the surface of attachment; the action of the longitudinal muscles being to shorten it; the orifice supported by the lateral horny bars, serving as the fulcrum for the contraction of the longitudinal muscles. I could not see any adductor scutorum muscle, although I looked particularly under the expanded plates at the ends of the lateral external horny bars.

Body.--This is laterally compressed: it is widest and thickest at the upper end, and thence tapers to the lower or posterior end. The last three or four thoracic segments are bent under the anterior segments, giving the whole something of the appearance of certain crustaceans, divested of their legs. The somewhat conical mouth, with its singular labrum, is very large. The body consists of eight segments. The first segment (fig. 5, 1), or that succeeding the mouth, is the seventh or last cephalic segment of the archetype crustacean; it is the largest of all eight segments; it is joined by its dorsal surface to the carapace or external covering of the animal, and the membrane with which it is invested is prolonged upwards and downwards (c, c, fig. 5), and so forms the inner tunic of the sack. The succeeding seven segments are thoracic; they are free, and are destitute of limbs; the articulations separating them are transverse. The first and second thoracic segments give rise, on their medial dorsal surfaces, each to a remarkable tapering curved appendage, presently to be described. At the end of the last thoracic segment, there is a minute abdomen, bearing three pairs of biramous cirri.

The Mouth consists of three pairs of organs, namely, the outer maxillæ, maxillæ, mandibles with their palpi, and of a great and very curious labrum. These organs, by the fusion (as in other cirripedes) of their lower segments, form a large, somewhat conical, projecting mouth, which is separated on the ventral surface from the rest of the body by a distinct fold or articulation, where the muscles proceeding to the above gnathites are attached. The labrum (e, fig. 5, 9) is of large size; and the crest close over the opening of the œsophagus is produced into a great, lancet-shaped, moveable organ, wholly unlike anything occurring in any other cirripede: it is coloured purple, and is thickly fringed in the upper part by very fine hairs: it is bowed a little backwards from the mouth: the base, which rather overhangs the œsophagus, is a little contracted, and is transversely marked by an articulation: two small, parallel, voluntary muscles (with transverse striæ) are attached at their lower ends close beneath the articulation, and extend about one third up the organ: their contraction would serve to erect it; and their relaxation would, apparently, allow it to fall backwards on a little knob (e′, fig. 5) behind. This little knob resembles a similar projection in many of the Lepadidæ. As the labrum is formed of similar membrane with that of the succeeding segment of the body, its limit downward, beneath the knob, can be told only by a small apodeme which projects inwards, at a little distance within the line where the membrane of the body is reflexed upwards (c), so as to form the inner tunic of the sack.

The mandibles, palpi, and maxillæ, all project more than is usual. The Palpi (f, fig. 9, 5) are narrow, flattened, and taper a little; they support a few long bristles on their tips, and on one of their sides. In every other cirripede (in which the palpi are developed) they are directed transversely across the mouth, one towards the other, and are for a considerable space united to the labrum: here they project straight up, and seem to rise exteriorly to the bases of the mandibles; they are, however, united to the basal lateral edges of the labrum, and when the latter is torn from the rest of the mouth, the palpi separate with it. I could not distinguish the knob on which, in every other cirripede, the palpi are articulated. The Mandibles (fig. 8) have an upper, lower, and middle tooth, with some finer intermediate points and hairs. The Maxillæ (fig. 7) are narrowed in at their spinose edge, where there are three large spines and several finer bristles, together forming a flattened brush: this organ is remarkable from the apodeme (a) being bent into the shape of a scythe, with the terminal or blade-portion a little expanded, and directed backwards and inwards. The Outer maxillæ are sub-triangular in outline, with several bristles on their summits and along their outer surfaces.

Segments of Body.--I have stated that the mouth is succeeded by eight segments. As in all the cirripedes hitherto described, the body consists of only six segments, the number eight at first seems very improbable, and therefore I may be permitted to state that both Dr. Hooker and myself, when first examining this animal, and having no notion whatever regarding its homologies or the structure of other cirripedes, came to the conclusion, judging only from external appearances, that is, from the transverse folds, and from the lines of movement when the body was bent by a needle, that there were really eight segments. I have since carefully looked to this point: when the outer membrane is cleaned and examined, the four posterior segments are very plain, owing to a dorsal medial line, being alternately either thickened and coloured yellowish, or thin and colourless: the four anterior segments are less plain, but yet the membrane on the dorsal surface, on the line of each fold or articulation, does present some difference, from being destitute of the fine, transverse, toothed scales which occur on other parts. But I lay most stress on the fact, that all these eight articulations were used for the attachment of muscles. Hence I conclude that the eight segments are real; and we shall see, in the next order, that the very same eight segments are as plain in Proteolepas, as in the larva of an insect or as in an annelid. There is good reason to believe that the general covering or carapace consists in all cirripedes of the three anterior segments, and that the mouth (judging from its appendages) also consists of three segments, consequently the first segment of the body in Cryptophialus must be the seventh or last cephalic segment, and the seven next free segments must be the normal seven thoracic segments.

The first segment of the body (i. e. last cephalic, fig. 5, 1) is, as stated, the largest, and is attached dorsally to the carapace: its ventral surface is flattened, and is formed of somewhat thickened membrane: on each side, a little below the articulation separating this segment from the mouth, there is a small blunt projection, with the free part only 1/500th of an inch in length. Each of these appendages bears four or five bristles on one side near the summit, and a few on the other side, lower down: from their position I believe them to be rudiments of a first pair of maxillipeds (tetartognathites of Milne Edwards), of which no trace occurs in any other cirripede. The differences between this segment and the seven succeeding segments, is of interest, as offering some confirmation of the belief, lately disputed by some naturalists, that the cephalic and thoracic segments in the class Crustacea, do differ in their nature,--a conclusion which we shall see further confirmed under Proteolepas. The second and third (i. e. first and second thoracic) segments (2, 3, fig. 5) are the next largest, and are remarkable from supporting singular appendages, already alluded to. The sides of the second segment are formed of thickened yellowish membrane. The fifth and sixth segments are the smallest, and mark the point of chief flexure of the body. The eighth segment is a little elongated, formed of thicker membrane than the other segments, and dorsally is indented by the anus.

The singular tapering appendages (fig. 5, i, k) arising dorsally from the second and third segments, differ from each other only by the upper one being smaller, less curled, and perhaps rather smoother. When first examining this animal, not knowing that it was female, and not finding a probosciformed penis, I concluded that these organs were of this nature,--an excusable mistake, considering their almost ringed structure, their somewhat constricted bases, the direction of their curvature, and their position in the midst of the ova within the sack. On careful examination, however, these appendages are seen not to be truly ringed or articulated, but are covered with transverse lines of scales, hirsute on their edges; these scales being less distinct, or even quite absent on the smooth upper portion; they do not include any muscles; they are imperforate at the apex, which is not furnished with bristles (as seems always to be the case with the probosciformed penis); and, lastly, they are lined by corium, but are not occupied by any vessel, gland, or organ of any kind. The only function which I can assign to these appendages, is that of aiding the retention of the ova within the sack: for the ova, when first produced, are aggregated round them; at this period I several times observed long, somewhat curled, very thin fibres, not tapering like hairs, adhering to both appendages, the nature of which fibres I cannot explain. In very many cirripedes there seems a strong tendency to the production of tapering, filamentary appendages, somewhat like the two (i, k) here described,--namely, at the bottom of the sack in some Balaninæ, at the bases of the anterior cirri in Lepas and in some other genera, and on the dorsal surface of the prosoma in certain species of Pollicipes; in this latter case some of these appendages were covered by scales; and the prosoma whence they arose answers to the third segment of the body in Cryptophialus, or that supporting the lower and larger appendage. Appendages of this nature, in several cirripedes, serve for the lodgment of the testes, but in some cases they are of no apparent use, excepting, perhaps, in aiding respiration by the expansion of corium thus exposed, and this partially may be their function here, for there are no proper branchiæ.

Cirri.--There are three pairs, together forming a nearly straight brush, of considerable length, projecting in a line with the last thoracic segment. Each cirrus is biramous. In a moderately large specimen there were twenty segments in one of the longest rami. Each segment (fig. 14, a) is strengthened by a dorsal or posterior shield of thickened yellowish membrane, from the upper edge of which a single smooth spine projects; the anterior surface is likewise strengthened on the two edges by thickened membrane, and supports two pairs of long spines, which are plumose, or rather hirsute, on both sides. In the lower segments of both rami of the several cirri, the inner spine of each pair is considerably shorter than the outer spine,--evidently in relation to the little power of divergence of the two rami. All the cirri resemble each other, excepting that the rami of the anterior pair, are rather shorter than those of the other cirri, but the dorsal spines on their segments are longer. In all ordinary cirripedes the two rami are equally supported by the upper segment of the pedicel, which latter is very short compared with the lower segment, and is separated from it by a transverse articulation. Here (fig. 13) the exterior or anterior ramus is articulated on the pedicel, almost like a branch, in front of the other ramus, which seems more directly continuous with the pedicel. The upper segment of the latter is separated from the lower segment, both being of about the same size, by a very oblique articulation. On the front surfaces of the pedicels there are two or three pairs of spines.

Abdomen.--The three cirri on one side are separated from their opposite pairs by a prominent, longitudinal fold, formed of thickened yellowish membrane, which, when foreshortened by being viewed dorsally, looks like a style projecting immediately beneath the anus. The transverse folds separating the three pairs, are exceedingly slight. The inner basal edges of the pedicels of the cirri project slightly inwards as apodemes, giving, I believe, attachment to some muscles. The anus lies between the posterior pair of cirri, and deeply indents the last thoracic segment. The transverse folds separating the three pairs of cirri, little developed as they are, must, according to all analogy, be considered as representing three segments of the body, and as we have accounted for seven cephalic and seven thoracic segments, we must conclude that these are three abdominal segments. We know, moreover, that the abdomen in the pupæ of the Thoracica, with a single exception, does actually consist of three segments.

Movements of the Mouth, Thorax, and Cirri, &c.--Judging from the fact of the lancet-shaped appendage of the labrum being more or less exserted in dead specimens out of the shell-cavity, and from the analogy of other cirripedes, I do not doubt that the whole mouth can be considerably raised and depressed; we have seen, also, that the rostral end of the toothed orifice of the sack can be pulled down, which would aid in exposing the mouth and labrum. The well-articulated thorax, by the aid of the muscles attached to every segment, can certainly be doubled up and contracted, so that the cirri with their pedicels (coloured purple like the exposed labrum) can be wholly protruded out of the sack and shell-cavity. The three cirri no doubt can be separated a little from each other, both transversely and longitudinally; and according to analogy, the two rami of each cirrus can likewise be separated: there are, also, muscles for moving the two segments of the pedicel of each cirrus; and other muscles run up the many segments of the rami. We have seen that the great lancet-formed appendage of the labrum, laterally fringed with fine hairs, can be erected; and I do not doubt that the prey when entangled by the expanded cirri, is borne against this appendage, and is then, by the retraction of the thorax, dragged down its smooth surface to the mouth, where it is seized by the mandibles and maxillæ, which lie like a trap at the bottom of an inclined and moveable plane.

Alimentary Canal.--The œsophagus is long; it runs backwards from the mouth and then downwards; at its lower end, where it enters the stomach, the part, which in other cirripedes is expanded and bell-shaped, is modified in a most singular and quite peculiar manner; for the lower part of the œsophagus, after widening a little, becomes converted into what appears at first like a square box, 8/1000ths of an inch across. This box is really deeply folded (see diagram, Pl. 24, fig. 11) into six longitudinal ridges and hollows: two of these hollows, facing each other, are wider than the others, and when the organ is dissected out of the body, it generally lies (fig. 10) with one of these faces exactly over the other, the narrower lateral folds being thus hidden, and the whole consequently appearing like a simple square box with concave sides. But when a section is made, or the lower open end is turned upwards, we see that the organ is six-rayed and elongated, with the longer axis standing parallel to the flattened sides of the animal's body. The edges of the folds are formed of yellowish, thickened membrane, with a sinuous or beaded outline, which serve to strengthen the organ. Internally, the two broad concave sides are armed, in their upper inwardly prominent (fig. 12) part, each with a disc, 2/1000ths of an inch in diameter, crowded with short, thick, brownish, inwardly projecting teeth. The two discs stand exactly opposed to each other. The bases of the teeth, seen from the outside (Pl. 24, fig. 10), seem like brown little circles, with a smaller circle within. The disc obscurely appears to be formed by the confluence of two smaller discs which lie, I believe, at a very small angle to each other: beneath each of these half discs there is a longitudinal band of very fine hairs, the two bands uniting into one, lower down within the organ. The internal longitudinal edges, also, of the four lateral smaller folds are likewise clothed with fine hairs; hence we have six parallel longitudinal rows of very fine but stiff hairs, or eight, if the united bands on the two broader faces under the discs be counted each as two. These bands of hairs, and the opposed discs, armed with very strong teeth, can be separated and brought together with force, by the action of strong constrictor and diverging muscles. Hence any prey carried down the œsophagus, before entering the stomach, would have to pass, as it were through a mill, and be subjected to a severe trituration by the discs of teeth, and immediately beneath to a brushing by the six longitudinal bands of hairs. This curious and unique structure answers, I believe, the same purpose as the four convex, hardish, crenated buttons on the posterior thoracic cirri in Alcippe, which are likewise unique in that genus. I observed that in some specimens the teeth had been worn quite blunt, but the teeth and hairs are periodically moulted and renewed, together with the whole œsophagus.

The stomach is broadest at the upper end, and extends from a little beneath the mouth down to the fifth segment of the body, where it becomes narrow. It presented an irregularly contracted appearance, and was covered by a pulpy hepatic layer. The rectum is of rather large diameter; it extends from the middle of the fifth segment to the end of the eighth segment of the body, or seventh of the thorax, where the large anus is situated, lying between the posterior abdominal cirri, and partly hollowed out in this seventh segment. The rectum, as in all other cirripedes, is periodically moulted. The food is of a bright green colour, as if of a confervoid nature; the triturating and brushing action of the œsophagus seems to roll this matter into pellets, which apparently retain this form until finally expelled as excrement: certainly the excrement is in pellets, and I have several times seen pellets within the stomach.

Organs of Generation.--The specimens as yet described are exclusively female, there being certainly no testes or vesiculæ seminales. As in every specimen collected (early in January) there were within the sack either nearly mature eggs, or young larvæ, it was the worst period for seeing the ovarian cæca, and I have failed to discover them in the specimens now long kept in spirits of wine; but I cannot doubt they would be found, between the inner and outer tunics of the carapace or general covering, near the disc. I have stated in my original notes, made when the specimens were alive, that the ova are at first perfectly detached; but some appearances make me believe that I overlooked (as might easily happen) the often excessively fine membrane which in other cirripedes unites the ova together, and so forms the ovigerous lamellæ. The ova are much less numerous than in other genera, varying from only nineteen to about sixty. In the same individual all the eggs were always in the same state of development.

Metamorphoses.--The true ova, in their earliest condition, when in the sack, are ovate (Pl. 24, fig. 15), orange-coloured, quite smooth, and barely 10/1000th of an inch in their longer axes. They soon become broader at one end than at the other; and by degrees the narrow posterior pointed end becomes developed into a slightly club-shaped, almost transparent (fig. 16) horn, and the broader anterior end, into two rather longer horns. The length of the oval part, not measuring the horns, is nearly the same as in the primary true egg condition. There is as yet no trace of internal organs, the whole contents consisting of pulpy granular matter. How far the above changes are effected by moulting, either of the whole or of part of the integuments of the egg-like body, I cannot say; but the pulpy matter within the ovum, even in its earliest stage, was included within an inner envelope or case.

In the next distinct stage (there being, however, slighter intermediate changes) the posterior horn has shrunk, and become converted into a bluntly-pointed conical termination for the whole body (fig. 17), whereas the two anterior horns have approached each other on the future ventral surface, and have increased considerably in length and thickness, and contain within them the prehensile antennæ, which can be externally seen, and which I dissected out of these horn-like cases. The oval part of the egg-like larva (for I hardly know what to call it) is now very slightly shrunk, being hardly more than 9/1000ths of an inch in length. At this stage, these bodies adhere by the tips of their anterior horns, containing the antennæ in process of formation, to the inner tunic of the sack, and likewise in little groups one to another: as the included prehensile antennæ ultimately become attached by cement (proceeding, no doubt, as usual, from a modified portion of the ovarian tubes), it seems probable that some cement may at this early period be excreted, but I could not make out the exact means of attachment. The egg-like larvæ are, also, aggregated round the tapering curled dorsal appendages of the second and third segments of the body, and it is possible that at this, or at an earlier period, these appendages may act like the ovigerous fræna in the Lepadidæ, and serve to retain the egg-like larvæ within the sack.

We come now to the last larval, or pupal condition, before the final metamorphosis into the mature animal; the changes above described have been, at least to a great degree, if not absolutely gradual; but the pupa suddenly appears perfectly developed, from the moulting of the last-described horned, egg-like larva. It is now a free animal crawling about the sack of its female parent. It has increased a little in length, as compared with the oval part of the egg-like larva in its second stage, namely, from a little above 9/1000ths to 16/1000ths of an inch: from the position of the prehensile antennæ in the two states, I have no doubt that this increase of size is entirely due to the anterior part of the pupa being doubled up whilst within the egg-like larval envelope. The pupa in shape (fig. 18) somewhat resembles a coffin, and is far less laterally compressed than other pupæ, and hence can easily be placed either on its dorsal or ventral surface. The prehensile antennæ are of large size: when the animal was alive, they were concealed under and partially included within, the front part of the carapace or shell, which in this condition was not so much truncated as in the drawing given (fig. 18) of a specimen lying on its back, with its antennæ protruded. Some specimens formerly examined for me by Dr. Hooker, had their antennæ and whole ventral surface forced outwards, apparently from the endosmose of the spirits of wine. The whole dorsal surface, and the overlapping sides of the carapace are elegantly punctured, and are formed of a rather brittle substance, here and there supporting, especially at the front end, some fine and rather long bristles,--which latter I have not seen on the pupæ of other cirripedes. The ventral surface is very narrow towards the posterior end of the animal; it is formed of thin, structureless membrane. On this surface, close to the posterior end, there is a minute orifice, through which three pairs of bristles are protruded, attached to (as I believe) the rudimentary abdomen; the bristles apparently cannot be withdrawn.

The antennæ, (fig. 18) as stated, are of large size compared to the whole animal: they resemble, in all essential respects, the same organ in other cirripedes. The ultimate segment is unusually thick;[152] it is terminated by five bristles, one of which is longer than the others, and stands rather separated from them. The disc-segment is large, nearly circular, with the broad edges transparent and membranous; on its posterior edge there is a single small spine. The second or main segment, counting from the base, has a single spine on its upper margin, close beneath the spine on the disc; it is articulated to the disc-segment, a little way from the disc itself,--which is a peculiarity I have not elsewhere noticed. The basal segment is thick and not so short as usual. These organs are furnished with powerful muscles. They are generally protruded alternately; and by the adhesion of the sucker-like disc, the animal drags itself along. The sucker-disc has great play, and when observing specimens alive, I compared its action to that of a wrist-joint. The antennæ, when retracted within the carapace, lie parallel to each other.

[152] As I have given, in my former volume on the Lepadidæ, p. 286, so many measurements of the antennæ, I may here add those of Cryptophialus,--the length from the end of the disc to the end of the second segment, (formerly called by me, erroneously, the basal,) is 26/6000ths of an inch; the greatest width of the second segment, 9/6000ths; the length of the little ultimate segment, 3/6000ths, and its width under 3/20000ths of an inch.

Posteriorly to the antenna, I distinctly saw the apodemes to which the eyes are attached: I was not able to distinguish any middle fork to the apodeme, which consequently does not resemble a UU, but U. The eyes are dark purple, and, as usual, compound: in one specimen I counted twelve ocelli within the common spherical envelope.

I could not distinguish any thorax, and certainly there is no mouth; nor, from analogy, could the latter be expected, excepting as forming part of the young cirripede: there are no natatory legs, which the pupæ in all other cirripedes possess. Of the three postero-ventral pairs of bristles, the most posterior or dorsal pair, differs from the other two pairs in being considerably smaller, and in being mounted on elongated pedicels: the two anterior pairs of bristles are strong: the three pairs are articulated, one behind the other, on a small body, apparently enclosed in a minute sack, and certainly attached all round by membrane to the internal edges of the orifice, through which the bristles are protruded. These bristles, when the pupa was alive, were often moved, and served apparently to steady the body during the alternate protraction and retraction of the prehensile antennæ. From the fact of the pupa of other cirripedes having an abdomen, formed of three segments, placed exactly in the same position as the minute body here supporting the three pairs of spines, I believe this body to be the abdomen. In other cirripedes only the posterior segment of the abdomen bears spines, which are supported on little limbs or pedicels, namely, the caudal appendages, the other segments being naked. But as the mature Cryptophialus, unlike other cirripedes, has abdominal cirri, the presence of spines on the corresponding abdominal segments in the pupa, is explained and rendered probable: there can, I think, be little doubt that the small terminal pair of spines, supported on elongated pedicels or limbs, answers to the caudal appendages found in many cirripedes.

The whole course of the metamorphosis is very peculiar. The gradual changes in the egg-like larvæ (for I suppose they must be called larvæ) from a simple oval egg, to pointed oval, to oval with three horns, and lastly to oval with the two anterior horns larger, and the posterior horn reduced to a mere point, seems to me very curious; and offers, as far as I know, a unique case. It is interesting to reflect how perfect a series, in the development of an animal, we have, in different members of the Articulata,--from an ordinary egg, in which all the changes go on unperceived, and whence a perfect animal is matured,--to an egg-like larva which undergoes the changes just described, and which turns into a pupa that does not eat or increase in size,--to a larva which eats and increases in size, but undergoes only one great change, as in most insects,--to a larva undergoing several great changes, as in the case of ordinary cirripedes, before its final metamorphosis into the mature animal. The first larval condition of other cirripedes, in which there is a single eye, three pairs of thoracic limbs, and a much elongated pointed body, covered by a prolongation of the carapace, is here not fully developed or matured; but this stage is, I think, clearly and very curiously indicated by the posterior horn of the egg-like larva, which we may suppose represents the posterior pointed end of the body, for it disappears in the succeeding stage, just as it does in the second larval condition of other cirripedes. In the first stage of ordinary cirripedial larvæ, the anterior horns are always present, serving, as in the case of these egg-like bodies, to enclose and protect the antennæ during their formation. The second egg-like stage answers to the second larval condition of ordinary cirripedes, as described (and figured, Pl. 30, fig. 1) in the introduction to the Balanidæ. The third or pupal state is fully developed in all cases.

Finally, the pupa of Cryptophialus is peculiar in its punctured, hairy surface, and in its shape, which, in being so much more depressed than usual, retains an earlier larval condition; but its chief and highly remarkable character consists in the entire absence of natatory legs; and, in consequence, instead of there being a large sack within the carapace, with an elongated orifice on the ventral surface, there is only a quite minute orifice at the extreme posterior end of the animal, through which the bristles, borne apparently on all three segments of the minute abdomen, are protruded.

The pupæ of the male and female are exactly alike in all their general characters, and probably in every point of detail; but my later and more minute observations were made only on pupæ, which, from their place of attachment, would certainly have turned into males. As these pupæ, without any further metamorphosis, were developed into males, we may, I think, safely infer that such is the case with the females: and, consequently, that the whole course of the metamorphosis has been, in this cirripede, seen and described. During this whole course, no food could possibly have been obtained, for the pupa is destitute of a mouth or organs of prehension, and the stock of cellular matter, enclosed within the ovum, has been sufficient for all the above changes, and for the final metamorphosis. We shall, moreover, immediately see, in the case of the male, that the stock of cellular matter has also sufficed for the development of testes, spermatozoa, and a wonderfully elongated probosciformed penis.

MALE. Pl. 24, fig. 19.

By throwing pieces of the perforated shell of a Concholepas into acid, I examined several scores of specimens of the Cryptophialus, and on all, with the exception of a few young individuals, males were attached. They were attached by cement, proceeding in the usual manner from the prehensile antennæ, outside, to the edges of the upper half of the disc formed of the thicker not-moulted membrane, by which the female adheres in her chamber: hence the males are included in the upper part of the same cavity with the female, into which they must have crawled as pupæ. I found from one or two up, in one case, to seven males, attached to the same female; four or five being the most usual number. In the early part of January, when all my specimens were taken, many of the males had not shed their pupal integuments, and of those that had, the majority were immature, a few only having spermatozoa: all the females had within their sacks, either ova including almost perfect pupæ, or fully developed pupæ: we may, consequently, conclude that these young males were maturing in order to impregnate the next set of eggs.

The male, immediately after its metamorphosis from its pupal condition, which has been fully described, is almost globular, but slightly bilobed, and is formed of strong, structureless, transparent membrane, including a mass of cellular matter, apparently without any included organs: it is attached by about the middle, between the anterior and posterior lobes, by the not-moulted prehensile antennæ. When the male is mature, its greatest length, measured from the posterior end, where the orifice is seated, to the anterior and blunter end, is about 13/1000 of an inch, and therefore rather less than the pupa, which was 16/1000ths in length. Relatively to a full grown female, the male slightly exceeds half the diameter of the toothed orifice leading into her sack, see (z) fig. 1, Pl. 23. In the mature condition, (fig. 19), one lobe, namely, the upper or posterior, has become more pointed, and is terminated by a minute orifice, 8/6000ths of an inch in diameter. This orifice is formed by a rim of thickened brownish membrane, which, on what was the ventral surface, has a few very minute, but strong, sometimes bifid spines;--in this one character, the male resembling the female. The other and lower (homologically anterior) end or lobe is broader, and contains a mass of cellular matter, which, from its close resemblance in appearance and position to similar matter within the male Alcippe, I have no doubt forms the contents of the testis. In one single specimen, I succeeded in isolating a vesicula seminalis of small size, containing perfectly distinct spermatozoa. Across the middle, between the two lobes, close under the outer integument, there is a broad layer of rather strong transverse muscular fasciæ. I did not observe any eye, the presence of which I should have expected from analogy. Internally there is no mouth, thorax, cirri, or other organs, excepting the testis and vesicula seminalis just mentioned, and an immensely elongated probosciformed penis, coiled up and filling the rest of the inside of the sack down to the testis, which latter occupies the whole anterior, and generally lower end of the animal. This penis is plainly articulated, and includes fine transversely-striated muscles: no doubt it can be protruded through the minute orifice, and voluntarily moved about. Out of a male, 12/1000ths of an inch in length, I dissected a penis, which, when not stretched, measured 50/1000ths of an inch in length; when a portion was pulled between two needles, it could be stretched to apparently three times its former length, and I should think that this organ could be extended by the animal to, perhaps, even the 100/1000ths of an inch,--that is, to between eight and nine times its own entire length! The use of this enormously elongated penis obviously is, that the spermatozoa of these males, which are so extremely small in size, compared to the female, should all be conveyed within the sack, and none be lost. It should be borne in mind, that the whole male, including every part, is scarcely larger than a single ovum, of which sometimes sixty have to be impregnated by only two or three males. In a full-grown female, the distance from one of the attached males to the middle of the orifice leading into the sack, is about the 5/100ths of an inch, equal to the length of the coiled up, not-extended penis: the further distance from the orifice of the sack to an ovum lying at the bottom of the sack, would be almost 10/100ths of an inch, so that the spermatozoa have to pass a distance of 15/100ths of an inch from the testis of the male to the lower ova. I believe two thirds of this distance would be passed safely along the probosciformed penis.

The resemblance between the male of Cryptophialus and of Alcippe is truly surprising; and is the more wonderful, considering the great dissimilarity of their pupæ. Hardly any characters can be pointed out in which these males differ, excepting such as might have been thought of only specific value, namely the relative proportions of the different parts, and mere external shape. The peduncle growing a little after the metamorphosis, in the male of Alcippe, and the prolongation of its capitulum with the included oblique ligamentous fibres, are the greatest differences. Having fully remarked, under Alcippe, on the wonderfully rudimentary condition of these males, destitute as they are of so many parts and organs, I will here say nothing further on these singular creatures, destined to discharge their spermatozoa, die, and be succeeded by a fresh set of short-lived male successors.

Order III.--APODA.

Cirripedia, with the carapace reduced to two separate threads, serving for attachment: body consisting of one cephalic, seven thoracic, and three abdominal segments, all destitute of cirri. Mouth suctorial, with the mandibles and maxillæ placed back to back, enclosed in a hood, formed by the union of the labrum and palpi. Metamorphoses unknown.

The characters above given fully justify, I think, the formation of this order; though it contains only one species, the Proteolepas bivincta. The mere external appearance (Pl. 25, fig. 7), so wonderfully different from that of every other cirripede, would by itself prompt to this same conclusion. At first sight the Proteolepas, if of fresh-water origin, might even have been mistaken for the larva of some insect, fastened by two threads to its prey. The entire absence of the three anterior segments of the head and therefore of the carapace, or, speaking strictly, the mere rudiment of these parts, forming an envelope to the two cement-ducts,--the absence of a stomach, rectum, and anus,--the entire absence of thoracic and abdominal appendages or cirri,--the absence of a probosciformed penis,--are all negative characters, which might ensue from degradation, so common with parasites; and which might, therefore, have been esteemed of not high classificatory value. But the suctorial mouth, with the palpi and labrum united into a hood, and with the mandibles and maxillæ reversed or turned back to back, so as to be utterly incapable of prehension, is a type of structure not hitherto met with, I believe, in any other animal, and cannot be explained away by degradation. The formation of the ova within the segments of the body, a peculiarity confined to this one cirripede, evidently results from the non-development of the anterior part of the head, within which the ova are usually formed; but the compound structure of the vesicula seminalis is a peculiarity which cannot be thus explained. Proteolepas has no particular affinity to any other cirripede; it resembles, indeed, Cryptophialus in one important point, but only in one point, namely, in the number of the segments of its body. It is really beautiful to see how the homologies of the archetype cirripede, as deduced from the metamorphoses of other cirripedes, are plainly illustrated during the maturity of this degraded creature, and are demonstrated to be identical with those of the archetype Crustacean. I was at first inclined to rank Proteolepas in one division, and all other cirripedes in another division of equal value; but as it may be inferred from the characters of the prehensile antennæ, that the pupa did not differ much, if at all in any important character, from the pupæ of other cirripedes, I have thought the three orders, which I have instituted, would be the most natural arrangement. As any one looking at the drawing given of Proteolepas, might very naturally feel inclined to protest against its being ranked as a cirripede, I must reurge the importance of the pupal antennæ being constituted on the common type, for from their structure, by the law of correlation, that of the whole pupa may be inferred; and even still more I must insist on the importance of the one great character of the antennæ being cemented to the surface of attachment by matter proceeding, as we shall see, in a modified state, from the great ovarian sack. The structure, also, of the mouth (to a certain extent), the segmentation of the body, though in appearance so peculiar, the hermaphrodite condition, the single penis, the absence of oviducts, all accord with, and taken together demonstrate, its cirripedial nature.

PROTEOLEPAS BIVINCTA. Pl. 24, 25, figs. 1-7.

Hab.--Parasitic within the sack of the Alepas cornuta, from St. Vincent's, West Indies, Brit. Mus.

General Appearance.[153]--The entire animal, as already remarked, curiously resembles, at the first glance, the larva of some insect. It is rounded, but somewhat compressed, and tapers gently towards the posterior end. It lies curved in an arc, the ventral surface being concave, and the dorsal convex, but a little flattened dorsally at the anterior and blunter end. Its length, if straightened, would rather exceed one fifth of an inch. The body consists of eleven segments, which, excepting the three terminal, are conspicuously plain. The first segment is surmounted by a rather small mouth, which any one would, assuredly, at first consider as the entire head, though he would in vain search here for eyes, antennæ, or other parts of the three anterior cephalic segments. On the dorsal surface, low down on the second segment of the body, two, quite flexible, thin, but strong, flattened threads arise, which terminate in a pair of prehensile antennæ, having the usual cirripedial structure. From the penultimate or disc segment of these antennæ, cement has been excreted, by which the antennæ are firmly cemented low down to the rostral end of the sack of the cirripede, the Alepas cornuta, on which it is parasitic: hence Proteolepas lies with its back downwards, and with its ventral concave surface fitting the convex body of the Alepas: its mouth lies under the middle of the soft prosoma of the latter cirripede, which I cannot doubt that it lacerates and sucks.

[153] I may be permitted to premise, that though I procured only a single specimen, yet perceiving its very singular nature, I took such care and length of time in the dissection, and repeated every observation so many times that I think reliance may be placed on the description here given. Fortunately I had acquired, from dissecting many much smaller specimens of various cirripedes, all the advantage which full experience could give me, when I commenced on Proteolepas.

Mouth.--The mouth is suctorial, and is constructed on a different plan from that in any other cirripede, or, indeed, in any other, as far as I know, articulated animal. It is narrower, in both a longitudinal and transverse plane, than the first segment of the body, and is distinctly separated from it. The lower part on the ventral side, is protuberant and rounded. The summit is square, and is formed by the crest of the labrum, with two large palpi (d, fig. 3), having nearly the usual form amongst the Balaninæ, and pointing towards each other, but differently from in any other Cirripede, they are united for their whole length to the labrum, and by their extremities to each other. These parts together thus form an arch or hood, within which stand the other gnathites. The palpi are roughened by groups of very minute spines. At their bases they can be obscurely seen to be separated from the rest of the mouth by an oblique joining or articulation. The back of the mouth is formed entirely of the labrum, which becomes narrow towards its base: it is, from top to bottom, 20/1000ths of an inch in height. Within the hood formed by the palpi and labrum, a pair (c, fig. 3), of very singular, compounded, mandibular organs project freely, straight up, with their convex outer edges placed parallel and close together, and their teeth pointing directly from each other, so that they stand in a reversed position compared with the jaws of all other cirripedes, and are absolutely incapable of prehension.

This compounded organ is singularly small compared with the palpi and labrum: it is narrow, being about 5/3000ths of an inch in width, but is produced upwards, so that a considerable length projects freely, and the rounded, properly external, margin can be traced down for a length of about 20/3000ths of an inch. In a lateral view of the mouth, the extreme tip of the mandibular organ could sometimes be seen just projecting out of the hood. The mandibular organ, when separated and carefully examined, presents the appearance, represented from a camera drawing, in (Pl. 24, fig. 2): we here see three groups of teeth; of these the lower set (c) consists of blunter teeth, placed more transversely, and easily separated from the others, and altogether clearly appears like a distinct organ. I do not feel nearly so sure regarding the other two sets; my first impression was strongly that they were distinct organs, closely united laterally together,--one (a) probably representing the mandibles, and formed into a single large tooth; the other (b) formed of three teeth, and probably representing the outer maxillæ; the first-mentioned set of teeth, which seemed to me to arise from between the other two sets, being the inner maxillæ. If this view (and it must be remembered how excessively minute the parts are) be not, as I now suspect, correct, we must suppose that the outer maxillæ are aborted, and we have seen some tendency towards this in other cirripedes; the compounded organ being formed only of the mandibles (having on this view four teeth) and the inner maxillæ. As far as the mandibles are concerned, their existence, I may remark, is plainly shown by the presence of the palpi, which in all cases belong to and form part of the mandibles. The ventral surface of the mouth, immediately beneath the free portion of the compounded mandibular organ, consists of a triangular projection, but I could see no appearances to make me suppose that this part represented the outer maxillæ. The compound organ--in general shape, and in the oblique manner in which the front part is cut off and terminates in ligamentous apodemes, to which muscles are attached,--presents an unmistakable likeness to a mandible. It is hollow within, and muscles appear to extend some way up, perhaps to the transversely toothed portion, which represents, as I believe, the inner maxillæ: these two groups of teeth, anyhow, seemed to have some power of sliding over each other, and altered their positions during the course of dissection. On each side of the mouth, there is a muscle attached by its lower end to the basal edge of the labrum, and two others, one above the other, attached by their lower ends to about the middle of the labrum; these muscles, which are distinctly striated or voluntary, I infer, from analogy, run up to the ligamentous apodemes of the compound mandibles. There appeared to be other more delicate muscles attached to the basal articulation of the mouth on the ventral face, and these, I presume, would run to the supposed inner maxillæ.

The mouth in forming a prominence separated by a distinct articulation from the body, and in the union of the palpi and labrum (though here carried to excess), is constructed so far on the cirripedial type; but how are we to account for the extraordinary reversed position of the united mandibles and maxillæ, with their backs almost touching each other, and their toothed edges twisted round so as to face outwards in a manner unexampled, I believe, in any other articulate animal? It might, perhaps, be at first suspected, that the compounded mandible had not really been twisted round, but that the teeth had been abnormally developed on the outer convex margin: this view, however, certainly cannot be admitted, for the properly outer convex margin can be traced running far down the mouth, in a manner utterly inexplicable, if this were really the inner side; and equally inexplicable on this view would be the position of the ligamentous apodemes. Hence I cannot doubt that this compounded mandibular organ has really rotated on its axis; and if the course of development could be followed, I suspect that the twisting would be seen to be effected as follows: we know in all cirripedes that the outer and inner maxillæ, and to a certain extent the mandibles, instead of facing each other, are directed towards the labrum; they therefore have already been twisted round a quarter of a circle, as may be seen in the diagram (Pl. 24, fig. 4), copied from the mouth of Ibla. Now let us drive inwards the front of the mouth, along a narrow medial line; these organs would then (fig. 5) be compelled to turn round a quarter of a circle more, and so face directly outwards. In this process, the integument between the lower and outer part of the mandible and the base of the palpus, which normally are in close contact, would have to be greatly stretched. By a movement of this order, the mandibles would come to stand posteriorly or exteriorly to the other gnathites; and as far as I could make out (previously to my having any theory) the large single toothed portion of the compound organ which most resembles a mandible, did really stand outside the other toothed portion.

With respect to the action of this singularly constructed mouth; if its ventral and oblique surface were applied to any yielding object, as the adjoining soft prosoma of the Alepas, the compound mandibles would be worked within an absolutely closed chamber. The action of these mandibles would be to make a transverse slit, and subsequently to serve as a grapnel to keep the mouth closely adpressed to its prey: the other teeth might act in keeping the wound open. When the mouth was thus closely adpressed over a wound, the great power of shortening the whole body which the animal possesses (the œsophagus being closed), would, by the subsequent action of the elasticity of the outer membrane, almost certainly create suction, and thus cause the nutritious juices of the Alepas to flow into the body of the parasite. Hence I have called the mouth suctorial.

Body.--This, as already stated, consists of eleven segments, of which the three posterior (abdominal) smaller segments can hardly be distinguished, without dissection, as separate from each other. The body is mainly occupied by a vast ovarian sack (e, e, fig. 7), filled by innumerable ova: and the three posterior segments by small testes and their vesiculæ seminales (i): but I shall return to the internal anatomy. The outer membrane, lined by delicate corium, is thin, transparent, elastic, and covered by groups of excessively minute blunt little points. The segments can be plainly distinguished by their outlines, especially on the ventral surface; but they are rendered unmistakably distinct by the attachment of the muscles; they can also be perceived when the external membrane is perfectly cleaned, by yellowish lines. The muscular system is highly symmetrical and simple: along all eleven segments, there is a narrow, medial, ventral and dorsal clear space; on both sides of which space there is a band of longitudinal muscles, which, though encroaching on the two sides, and rather largely on the dorso-lateral sides, may be called the ventral and dorsal muscles. These muscles are striæ-less, which is the case with the homologous posterior thoracic muscles in some other cirripedes: on the dorsal surface (lower surface in fig. 7) they are more spread out, and consist, on each side of the medial line, of four ribbons: this seems to be the case on the ventral side, but the ribbons are here much more confluent: in the seventh and eighth segments, the ribbons become broader; but in the ninth, tenth, and eleventh, or three posterior segments, they become much narrower, and some of the fasciæ disappear, so that these muscles can hardly be seen from the outside. Each separate ribbon expands a little at its two ends, which are attached to the articulations separating the successive segments: I carefully observed that they did not pass over at either end to the adjoining segments: hence their action must be either simply to shorten and arch each segment separately; or when acting together, to shorten the whole body, or perhaps the ventral or dorsal surface by itself.

In the first segment, and in the three posterior segments, these longitudinal muscles alone occur; but on the seven segments, from the second to the eighth inclusive, there are other oblique latero-ventral muscles. These muscles lie within the longitudinal muscles, and adhere pretty firmly to the coat (e, e, fig. 7) of the great ovarian sack. At their ventral extremities they are attached, near the anterior margin of each segment, beneath the point of attachment of the longitudinal fasciæ, and thence they run posteriorly in an oblique line to the anterior margin of the next succeeding segment, where they are attached: so that these muscles run obliquely from segment to segment. The first of these oblique muscles, lying chiefly within the second segment of the body, is thinner and longer than the others: those within the third and fourth segments are short: those within the fifth and succeeding segments extend, at their dorsal (or lower in fig. 7) extremities, as far as the outer dorsal longitudinal fasciæ: those within the seventh segment are broad and short, and cross the longitudinal muscles at only a small angle. In the eighth segment, there is an oblique lateral muscle, like that in the seventh segment, running from the ventral surface towards the dorsal surface; but there is in addition a second oblique lateral muscle, rising from the dorsal surface, and running towards the ventral surface. This muscle does not occur in the other segments, but in the fourth segment, at the dorsal end of the oblique latero-ventral muscle, there may be seen a small branch of fibres, at right angles, which seems to represent a muscle homologous with that just mentioned in the eighth segment: obscure traces, moreover, of similar fibres, can be detected in some of the other segments: had these oblique latero-dorsal muscles been as fully developed in the seven anterior segments of the body, as on the eighth segment, the whole muscular system would have been perfectly symmetrical. The oblique latero-ventral muscle in the sixth segment is distinctly striated transversely; but this is not the case with most of the other muscles, if with any of them; I cannot account for this difference. The muscles of the gnathites are the only other voluntary muscles in the animal's body.

Homologies of the Body.--It will hereafter be, I think, clearly shown, that when the shell and integuments of the pupa of Proteolepas are shed, no carapace or general covering for the body is formed; the three anterior segments of the head, the backward prolongation of which (as has been elsewhere explained) certainly forms the carapace of ordinary cirripedes, being here almost absolutely aborted. In every cirripede the mouth is formed of three pairs of gnathites, which, no one will doubt, rise from the fourth, fifth, and sixth segments of the head: here in Proteolepas, the mouth, even on the view of the mandibular organ on each side being compounded of only two gnathites, sufficiently resembles the ordinary cirripedial type to make it very probable, that if examined in the earliest stage of its development, three pairs of gnathites would be discovered. In accordance with this conclusion, the segment succeeding the mouth (i. e., the first segment of the body in fig. 7) homologically is the seventh, or last cephalic segment. The succeeding seven segments, of course, are the seven thoracic segments, and the three posterior segments are abdominal; the latter are not developed in ordinary cirripedes when mature, but are present during their pupal condition. Now this conclusion, which is, in fact, deduced from what we know of the front part of the head in other cirripedes, both larval and mature, appears to me most satisfactorily confirmed by the differences in the muscular system of the segments in Proteolepas. In no other way, I believe, can it be explained, why the last cephalic segment and the three abdominal segments should differ from the seven thoracic segments, in the entire absence of the oblique lateral muscles. The abdominal segments, moreover, differ a little in shape, in the indistinctness of their articulation, in the thinness of the longitudinal muscles, and even in their contents. With respect to the two threads enclosing the cement-ducts, which spring from the second segment of the body (or first of the thorax), and which terminate within the prehensile antennæ of the pupa, we shall hereafter see that their apparently most anomalous position, and even the flattened shape of the dorsal surface of the two anterior segments of the body, all accord perfectly with the homologies just given.

Alimentary Canal.--The œsophagus is thin, and for a cirripede short, for it extends only half-way down the first segment (i. e. last cephalic) of the body; the lower end, which is slightly dilated, nearly touches the anterior end of the great ovarian sack. At its upper end, it is surrounded by delicate, striæ-less constrictor muscles; and there are others radiating outwards, evidently serving to open it: the lower part of the œsophagus, differently from other cirripedes, is destitute of muscles, and is only coated by a thin layer of corium, which would serve to produce a new œsophagus at each exuviation. Strange as the fact may be, I am prepared to assert that there is no stomach, rectum, or anus. As I was able to trace so distinctly the œsophagus, and likewise the generally far smaller orifice and ducts of the male generative organs, I consider it quite impossible that I could have missed the stomach. The rectum and anus are absent in Alcippe: and the absence of a stomach is here in some degree the less surprising, as the structure of the mouth shows that Proteolepas must live on the already elaborated fluids of the Alepas, to which, being a cirripede, it is allied. It is of some importance to observe, that the œsophagus is fitted with muscles simply for shutting and opening it, the wave-like swallowing action of which other cirripedes are capable, being, apparently, here impossible; but the contraction of the body and its subsequent expansion, the œsophagus being opened, would allow the blood of its prey to flow inwards.

The nervous system must be much atrophied, for I could not detect it, and the small size of the animal is not sufficient to account for this: I wish I could have seen this system, for then I should almost certainly have beheld an articulate animal without a trace of a supra-œsophageal ganglion. There is no eye, but such could hardly be expected, as the anterior cephalic segments are aborted. There are no branchiæ. I may state that within the abdomen, along the dorsal surface, there was either a lacuna or a delicate vessel, apparently of a circulatory nature, of considerable diameter, which, near the extreme posterior end of the body, gave out branches.

Female Reproductive Organs.--The eight anterior segments of the body, with the exception of a small space at the two ends, are occupied by an immense (e, e), opaque, ovarian sack. The tissue forming it is delicate, and presents a peculiar cellular aspect: it is slightly attached to the corium on the ventral surface of the body, and to the oblique latero-ventral muscles. Internally, at the anterior end, it is thickly coated by cellular matter, the cells varying from 4/6000ths to less than 1/6000th of an inch in diameter, becoming in parts confluent, and the whole forming a dark orange-coloured mass. In the more central parts of the sack this cellular matter became aggregated into little pellets, which, in proceeding towards the posterior end of the sack, gradually increased in size, from about (4 to 6)/1000ths of an inch in diameter, and at last appeared as almost mature and perfect ova of a broadly oval figure. Their size, as we see, is small, and their number almost infinite. I carefully examined all round this ovarian sack, and could detect no oviducts; nor from analogy could they be expected: I have no doubt that the ova burst forth by the rupture, probably, of the posterior end of the sack and of the overlying corium; and that they accumulate beneath the external membrane of the body, until this is moulted, the rupture beneath being in the meantime healed, when they are freed, or perhaps temporarily protected in the old moulted envelope of the body.

On each side, within the first two segments of the body, and projecting a little before the great ovarian sack (e), two gut-formed organs (f) may be seen, even from the outside, owing to their opacity and dark colour. They lie near the external surface; the first pair of latero-ventral oblique muscles passing between them and the ovarian sack. They are formed of a branching, grape-like mass of opaque, orange-coloured cells. They are intimately united, at their posterior extremities, to the ovarian sack, and I believe open into it; but I cannot say that I demonstrated this. From their absolute identity in structure, and similarity in position, namely, on each side of the lower end of the œsophagus, no doubt is left on my mind that these bodies answer to the true ovaria, which are situated within the body of other cirripedes; and that the ovarian sack answers to the inosculating and branching ovarian tubes and cæca, which fill the peduncle, or cover the basis in other cirripedes, but here, from the absence of these parts, necessarily occupying the body.

Male Organs.--The whole surface of the ovarian sack, the space before it, even to within the lower parts of the mouth, the posterior half of the last thoracic segment, and especially the whole three abdominal segments, are completely netted by branching delicate vessels or ducts terminating in spherical glands about 1/2000th of an inch in diameter. These little glands include a brownish pulpy centre, and sufficiently resemble the testes of other cirripedes in appearance, position, and connecting ducts, to make me believe that such is their nature. I may remark that in the more central parts of the abdomen the glands and ducts seemed to be in process of formation by the confluence of cellular matter, and in some other cirripedes I have suspected that the testes are periodically renewed, or at least redeveloped from an undistinguishable condition. Within the posterior half of the abdomen, some of the ducts become thicker and unite, others joining in laterally, so as together to make a dark chord, 7/2000ths of an inch in diameter. Until dissecting this chord, I thought it was a single vesicula seminalis, but it separated into several rather thick ducts or vesiculæ. I was not able to remove from within them the contained matter, but it appeared very finely and longitudinally flocculent, like spermatozoa not quite matured. In accordance with the immature state of the contents of the ovarian sack, in all probability these ducts would hereafter have become greatly enlarged, and have formed a compound vesicula seminalis of considerable size. The dark chord, formed by their union, contracts as it enters the rudimentary penis, and terminates in a very minute orifice on its apex. The penis consists of a papilla, only 3/4000ths of an inch in length, situated on the extreme point of the abdomen, but rather towards the ventral surface.

Metamorphosis.--In accordance with the general law of the correlation of parts, it may be inferred, from the description and measurements of the pupal antennæ immediately to be given, that this abnormal creature was developed within a pupa of the same general structure, and of about the size, as the pupæ whence Scalpellum, Alcippe, and many other cirripedes are developed. As the ova are of remarkably small size, indeed I have seen no others quite so small, it is certain that the larvæ, as in the case with all other cirripedes, excepting Cryptophialus, must undergo several metamorphoses, and increase much in size, before attaining their pupal condition.

Attachment.--The animal is attached, as already stated, to the sack of the Alepas by two threads, rising close together from the medio-dorsal line, near the posterior end of the second segment of the body. These threads are attached likewise close together at their further ends, by the antennæ, into which they enter. They are flattened and strong, yet quite flexible, with a somewhat sinuous surface: they were, in this specimen, 42/1000ths of an inch in length, and a little above 3/1000ths in diameter: where joined to the thoracic segment they were a little contracted. Their structure in this specimen could be made out (Pl. 24, fig. 1) with perfect distinctness. Their transparent outer tunic (e, fig. 1) is 1/2000ths of an inch in thickness, and is continuous with that (d) enveloping the whole body, but is abruptly and considerably thicker than this membrane; and hence a very slight collar is formed outside, round the line of junction of each thread with the body. The delicate corium (c) lining the external membrane of the body runs, at least someway, down these threads. It was likewise indisputably evident that the membrane (b), for I separated it by dissection, forming the great ovarian sack, together with the cellular contents of this sack (a), entered and extended down both threads. It should, also, be particularly observed, that the coarsely cellular matter within the ovarian sack, immediately that it entered the tube formed by the membrane of the ovarian sack, suddenly changed its appearance into a homogeneous, stiff, pulpy matter, which retained the same appearance all down the threads to within the antennæ. This finer matter readily separated from the coarser cellular matter within the sack, but was not divided from it by any septum or membrane. Some way within the threads, the corium, the membrane of the ovarian sack, and the contents appear (e′), as seen from the outside, to become, and perhaps really are, blended together. These threads could not have been originally formed of their present length, and must therefore have been added to during the growth of the animal; but from their entering the not-moulted antennæ, and from the animal being permanently attached by them, they cannot have grown, by means of the moulting of their integuments; hence I conclude that at each period of growth and exuviation they have been added to only at their upper ends, where there is a sort of collar, or line of growth; and where, I may remark, the lining corium is alone well developed. We shall presently see the bearing of these remarks.

These threads contract to about half their former diameter as they enter the old prehensile antennæ of the pupa, within which they are firmly attached. Each thread, with its three tunics apparently blended together, can be traced to the extremity of the disc-segment (g), where the included matter seems to have burst forth. The whole disc and the terminal segment of both antennæ are enveloped, close together, in cement, formed into two almost separate little capsules, by which they adhere very firmly to the integuments of the Alepas. The cement required to be removed before the antennæ could be plainly seen. The cement presented all the usual characters, namely, its homogeneous laminated structure and its yellowish colour. The cement in the case of the male Ibla, which is parasitic within the sack of the female Ibla, affects the corium and fibrous matter beneath the chitine-tunic, and causes them to adhere together, and thus prevents the male from being cast off each time that the inner tunic of the sack of the female is moulted: exactly so has the cement of the Proteolepas affected the integuments of the Alepas. The only difference between ordinary cement-ducts and the two threads here described is, that the ducts, in both cases formed by the prolongation of the coat of an ovarian receptacle, are here protected by a thick outer membrane, lined, at least in the upper part, by corium; whereas, in the Lepadidæ the two ducts are included within the peduncle, and are therefore protected by one common membrane, lined of course by corium; and this membrane, we shall presently see, is homologous with that separately investing the two threads.

The antennæ differ remarkably little, considering the anomalous character of the mature animal, from the same organ in other genera; they come nearest, perhaps, to the antennæ of Ibla. The length of the disc (g, fig. 1) and great succeeding segment (f) together is 40/6000ths of an inch. The lower segment has its basal articulation only slightly oblique, showing that, as in Alcippe and Ibla, it was probably articulated near the anterior end of the pupal shell: it is of nearly the same width throughout.[154] The disc (g) is remarkable from its great proportional length; it is hoof-shaped, with the outer side rather protuberant, and the end pointed. The ultimate segment (h) is of moderate size: as in Ibla, it has a shoulder or notch on its inner side near its end, bearing two long spines; and probably there were originally three or four spines on the square broad upper end, but these have been broken. This segment is articulated unusually near to the end of the disc.

[154] As I have given the measurements of the antennæ in so many genera, I will give these: second (f, fig. 1) segment, 24/6000ths of an inch in length, and (8-9)/6000ths in width. Disc, 16/6000ths in length, and 8/6000ths in width. Ultimate segment, 6/6000ths (?) in length, and 10/20,000ths (?) in breadth.

The foregoing remarks on the two threads by which Proteolepas is attached, are, independently of their relation to this individual animal, of considerable interest. In my volume on the Lepadidæ, I have stated, after repeated and rigorous examinations (for I was well aware how singular the facts were), that in Conchoderma aurita and in some other genera, the cement-ducts, which entered the pupal antennæ, could be traced till they joined a gland, the coat of which gland was absolutely continuous with the coats of the adjoining and continuous ovarian tubes, of which it was only a modified portion; and what was still more remarkable, that the matter within the gland was continuous with, and differed only from, the cellular matter within the ovarian tubes and cæca (from which ova were in the act of formation), by being more homogeneous and more coherent. Furthermore, I have shown, that in Ibla an ovarian tube, becomes by a very small change, namely, by a double flexure and slight thickening of its coat, converted into a gland, and thus acquires the power of affecting the cellular ovarian matter and changing it into cement. Now, in Proteolepas, the great ovarian sack replaces the ovarian tubes and cæca; and we here see the very same relations even still more plainly; for the coat of the ovarian sack is indisputably continuous with that investing or forming the two cement-ducts within the two threads; and immediately that the coarse cellular matter, which within the ovarian sack is being converted into ova, enters the upper contracted end of the cement-duct, by some power, we must suppose, inherent in its coat, it is converted into cement, which debouches with all its usual properties through the pupal antennæ. I may venture to reaffirm that nothing could be plainer than this structure, or be in more striking conformity with my previous observations, given in the introduction to the Lepadidæ.

* * * * *

I can hardly express the perplexity which I felt when I first examined Proteolepas, and when I naturally mistook the mouth for the entire head, for I saw, as I thought, the antennæ in direct connection with the second segment of the body, posteriorly to the mouth! It was quite as monstrous and incredible an inversion of the laws of nature, as those fabulous half-human monsters, with an eye seated in the middle of their stomachs. After a time, I perceived that the following considerations removed all difficulty, and brought Proteolepas into the type of other cirripedes.

Firstly: in ordinary cirripedes, the two cement-ducts can be traced up from the cemented antennæ to the glands, formed by a part of the ovarian branching cæca; and the latter can be traced to where they enter, as two simple tubes, the body of the animal, at a medio-dorsal point, a little anteriorly to the prosoma, or second thoracic segment.[155] From what is actually seen in the complemental male of Scalpellum Peronii, and from what may be inferred from the structure of these parts in the pupæ of all cirripedes, there can be no doubt that if the ovarian cæca were in any case not developed, the cement-ducts would enter the body at the spot where the two simple ovarian tubes, which serve to unite the ovarian cæca with the true ovaria, do enter. Now if we look at the drawing (Pl. 25, fig. 7) of Proteolepas, we shall see that the cement-ducts enter the body at a medio-dorsal point, a little anteriorly to the second thoracic segment, and therefore in the normal position.

[155] This may be partially seen in the section, fig. 1, of Balanus, on the same plate (25) with the figure of Proteolepas; here (bearing in mind that Balanus is a much modified form) (z) shows the pupal antennæ, within which, whilst young, the cement-ducts are included, and are directly continuous with the layer of branching ovarian cæca (g), which are prolonged up to the ovaria as a pair of simple tubes (only one being here represented), entering the body above the upper margin of the prosoma (c). The prosoma of Balanus, I may add, answers to the segment ^2 t in fig. 7 of Proteolepas; (e) the mouth in Balanus, of course corresponding with (m) the mouth of Proteolepas; the segment ^1 c and ^2 t of the latter, are in Balanus aborted or confluent, at least on the ventral surface; and, lastly, the whole great shell of Balanus, the sack with its muscles and the branchiæ, and the opercular valves with their muscles, are all represented in Proteolepas merely by the outer membrane of the two threads (g), which enter the pupal antennæ!

Secondly: the external membrane of the two threads, investing the two cement-ducts, it should be remembered, is not moulted, and is added to during growth (being lined internally by corium), only round the upper, collar-like edge.

Thirdly: the external covering or carapace of every young cirripede, at the period of its metamorphosis, enters, at its lower end, the cemented antennæ, in the form of two short tubular prolongations, by which alone, at first, the cirripede adheres to the surface of attachment; within these prolongations the cement-ducts are included. I have, moreover, seen instances, as in Conchoderma aurita and in the male of Ibla and Alcippe, in which these tubular prolongations, lined internally by corium, were increased a little in length, so as to form a trouser-like termination to the peduncle. That the forked extremity should be a little more developed, and so be converted into a pair of short tubular threads, cannot be considered as very improbable.

Fourthly: in the male Ibla the capitulum is so much atrophied that it does not enclose the thorax or mouth, but still an elongated support or peduncle is left. But it would be no very violent assumption to imagine the peduncle, which does not essentially differ from the capitulum, to become likewise rudimental,--to grow smaller and smaller, and shorter and shorter, till the merest remnant was left at the spot where it entered the cemented antennæ. And in the last paragraph it has been shown that it would be no violent assumption to imagine this lower end of the peduncle, where it enters the antennæ, developed into two short thread-like prolongations.

Lastly: it is certain, from the existence of the prehensile antennæ, that Proteolepas was developed within a pupa, probably differing in no very essential respect from the pupæ of other cirripedes. Therefore, in accordance with all analogy, we may believe that the position[156] of the young Proteolepas (probably much coiled up, with a deep fold close under the mouth) within the pupa, the general form and structure of the latter, and the course of the cement-ducts, did not essentially differ from the imaginary figure given, Pl. 25, fig. 6. Now, at the period of the metamorphosis, let us imagine that no general covering or carapace was formed, except a small portion on the ventral surface, round the cemented antennæ. Let us further suppose this remnant to be specially developed (as in the case of some cirripedes) into a short trouser-like prolongation, entering the antennæ; and subsequently, in accordance with the almost universal laws of growth in cirripedes, that this portion was never moulted, but continued to be added to, during growth, only at its upper end. By this means we should produce every leading peculiarity of the Proteolepas bivincta. As this parasite lives within the sack of another cirripede, and is protected by the capitulum of the latter, we can understand, in accordance with the usual admirable economy of nature, the absence of any general covering for its body. We can now, also, understand the structure and manner of growth of the two threads by which it is bound to its prey; and the connection, at first so strange and perplexing, between the old pupal antennæ and the second segment of the thorax. I am convinced that no other explanation than that here given, will accord with the relations of the several parts and organs of Proteolepas. Consequently, I fully believe that we here see an articulate animal in which the whole of the three anterior segments of the head have been, during the act of metamorphosis, absolutely aborted, with the exception of a mere rudiment on the ventral surface, near the anterior end, round the old antennæ, and which rudiment has been specially developed as a covering for the two cement-ducts. As the pupal antennæ are, homologically, the second pair of antennæ, we may further infer that this modified remnant of the carapace, investing the two threads, belongs to the third cephalic segment.

[156] Any one who has not specially attended to the metamorphoses of ordinary cirripedes, who looks at the imaginary figure of the young Proteolepas, will feel much surprise at the relative positions of the parts; for the mouth and the first and even second segments of the body stand posteriorly (i. e. above in the figure) to the succeeding segments of the body, in relation to the carapace of the pupa; but this is only in accordance with the remarkable change in position (as explained in the introduction, p. 123, pl. 30, fig. 2), amounting almost to inversion, which the whole thorax of every young cirripede undergoes within the pupa, whilst the anterior cephalic portions and general covering are developed conformably with the pupal carapace, whence it arises that the dorsal surface of that part of the thorax immediately succeeding the mouth becomes attached to the ventral internal surface of the carapace. I believe that the peculiar flattened dorsal outline of the first two segments of the body of Proteolepas is due to these parts having been formed in contact (as represented in pl. 25, fig. 6) with the straight ventral surface of the carapace of the pupa. To place the young Proteolepas, and at the same time the carapace of the pupa, with all the parts in proper homological sequence, it would be necessary to seize the posterior end of the abdomen (a), and pull till the dorsal surfaces of the first and second segments of the body, separated from the ventral internal surface of the carapace, and stood posteriorly (i. e. above in figure) to the mouth, which latter would thus also have to rotate a quarter of a circle, so that the orifice would come to be directed outwards. Then every part would stand, in accordance with the archetype crustacean structure, in due order; but the three confluent anterior cephalic segments, forming the front part and carapace of the pupa, would, as in the case of all cirripedes, be of disproportionately large size in relation to the rest of the body.

SYNOPSIS

ET

INDEX SYSTEMATICUS.

Ordinum, Familiarum, et Generum Cirripediorum et recentium et fossilium.

CLASSIS CRUSTACEA.

Sub-classis CIRRIPEDIA.

Crustacea ex anteriore capitis parte defixa, cæmento in hunc usum ex ovariorum portione ad id specialiter modificatâ emisso. Archetypus è segmentis 17 compositus, quorum 3 priora magna, in carapacem sæpissimè conformata, quæ non omnino exuitur et varios motus efficit: antennæ nullæ: oculi rudimentarii: os prominens, formatum è labro, palpis, mandibulis, et duobus maxillarum paribus, quæ omnia partim confluunt: thorax ad superficiem internam sternalem carapacis affixus, plerumque cum membrorum captantium biramorum, multiarticulorum paribus 6: abdomen plerumque rudimentarium: branchiæ, si quæ adsunt, ad inferiora carapacis latera affixæ: plerumque bisexualia; in unisexualibus, mares fœminis parasitice inserti: penis unicus, plerumque probosciformis, ad posteriorem abdominis extremitatem situs: oviductus nulli: metamorphoses multiplices.

ORDO I. THORACICA. (Darwin, 'Balanidæ,' p. 30.)

Cirripedia quibus pro carapace est aut capitulum pedunculatum, aut testa operculata cum basi. Corpus è 6 thoracicis segmentis, ferè cum 6 cirrorum paribus, constat. Abdomen rudimentarium, sed sæpe cum appendiculis caudalibus. Oris labrum motus proprios non efficit. Larva primò monocula cum 3 crurum paribus, postremò binocula cum 6 crurum thoracicorum paribus.

Familia 1. BALANIDÆ. (Darwin, 'Balanidæ,' p. 33.)

Cirripedia sine pedunculo: scuta et terga musculis depressoribus instructa: reliquæ testæ valvæ inter se immobiliter conjunctæ.

Sub-Familia 1. BALANINÆ. (Darwin, 'Balanidæ,' p. 175.)

Rostrum cum radiis, sed sine alis; valvæ testæ laterales omnes, ex uno latere alis, ex altero radiis instructæ: parietes ferè aut porosi aut ad interiorem superficiem longitudinaliter costati.

[Sectio †.]

Scutum et tergum inter se articulata aut mutuò interclusa: branchiarum unaquæque ex unicâ plicâ constat.

1. Genus--BALANUS, Auctorum. (Darwin, 'Balanidæ,' p. 177.)

Valvæ testæ 6; basis calcarea aut membranacea; valvæ operculares subtriangulares.

2. Sub-Genus--ACASTA, Leach. (Darwin, 'Balanidæ,' p. 302.)

Valvæ testæ 6; parietes et basis non porosa; basis calcarea, cyathiformis, non elongata. Spongiis, aut rarò Isidis cortici, affixa.

3. Genus--TETRACLITA, Schumacher. (Darwin, 'Balanidæ,' p. 321.)

Valvæ testæ 4; interdum inter se externè confluentes: parietes poris perforati, multis plerumque seriebus; basis plana, irregularis, calcarea aut membranacea.

4. Genus--ELMINIUS, Leach. (Darwin, 'Balanidæ,' p. 345.)

Valvæ testæ 4; parietes non porosi; basis membranacea.

5. Genus--PYRGOMA, Leach. (Darwin, 'Balanidæ,' p. 354.)

Valvæ testæ in unam confluentes; basis cyathiformis aut subcylindrica, coraliis affixa.

6. Sub-Genus--CREUSIA, Leach. (Darwin, 'Balanidæ,' p. 375.)

Valvæ testæ 4, radiis instructæ; basis cyathiformis, coraliis affixa.

7. Genus--CHELONOBIA, Leach. (Darwin, 'Balanidæ,' p. 382.)

Valvæ testæ admodum crassæ, 6; sed ex iis, valva rostralis intùs è tribus valvis rudimentariis conjunctis constat; basis membranacea; scuta angusta, tergis cristâ articulari corneâ conjuncta.

[Sectio ††.]

Scutum et tergum (ubi ambo adsunt) non inter se articulata; basis membranacea; parietes sæpe profundè plicati, laminâ exteriore, ad basin versâ, plerumque imperfectâ; branchiarum unaquæque e duobus plicis constat. Testa vertebratis vivis affixa.

8. Genus--CORONULA, Lamarck. (Darwin, 'Balanidæ,' p. 397.)

Valvæ testæ 6; æquali latitudine; parietes tenues, profundè plicati, plicis cavitates infrà solùm apertas efficientibus; valvæ operculares orificio testæ multo minores. Cetaceis affixa.

9. Genus--PLATYLEPAS, J. E. Gray. (Darwin, 'Balanidæ,' p. 424.)

Valvæ testæ 6; unaquæque bilobata et intùs producta, ita ut 6 medias costas longitudinales efficiant, quæ basin membranaceam extrorsùs convexam sustinent.

10. Genus--TUBICINELLA, Lamarck. (Darwin, 'Balanidæ,' p. 430.)

Valvæ testæ 6, æquali latitudine; testa subcylindrica, orificio latiore quam basis, pluribus cristis transversis virgata. Cetaceis affixa.

11. Genus--XENOBALANUS, Steenstrup. (Darwin, 'Balanidæ,' p. 438.)

Testa pæne rudimentaria, stelliformis, è valvis 6 formata, è quarum medio corpus longum pedunculiforme exoritur; valvæ operculares absunt. Cetaceis affixus.

Sub-Familia 2. CHTHAMALINÆ. (Darwin, 'Balanidæ,' p. 446.)

Rostrum cum alis sed sine radiis; valvæ rostro-laterales utrinque sine alis; parietes non porosi.

12. Genus--CHTHAMALUS, Ranzani. (Darwin, 'Balanidæ,' p. 447.)

Valvæ testæ 6; basis membranacea, sed interdum ad speciem calcarea, ideò quod parietes inflectuntur.

13. Genus--CHAMÆSIPHO, Darwin. ('Balanidæ' p. 470.)

Valvæ testæ 4, suturis sæpe admodùm obliteratis; basis membranacea.

14. Genus--PACHYLASMA, Darwin. ('Balanidæ,' p. 475.)

Valvæ testæ, conchâ recenter natâ, 8; adultâ aut 6, aut ad speciem 4, ideò quod valvæ laterales arctè conjunguntur; basis calcarea.

15. Genus--OCTOMERIS, G. B. Sowerby. (Darwin, 'Balanidæ,' p. 482.)

Valvæ testæ 8; radii marginibus crenatis; basis membranacea.

16. Genus--CATOPHRAGMUS, G. B. Sowerby. (Darwin, 'Balanidæ,' p. 485.)

Valvæ testæ interiores 8, cum pluribus exterioribus parvarum supplementalium valvarum verticillis; basis aut membranacea aut calcarea.

Familia 2. VERRUCIDÆ. (Darwin, 'Balanidæ,' p. 495.)

Cirripedia sine pedunculo; scuta et terga, musculis depressoribus non instructa, ex uno latere tantum mobilia, ex altero cum carinâ et rostro in testam asymmetricam immobiliter conjuncta.

1. Genus--VERRUCA, Schumacher. (Darwin, 'Balanidæ,' p. 496.)

Familia 3. LEPADIDÆ. (Darwin, 'Lepadidæ,' p. 8, et 'Balanidæ,' p. 526.)

Cirripedia pedunculo flexili, musculis instructo; scuta et terga (si qua adsunt) musculis depressoribus non instructa; reliquæ valvæ (si quæ adsunt) in annulum immobilem non conjunctæ.

1. Genus--LEPAS, Linn. (Darwin, 'Lepadidæ,' p. 67.)

Valvæ 5, approximatæ; carina sursùm inter terga extensa, deorsùm aut furcâ infossâ aut disco externo terminata; scuta subtriangula, umbonibus ad angulum rostralem positis.

2. Genus--PŒCILASMA, Darwin. ('Lepadidæ,' p. 99.)

Valvæ 3, 5, aut 7, approximatæ; carina solùm ad basales apices tergorum extensa, termino basali aut truncato aut in discum profunde infossum producto; scuta pænè ovalia, umbonibus ad angulum rostralem positis.

3. Genus--DICHELASPIS, Darwin. ('Lepadidæ,' p. 115.)

Valvæ 5, quæ ferè pro septem haberi possent, scuto in segmenta planè duo, ad angulum autem rostralem conjuncta, diviso; carina plerumque sursum inter terga extensa, deorsum aut disco infosso aut furcâ aut calyce terminata.

4. Genus--OXYNASPIS, Darwin. ('Lepadidæ,' p. 133.)

Valvæ 5, approximatæ; scutorum umbones in medio marginis occludentis positi; carina rectangulè flexa, sursùm inter terga extensa, termino basali simpliciter concavo.

5. Genus--CONCHODERMA, Olfers. (Darwin, 'Lepadidæ,' p. 136.)

Valvæ 2 ad 5, minutæ, inter se remotæ; scuta bi- aut tri-lobata, umbonibus in medio marginis occludentis positis; carina arcuata, terminis utrinque pæne similibus.

6. Genus--ALEPAS, S. Rang. (Darwin, 'Lepadidæ,' p. 156.)

Capitulum aut sine valvis, aut scutis corneis, pæne abditis.

7. Genus--ANELASMA, Darwin. ('Lepadidæ,' p. 169.)

Capitulum sine valvis; aperturâ amplâ; pedunculus fimbriatus, sub-globosus, infossus.

8. Genus--ALCIPPE, Hancock. (Darwin, 'Balanidæ,' p. 529.)

(Fœm.) Capitulum sine valvis, aperturâ spinosâ; pedunculus ad basalem extremitatem crescit; superficie rostrali depressâ et disco corneo tectâ; capitulum et pedunculus in cavitate conduntur, ab ipso cirripedio formatâ.

9. Genus--IBLA, Leach. (Darwin, 'Lepadidæ,' p. 180.)

(Herm. et Fœm.) Valvæ 4, corneæ; pedunculus spinis corneis, persistentibus vestitus.

10. Genus--SCALPELLUM, Leach. (Darwin, 'Lepadidæ,' p. 215, et 'Lepad. Foss.' p. 13.)

(Herm. et Fœm.) Valvis 12 ad 15; lateribus verticilli inferioris quatuor vel sex, lineis incrementi plerumque convergentibus; sub-rostrum rarissime adest; pedunculo squamifero, rarissime nudo.

CHARACTERES VALVARUM IN SPECIEBUS FOSSILIBUS.

Carina angusta, introrsùm arcuata, ab apice ad marginem basalem paululum dilatata; carinæ parietes valde inflexi, costis manifestis a tecto plerumque disjuncti; in multis speciebus intra-parietibus instructa; intraparietes nonnunquam supernè producti ultra umbonem carinæ, qui fit inde subcentralis; carinæ parietum lineæ incrementi perobliquæ. Scuta plerumque subconvexa et tenuia, trapezoidea; marginibus tergalibus lateralibusque angulo insigni disjunctis.

11. Genus--POLLICIPES, Leach. (Darwin, 'Lepadidæ,' p. 293, et 'Lepad. Foss.' p. 42.)

Valvæ ab 18 usque ad 100 et amplius; lateribus verticilli inferioris multis; lineis incrementi deorsùm ordinatis; subrostrum semper adest; pedunculus squamiferus.

CHARACTERES VALVARUM IN SPECIEBUS FOSSILIBUS.

Carina ab apice ad marginem basalem multum dilatata, apice plerumque liberè prominente; carinæ parietes à tecto non distincté separati, lineis incrementi parietum parum obliquis. Scuta plerumque subsolida, convexa, subtrigonalia, margine tergo-laterali plus minusve eminente, sed non angulo in margines duos discreto.

12. Genus--LITHOTRYA, G. B. Sowerby. (Darwin, 'Lepadidæ,' p. 332.)

Valvæ 8, si inter eas parvum (sæpe rudimentale) rostrum et duo parva latera numerentur; incrementi lineis concinnè crenatis; pedunculus squamis calcareis parvis vestitus, in verticillis superioribus crenatis, aut calyci basali calcareo aut discorum ordini affixus.

13. Genus--LORICULA, G. B. Sowerby, jun. (Darwin, 'Lepad. Foss.' p. 81.)

Capitulo decem (fortasse) valvis instructo. Pedunculo seriebus decem squamarum lævium calcarearum instructo; sex lateralibus multum transversè elongatis; quatuor terminalibus angustis; secundùm pedunculi margines rostralem et carinalem decurrit sutura medialis recta, squamis non intersecantibus.

ORDO II. ABDOMINALIA. (Darwin, 'Balan.' p. 563.)

Cirripedia quibus carapax lageni-formis est; corpus ex 1 cephalico, 7 thoracicis, 3 abdominalibus segmentis constat; quorum abdominalia tribus cirrorum paribus muniuntur; thoracica membris carent. Oris labrum longè producitur et motus proprios efficit; œsophagi inferior extremitas dentibus munitur. Larva, primò ovöides, sine externis membris, sine oculo; postremò binocula, thoracicis cruribus nullis.

1. Genus--CRYPTOPHIALUS, Darwin. ('Balanidæ,' p. 566.)

ORDO III. APODA. (Darwin, 'Balan.' p. 587.)

Cirripedia quibus carapax ad duo separata fila (quæ defigendo inserviunt) redactus est. Corpus ex 1 cephalico, 7 thoracicis, 3 abdominalibus segmentis constat, quæ omnia cirris carent. Os suctorium, mandibuli et maxillæ (dorsis inter se appositis) cucullo includuntur, qui è labro et palpis confluentibus formatur. Metamorphoses incognitæ.

1. Genus--PROTEOLEPAS, Darwin. ('Balanidæ,' p. 589.)

SYNOPSIS

ET

INDEX SYSTEMATICUS SPECIERUM,

Et recentium, et fossilium.[157]

[157] In hâc portione Synopsis, Auctorum nomina referunt solummodo ad species.

ORDO I. THORACICA.

Fam. BALANIDÆ.

Sub-Fam. BALANINÆ.

[Sectio †.]

1. Genus--BALANUS.

Sectio A.

Parietes et basis et radii poris perforati.

Sectio B.

Parietes et basis interdum poris perforati; radii nunquam; testæ axis rostro-carinalis elongatus; basis cymbiformis, Gorgoniis et Milleporis affixa.

Sectio C.

Parietes et basis semper poris perforati; radii nunquam.

Sectio D.

Parietes semper poris perforati; basis et radii nunquam.

Sectio E.

Basis membranacea.

Sectio F.

Parietes et radii nunquam, basis interdum, poris perforata; basis interdum admodum tenuis, adeo ut vix distingui possit.

[Sectio A.]

1. Balanus tintinnabulum, Linn. (Darwin, 'Balanidæ,' p. 194, Tab. 1 et 2, fig. 1.)

B. testâ à roseâ ad atropurpuream variante, sæpe longitudinaliter virgatâ et costatâ. Orificio plerumque integro, interdum dentato. Scuti cristâ articulari latâ et reflexâ. Tergi margine basali plerumque in contrariis calcaris partibus rectam lineam formante.

Hab.--In tepidis et torridis ubique maribus. Foss. in Europâ.

2. Balanus tulipiformis, Ellis. (Darwin, 'Balanidæ,' p. 204, Tab. 2, fig. 2.)

B. testâ, obscurè roseâ, interdum purpurascente; orificio dentato. Scuto externè admodum lævi membranâ tecto. Tergi musculorum depressorum cristis distinctis.

Hab.--In Europâ meridionali et Madeirâ.

3. Balanus psittacus, Molina. (Darwin, 'Balanidæ,' p. 206, Tab. 2, fig. 3.)

B. testâ pallidè roseâ, sordidâ; orificio hexagonali. Scuti cristâ articulari minimâ, quæ cum adductoris cristâ, admodum prominente, confluit; musculo depressore laterali tubulari cavitate locato, quæ sursùm ad valvæ apicem extendit. Tergi apice producto, aculeato, purpureo; calcare ab angulo basi-scutali propiùs quam suâ ipsius latitudine distante.

Hab. et foss. in Americâ meridionali.

4. Balanus Capensis, Ellis. (Darwin, 'Balanidæ,' p. 209, Tab. 2, fig. 4.)

B. testâ colore lucidè-roseo, umbratâ et sæpe longitudinaliter virgatâ. Scuto ut in B. psittaco. Tergi apice producto aculeato, albo; calcare ab angulo basi-scutali suâ ipsius latitudine distante.

Hab.--In Africâ meridionali.

5. Balanus nigrescens, Lamarck. (Darwin, 'Balanidæ,' p. 210, Tab. 2, fig. 5.)

B. testâ cinereâ, pallidè-cæruleo aut atro-cæruleo, aut albo tinctâ. Scuti cristâ articulari parvâ, deorsùm in parvum, acutum aculeum desinente; adductoris cristâ prominente. Tergi apice producto, aculeato.

Hab.--In Australiâ.

6. Balanus decorus, Darwin. ('Balanidæ,' p. 212, Tab. 2, fig. 6.)

B. parietibus pallidè-roseis: radiis aliquanto intensioribus. Scuti cristâ articulari parvâ. Tergi sulco longitudinali admodum tenui et aperto; marginibus basalibus utrinque ad calcar declivibus.

Hab.--In Novâ Zealandiâ.

7. Balanus vinaceus, Darwin. ('Balanidæ,' p. 213, Tab. 2, fig. 7.)

B. testâ fusco-purpureâ; parietum laminâ interiore cancellatâ. Scuto longitudinaliter et tenuiter striato. Tergi sulco longitudinali tenui et aperto: marginibus basalibus utrinque ad calcar declivibus.

Hab.--In occidentali littore Americæ merid.

8. Balanus Ajax, Darwin. ('Balanidæ,' p. 214, Tab. 3, fig. 1.)

B. testâ globoso-conicâ, sæpe in axe rostro-carinali elongatâ, pallidè-roseâ, lævi, admodum crassâ: tubis parietalibus prope marginem basalem, cylindricis et minimis. Scuti cristâ articulari latâ, reflexâ.

Hab.--In Arch. Philippino.

[Sectio B.]

9. Balanus stultus, Darwin. ('Balanidæ,' p. 216, Tab. 3, fig. 2.)

B. parietibus et basi porosis: testâ albâ aut purpurâ leviter tinctâ. Scuti margine basali in medio prominente. Tergi sulco longitudinali supernè clauso; calcare angulo basi-scutali non approximato.

Hab.--In Indiâ occident. et orient.

10. Balanus calceolus, Pallas. (Darwin, 'Balanidæ,' p. 218, Tab. 3, fig. 3.)

B. parietibus et basi porosis. Scuto musculi depressoris lateralis fossâ parvâ, profundâ.

Hab.--In Africâ occidentali et Indiâ. Foss. in Angliâ.

11. Balanus galeatus, Linn. (Darwin, 'Balanidæ,' p. 220, Tab. 3, fig. 4.)

B. parietibus non porosis: basi porosa. Tergi apice, propter cristæ articularis magnitudinem, quadrato.

Hab.--In Americâ sept. et Indiâ occident.

12. Balanus cymbiformis, Darwin. ('Balanidæ,' p. 221, Tab. 3, fig. 5.)

B. parietibus et basi non porosis. Scuti et tergi cristis articularibus minimis. Tergo lato, pæne æquilaterali.

Hab.--In Indiâ.

13. Balanus navicula, Darwin. ('Balanidæ,' p. 221, Tab. 3, fig. 6.)

B. parietibus et basi non porosis: valvis testæ carino-lateralibus admodùm angustis, latitudine à vertice ad imum pæne æquâ. Radiorum marginibus suturalibus lævibus. Scuto externè longitudinaliter striato.

Hab.--In Indiâ.

[Sectio C.]

14. Balanus trigonus, Darwin. ('Balanidæ,' p. 223, Tab. 3, fig. 7.)

B. parietibus costatis, purpureo-rubris, maculatis: orificio lato, trigonali, vix dentato. Scuto crasso, fossularum seriebus longitudinalibus 1 ad 6. Tergo sine sulco longitudinali; calcare truncato ad plenùm 1/3 valvæ latitudine.

Hab.--In Arch. Indiæ Orient.: Australiâ: Californiâ: Peruviâ.

15. Balanus spongicola, Brown. (Darwin, 'Balanidæ,' p. 225, Tab. 4, fig. 1.)

B. parietibus plerumque lævibus, interdum longitudinaliter plicatis; roseis; orificio dentato: scuto longitudinaliter striato: tergum, apice producto, sine sulco longitudinali; calcare truncato 1/3 valvæ latitudine.

Hab.--In Europâ meridionali et mediâ, Africâ meridionali; var. in Indiâ occidentali. Foss. in Angliâ, in "Miocenâ Formatione."

16. Balanus lævis, Bruguière. (Darwin, 'Balanidæ,' p. 227, fig. 2.)

B. testâ aut fuscâ membranâ testâ, aut nudâ et albâ, aut pallide-purpureâ: orificio parvo: radiis minimis: scuto 1 aut 2 sulcis longitudinalibus profundis.

Hab.--In littore occidentali Americæ utriusque.

17. Balanus perforatus, Bruguière. (Darwin, 'Balanidæ,' p. 231, Tab. 4, fig. 3, et Tab. 5, fig. 1.)

B. testâ sordidâ, pallidè-purpureâ aut albâ aut cinereâ, lævi aut propter corrosionem longitudinaliter tenuiter costatâ; vaginâ purpureâ; orificio plerumque parvo: radiis plerumque angustis aut nullis: scuto introrsus cristâ brevi minutâ sub cristam adductoris prominentem proximè et parallelè positâ: tergi apice aliquantum producto.

Hab.--In Europâ meridionali et mediâ; in Africâ occidentali.

18. Balanus concavus, Bronn. (Darwin, 'Balanidæ' p. 235, Tab. 4, fig. 4.)

B. testâ, albo cum roseo aut obscurè purpureo longitudinaliter striatâ; interdum pure albâ: scuto longitudinaliter tenuiter striato; internè adductoris cristâ admodum aut modicè prominente.

Hab.--In Peruviâ, Californiâ, Arch. Philippino, Australiâ. Et foss. in Europâ, Americâ septent. et meridionali.

19. Balanus amphitrite, Darwin. ('Balanidæ,' p. 240, Tab. 5, fig. 2.)

B. testâ purpureo aut roseo longitudinaliter striatâ; striis interdum confluentibus; interdum pure albâ: scutum internè adductoris cristâ prominente.

Hab.--In tepidis et torridis ubique maribus.

20. Balanus pœcilus, Darwin. ('Balanidæ,' p. 246, Tab. 5, fig. 3.)

B. testâ obscurè rubrâ albo maculatâ scuto internè adductoris cristâ nullâ tergi calcare præcisè truncato, ferè 1/3 valvæ latitudine.

Hab.--In littore occident. Americæ merid.

21. Balanus eburneus, A. Gould. (Darwin, 'Balanidæ,' p. 248, Tab. 5, fig. 4.)

B. testâ flavescente albâ: scuto longitudinaliter tenuiter striato: tergi calcare truncato, margine basi-carinali ferè admodùm excavato; margine carinali supernè prominente.

Hab.--In Americâ septent. et Indiâ occident.

22. Balanus improvisus, Darwin. ('Balanidæ,' p. 250, Tab. 6, fig. 1.)

B. testâ albâ: radiis angustis, marginibus superioribus lævibus, leniter arcuatis, admodùm obliquis: tergi sulco longitudinali; calcaris, termino rotundato.

Hab.--In Europâ, et Americæ utriusque littoribus orient. et occident.

23. Balanus nubilus, Darwin. ('Balanidæ,' p. 253, Tab. 6, fig. 2.)

B. testâ albâ, irregulari: basi alicubi imperfecte porosâ: scuti cristâ articulari minutâ; adductoris cristâ prominente, fossam profundam musculo depressori præbente: tergo introrsus purpureâ maculâ majore notato; apice producto, purpureo.

Hab.--In Californiâ.

24. Balanus corrugatus, Darwin. ('Balanidæ,' p. 254, Tab. 6, fig. 3.)

B. testâ albâ longitudinaliter plicatâ: radiis angustis: scuto internè sine adductoris cristâ.

Foss. in Italiâ.

[Sectio D.]

25. Balanus porcatus, Da Costa. (Darwin, 'Balanidæ,' p. 256, Tab. 6, fig. 4.)

B. testâ albâ, plerumque longitudinaliter acutè costatâ: radiorum marginibus superioribus pæne basi parallelis: scuto longitudinaliter striato; tergi apice producto, purpureo.

Hab. et foss. in Europâ, et Americâ septent. et regionibus Arcticis.

26. Balanus patellaris, Spengler. (Darwin, 'Balanidæ,' p. 259, Tab. 6, fig. 5.)

B. testâ depressâ fuscâ, plerumque obscuro-violaceo longitudinaliter striatâ: radiorum marginibus superioribus (in adultis speciminibus) rotundatis, superficie sulcis tenuibus basi parallelis: basi interdùm poris imperfectis perforatâ: scuto internè cum adductoris cristâ.

Hab.--In Indiâ et Arch. Philippino.

27. Balanus crenatus, Bruguière. (Darwin, 'Balanidæ,' p. 261, Tab. 6, fig. 6.)

B. testâ albâ: radiorum marginibus superioribus obliquis, asperis, rectis: scuto sine adductoris cristâ: tergi calcare rotundato.

Hab. et foss. in Europâ, et Americâ septent. et regionibus Arcticis, et Indiâ occident. et Africâ meridionali.

28. Balanus glandula, Darwin. ('Balanidæ,' p. 265, Tab. 7, fig. 1.)

B. testâ albâ; parietum laminâ internâ longitudinaliter et fortiter costatâ, poris imperfectis et minutis, interdùm alicubi nullis: radiis angustis marginibus superioribus rotundatis: scuto cum adductoris cristâ: tergi calcare truncato, rotundato.

Hab.--In Californiâ, et Oceano Pacifico meridion.

[Sectio E.]

29. Balanus balanoides, Linn. (Darwin, 'Balanidæ,' p. 267, Tab. 7, fig. 2.)

B. parietibus aut solidis, aut cancellatis, aut (rarò) unicâ pororum serie formatis: tergi calcare obtuso aut acuto.

Hab.--In Europâ et Americâ septent. et regionibus Arcticis.

30. Balanus cariosus, Pallas. (Darwin, 'Balanidæ,' p. 273, Tab. 7, fig. 3.)

B. parietibus crassis, pluribus seriebus pororum inæqualium formatis; tergo angusto, apice rostrato, calcare acuminato.

Hab.--In littore occident. Americæ septent. et Freto Behringi et Insulis Kuriliis.

31. Balanus declivis, Darwin. ('Balanidæ,' p. 275, Tab. 7, fig. 4.)

B. parietibus solidis: rostro, carinâ et valvis carino-lateralibus pæne duplo longiore, basi igitur obliquâ: tergi calcare truncato, 1/2 valvæ latitudine.

Hab.--In Indiâ occident.

[Sectio F.]

32. Balanus Hameri, Ascanius. (Darwin, 'Balanidæ,' p. 277, Tab. 7, fig. 5.)

B. testâ albâ: radiorum marginibus superioribus obliquis, lævibus, arcuatis; aciebus suturalibus lævibus: basi solidâ: scuto longitudinaliter, debiliter striato: tergi calcare angusto.

Hab. et foss. in Europâ septent. et Americâ septent.

33. Balanus amaryllis, Darwin. ('Balanidæ,' p. 279, Tab. 7, fig. 6.)

B. testâ subroseo-purpureo striatâ, aut obnubilatâ; interdùm purè albâ: radiis angustis, marginibus superioribus obliquis lævibus, arcuatis: basi porosâ: scuto longitudinaliter planè striato: tergi calcare angusto.

Hab.--In Indiâ, et Arch. Indiæ orient. et Australiâ septent.

34. Balanus allium, Darwin. ('Balanidæ,' p. 281, Tab. 7, fig. 7.)

B. testâ pallidè purpuratâ, radiis latis, marginibus superioribus non obliquis: basi porosâ: scuto lineis incrementi crenatis: tergi calcare admodum brevi, truncato, 1/2 valvæ latitudine.

Hab.--In Australiâ septent.

35. Balanus cepa, Darwin. ('Balanidæ,' p. 283, Tab. 7, fig. 8.)

B. testâ sordidè rubro-purpureâ, abruptè conicâ: radiis angustis: basi obscurè porosâ: scuto lineis incrementi crenatis: tergi calcare truncato, dimidiâ valvæ latitudine, et infrà angulum basi-scutalem dependente, usque ad 1/2 sui ipsius latitudinem.

Hab.--In Japaniâ.

36. Balanus quadrivittatus, Darwin. ('Balanidæ,' p. 284, Tab. 8, fig. 1.)

B. testâ abruptè conicâ, quatuor vittis longitudinalibus transversè positis: radiorum marginibus superioribus obliquis: basi tenui, solidâ: scuto, lineis incrementi lævibus; musculi depressoris lateralis fossâ distinctâ nullâ: terga ut in B. cepâ.

Hab.--In Archipel. Indiæ orient.

37. Balanus terebratus, Darwin. ('Balanidæ,' p. 285, Tab. 8, fig. 2.)

B. testâ albâ, costis longitudinalibus fortibus, margine basali in longos aculeos producto: basi concavâ non porosâ, lineis radiantibus fortiter costatâ; spatio intercostali foraminibus minutis rotundatis sæpe duplici serie, cribrosè perforato.

Hab.--(?)

38. Balanus vestitus, Darwin. ('Balanidæ,' p. 286, Tab. 8, fig. 3.)

B. testâ subroseo-purpureâ aut albâ, membranâ aurantiacâ vestitâ: radiorum loco, meris fissuris: basi solidâ: scuto, cristâ adductoris acutâ curvatâ; musculi depressoris cristæ adsunt: tergi calcare brevi, truncato, 1/3 valvæ latitudine.

Hab.--In Australiâ et Novâ Zealandiâ.

39. Balanus imperator, Darwin. ('Balanidæ,' p. 288, Tab. 8, fig. 4.)

B. testâ internè imperatorio-purpureâ: parietibus crassis margine interno basali spinis et cristis irregularibus aspero: radiis angustis: basi admodùm tenui, solidâ: scuto cum musculorum depressorum rostralium et lateralium cristis: tergi calcare ad finem rotundato.

Hab.--In Australiâ.

40. Balanus flosculus, Darwin. ('Balanidæ,' p. 290, Tab. 8, fig. 5.)

B. testâ purpureâ aut sordide-albâ, parietum margine basali spinis et cristis irregularibus asperâ: radiis angustis aut nullis: basi quam tenuissimâ, ad speciem nullâ: scuto cum musculi depressoris lateralis cristis: tergo admodùm angusto, calcare acuminato.

Hab.--In Americæ merid. littore occid.

41. Balanus bisulcatus, Darwin. ('Balanidæ,' p. 293, Tab. 8, fig. 6.)

B. radiorum marginibus superioribus obliquis, lævibus; aciebus suturalibus lævibus: basi poris magnis perforatâ: scuto angusto, sulcis longitudinalibus 2 ad 4: tergi calcare brevissimo dimidiâ valvæ latitudine.

Foss. in Angliâ, et Galliâ et Belgio. "Miocenâ Formatione."

42. Balanus dolosus, Darwin. ('Balanidæ,' p. 295, Tab. 8, fig. 7.)

B. radiorum marginibus superioribus obliquis lævibus: aciebus suturalibus item lævibus: basi poris magnis perforatâ: tergi calcare non admodum brevi, 1/3 valvæ latitudine.

Foss. in Angliâ. "Pliocenâ, et miocenâ Formationibus."

43. Balanus unguiformis, J. de C. Sowerby. (Darwin, 'Balanidæ,' p. 296, Tab. 8, fig. 8.)

B. parietibus tenuibus, interdum poris perforatis: radiorum marginibus superioribus obliquis; aciebus suturalibus tenuissimè crenatis: basi solidâ: tergi calcare angusto, obtuso.

Foss. in Angliâ et Belgio. "Eocenâ Formatione."

44. Balanus varians, Darwin. ('Balanidæ,' p. 298, Tab. 8, fig. 9.)

B. parietibus modicè crassis; radiorum marginibus superioribus perobliquis; aciebus suturalibus pæne lævibus aut tenuiter crenatis: basi tenuiter porosâ: tergi calcare, parvo, angusto, obtuso.

Foss. in Patagoniâ.

45. Balanus inclusus, Darwin. ('Balanidæ,' p. 299, Tab. 8, fig. 10.)

B. testâ rufo-fuscâ: radiis latis, marginibus superioribus aut non obliquis aut modicè; aciebus suturalibus cum septis planè denticulatis: basi porosâ: scuto sine adductoris cristâ: tergi calcare subangusto.

Foss. in Angliâ et Germaniâ. "Miocenâ Formatione."

2. Sub-Genus--ACASTA.

1. Acasta spongites, Poli. (Darwin, 'Balanidæ,' p. 308, Tab. 9, fig. 1.)

A. parietibus carino-lateralibus ferè 1/6 parietum lateralium latitudine: superficie internâ parietum plerumque debiliter costatâ: scuti cristâ articulari ad extremitatem inferiorem abruptè præcisâ: tergi calcare truncato rotundato, ferè 1/3 valvæ latitudine.

Hab.--In Europâ et Africâ meridion.

2. Acasta sulcata, Lamarck. (Darwin, 'Balanidæ,' p. 310, Tab. 9, fig. 2.)

A. parietibus carino-lateralibus ferè 1/6 parietum lateralium latitudine: parietum superficie internâ plerumque fortiter costatâ: basis acie fortiter crenatâ: testæ orificio sub-exiguo: tergi calcare plerumque truncato, pæne 1/2 valvæ latitudine.

Hab.--In Australiâ.

3. Acasta cyathus, Darwin. ('Balanidæ,' p. 312, Tab. 9, fig. 3.)

A. parietibus carino-lateralibus ferè 1/4 parietum lateralium latitudine: radiis latioribus quam parietes: basi pæne planâ, exiguâ: tergi calcare truncato, 1/2 valvæ latitudine.

Hab.--In Madeirâ et Indiâ occid.

4. Acasta undulata, Darwin. ('Balanidæ,' p. 313, Tab. 9, fig. 4.)

A. testâ, ad speciem, ut in "A. spongites," sed majore: scuto externe striis longitudinalibus, sæpe binis, signato, sulcis intermediis latioribus: tergi calcare, pæne 1/2 valvæ latitudine.

Foss. in Angliâ. "Miocenâ Formatione."

5. Acasta glans, Lamarck. (Darwin, 'Balanidæ,' p. 314, Tab. 9, fig. 5.)

A. parietibus internè per-lævibus, marginibus lateralibus uniuscujusque testæ valvæ intùs prominentibus: basis acie rarò crenatâ, sed 6 dentibus introrsùs prominentibus instructâ: scuto longitudinaliter fortiter striato.

Hab.--In Australiâ.

6. Acasta lævigata, J. E. Gray. (Darwin, 'Balanidæ,' p. 315, Tab. 9, fig. 6.)

A. parietibus intùs per-lævibus, marginibus lateralibus uniuscujusque testæ valvæ internùs prominentibus: basis acie fortiter crenatâ, et 6 dentibus introrsùs prominentibus instructâ: scuto aut longitudinaliter tenuiter striato aut lævi.

Hab.--In Mari Rubro et Archipel. Philippino.

7. Acasta fenestrata, Darwin. ('Balanidæ,' p. 316, Tab. 9, fig. 7.)

A. testâ subrufâ, foraminibus magnis membranâ-tectis inter suturas suprà basin proximis, 6; parietibus carino-lateralibus 1/2 parietum lateralium latitudine: intùs, parietibus et basis acie lævibus: tergi cristâ articulari brevi prominente; calcare acuminato.

Hab.--In Archipel. Philippino.

8. Acasta purpurata, Darwin. ('Balanidæ,' p. 318, Tab. 9, fig. 8.)

A. testâ obscurè cæruleo-purpureâ, foraminibus parvis, membrana-tectis inter suturas suprà basin proximis, 6: tergi cristâ articulari per-brevi prominente; calcare admodum lato rotundato.

Hab.--In Sumatrâ et Archipel. Philippino.

9. Acasta sporillus, Darwin. ('Balanidæ,' p. 319, Tab. 9, fig. 9.)

A. testâ purpureo-fuscâ, parietibus intùs fortiter costatis et reticulatis: testæ valvis carino-lateralibus angustissimis, ad basin non extendentibus.

Hab.--In Sooloo Insulis, in Archipelago Indico orient.

3. Genus--TETRACLITA.

1. Tetraclita porosa, Linn. (Darwin, 'Balanidæ,' p. 328, Tab. 10, fig. 1.)

T. radiis (si qui rarò adsunt) angustis; etiam suturis sæpe nullis: testâ abruptè conicâ, superficie plerumque corrosâ, stalactitiferam speciem exhibente.

Hab.--In torridis et tepidis ubique maribus.

2. Tetraclita serrata, Darwin. ('Balanidæ,' p. 333, Tab. 10, fig. 2.)

T. testâ obscurè viridi-griseâ, costis longitudinalibus serratis angustis: radiis nullis: scuti cristis (articulari et adductoris) cavitatem usque ad apicem valvæ extendentem formantibus.

Hab.--In Africâ merid.

3. Tetraclita rosea, Krauss. (Darwin, 'Balanidæ,' p. 335, Tab. 10, fig. 3.)

T. testâ sordidè albâ, subroseo tinctâ; parietibus è serie unicâ magnarum tubarum formatis: radiis plerumque angustis: tergi calcare sub-brevi, lato.

Hab.--In Australiâ, et Africâ meridion.

4. Tetraclita purpurascens, W. Wood. (Darwin, 'Balanidæ,' p. 337, Tab. 11, fig. 1.)

T. testâ depressâ, pallidè purpureâ aut sordidè albâ, superficie longitudinaliter costatâ, aut corrosâ et granulatâ: radiis, aut etiam suturis, nullis, aut radiis planè formatis et latis, marginibus superioribus basi parallelibus: basi membranaceâ: scuto transversè elongato: tergo exiguo, calcare per-brevi, rotundato.

Hab.--In Australiâ.

5. Tetraclita costata, Darwin. ('Balanidæ,' p. 339, Tab. 11, fig. 2.)

T. testâ depressâ sub-albâ, plerumque costis longitudinalibus admodùm prominentibus, 10: radiis latis, marginibus superioribus basi parallelis: basi calcareâ: scuto externè longitudinaliter striato: tergi calcare brevi rotundato.

Hab.--In Archipel. Philippino.

6. Tetraclita vitiata, Darwin. ('Balanidæ,' p. 340, Tab. 11, fig. 3.)

T. testâ albâ, parte superiore plerumque roseo tinctâ; superficie irregulari; tubis parietalibus admodum irregularibus; radiis modicè latis, marginibus superioribus obliquis; alarum aciebus suturalibus percrassis crenatis: tergi calcare cum angulo basi-scutali non juncto; calcaris termino æquabiliter rotundato.

Hab.--In Australiâ septentr. et orient. et Archipel. Philippino.

7. Tetraclita cœrulescens, Spengler. (Darwin, 'Balanidæ,' p. 342, Tab. 11, fig. 4.)

T. testæ parte superiore viridi-cæruleo tinctâ, longitudinaliter costatâ; radiis modice latis, marginibus superioribus obliquis: scuto adductoris cristâ exiguâ, articulari admodùm prominente; ambabus ita conjunctis ut cavitatem parvam subcylindricam efficiant: tergi calcare cum angulo basi-scutali non juncto.

Hab.--In Archipel. Philippino et Oceano Pacifico.

8. Tetraclita radiata, De Blainville. (Darwin, 'Balanidæ,' p. 343, Tab. 11, fig. 5.)

T. testâ albâ costis longitudinalibus approximatis multis; radiis latis, marginibus superioribus leviter obliquis, intus porosis: tergi cristâ articulari suprà modum prominente; calcare cum angulo basi-scutali non juncto.

Hab.--In Indiâ occid. et Australiâ: sæpe navigiis suffixa.

4. Genus--ELMINIUS.

1. Elminius Kingii, J. E. Gray. (Darwin, 'Balanidæ,' p. 348, Tab. 11, fig. 6.)

E. testâ lævi; griseâ aut sordidè albâ; radiis latis, marginibus et aciebus lævibus: scuto, sine adductoris cristâ: tergi calcare ab angulo basi-scutali distincto: scuto et tergo interdum inter se calcifactis.

Hab.--In Americâ merid.

2. Elminius modestus, Darwin. ('Balanidæ,' p. 350, Tab. 12, fig. 1.)

E. testâ longitudinaliter plicatâ, subviridi aut albâ; radiis modicè latis, marginibus et aciebus lævibus: scuto sine adductoris cristâ: tergo angusto, calcare cum angulo basi-scutali confluente.

Hab.--In Australiâ.

3. Elminius plicatus, J. E. Gray. (Darwin, 'Balanidæ,' p. 351, Tab. 12, fig. 2.)

E. testâ longitudinaliter profundè plicatâ, corrosâ, alicubi aurantiacâ; radiis per-angustis, aciebus sinuosis, leviter dentatis: scuto cum adductoris cristâ.

Hab.--In Novâ Zealandiâ.

4. Elminius simplex, Darwin. ('Balanidæ,' p. 353, Tab. 12, fig. 3.)

E. testâ longitudinaliter costatâ, sordidè albâ; radiis angustissimis, marginibus et aciebus lævibus: scuto cum adductoris cristâ.

Hab.--In Australiâ.

5. Genus--PYRGOMA.

1. Pyrgoma Anglicum, Leach. (Darwin, 'Balanidæ,' p. 360, Tab. 12, fig. 4.)

P. testâ abruptè conicâ, purpureo-rubrâ; orificio ovato, angusto; basi porosâ, plerumque è coralio exsertâ: scuto et tergo subtriangularibus.

Hab.--In Magnâ Britanniâ et Europâ meridionali, et Insulis "Cape de Verde."

2. Pyrgoma Stokesii, Darwin. ('Balanidæ,' p. 361, Tab. 12, fig. 6.)

P. testâ modicè conicâ, pallidè purpureo-rubrâ; orificio ovato; basi non-porosâ, in coralium profunde conditâ: scuto et tergo subtriangularibus.

Hab.--In Indiâ occid.

3. Pyrgoma cancellatum, Leach. (Darwin, 'Balanidæ,' p. 362, Tab. 12, fig. 5.)

P. testâ circumferentiâ plerumque lobatâ: scuto elongato, adductoris cristâ longè infrà marginem basalem descendente, et ad rostralem finem in acumen quadratum producto: tergi calcare valvæ partem superiorem longitudine quadruplo superante.

Hab.--In Archip. Indico. orient. (?)

4. Pyrgoma conjugatum, Darwin. ('Balanidæ,' p. 364, Tab. 12, fig. 7.)

P. testâ pæne planâ, cristis approximatis radiantibus: scuto et tergo inter se sine suturâ calcifactis; scuto, adductoris cristâ infrà marginem basalem descendente, et ad terminum rostralem in acumen producto; tergi calcare superioris valvæ partis longitudinem ferè æquante.

Hab.--In Mari Rubro.

5. Pyrgoma grande, G. B. Sowerby, jun. (Darwin, 'Balanidæ,' p. 365, Tab. 13, fig. 1.)

P. testâ modicè convexâ, pæne lævi: scuto et tergo inter se sine suturâ calcifactis; scuto limbo occludente parvo instructo, adductoris cristâ infrà marginem basalem descendente: tergo quadrato, calcare nullo.

Hab.--In Archip. Indico orient.

6. Pyrgoma milleporæ, Darwin. ('Balanidæ,' p. 367, Tab. 13, fig. 2.)

P. testæ orificio angustè-ovato; vaginâ obscurè purpureâ: scuto multùm elongato: tergo triangulo, convexo, calcare nullo.

Hab.--In Archip. Philippino.

7. Pyrgoma dentatum, Darwin. ('Balanidæ,' p. 369, Tab. 13, fig. 3.)

P. scuto multùm elongato, cum prominentiâ articulari dentiformi: tergo convexo, irregulariter triangulo, interdum cum calcare imperfecto, et in superficie internâ dente introrsùs prominente; scuto et tergo limbo occludente instructis.

Hab.--In Mari Rubro.

8. Pyrgoma crenatum, G. B. Sowerby. (Darwin, 'Balanidæ,' p. 370. Tab. 13, fig. 4.)

P. scuto multùm elongato, adductoris cristâ infra marginem basalem reflexum descendente: tergi calcare lato depresso; scuto et tergo limbo occludente instructis.

Hab.--In Archip. Ind. orient et Philippino.

9. Pyrgoma monticulariæ, J. E. Gray. (Darwin, 'Balanidæ,' p. 372. Tab. 13, fig. 5.)

P. testâ irregulari, margine exteriore aspero; orificio minuto rotundo: scuto et tergo multum elongatis, inter se sine suturâ calcifactis, limbo occludente lato instructis.

Hab.--In Archip. Indico orient.

6. Sub-Genus--CREUSIA.

1. Creusia spinulosa, Leach, (Darwin, 'Balanidæ,' p. 376, Tab. 13, fig. 6, et Tab. 14, fig. 6.)

Hab.--In Maribus torridis.

7. Genus--CHELONOBIA.

1. Chelonobia testudinaria, Linn. (Darwin, 'Balanidæ,' p. 392, Tab. 14, fig. 1 et fig. 5, Tab. 15, fig. 1).

Ch. testâ conicâ, depressâ, gravi; radiis subangustis, depressis plerumque utrinque scrobiculatis.

Hab.--In tepidis et torridis ubique Maribus; testudinibus affixa.

2. Chelonobia caretta, Spengler. (Darwin, 'Balanidæ,' p. 394, Tab. 14, fig. 2.)

Ch. testâ globoso-convexâ, crassissimâ, gravissimâ; parte superiore tritâ, substriatâ; radiis aut non formatis aut admodum angustis; parietibus sine cavitatibus sursùm inter septa interrupta radiantia extendentibus.

Hab.--In Africâ occid. et Australiâ septent.; testudinibus affixa.

3. Chelonobia patula, Ranzani. (Darwin, 'Balanidæ,' p. 396, Tab. 14, fig. 3).

Ch. testâ abruptè conicâ, admodum lævi et tenui; orificio magno, ferè dimidium diametri basalis testæ superante; radiis latis, lævibus, leviter depressis.

Hab.--Mediterraneo; Africâ occid.; Indiâ occid.; Australiâ Crustaceis et molluscarum testis lævibus affixa.

[Sectio ††.]

8. Genus--CORONULA.

1. Coronula balænaris, Linn. (Darwin, 'Balanidæ,' p. 415, Tab. 15, fig. 2, Tab. 16, fig. 3 et 5.)

B. testâ multùm depressâ, costis longitudinalibus planatis, aciebus earum simplicibus; orificio hexagono-rotundato; radiis testæ ipsius crassitudinem pænè æquantibus; valvis opercularibus, 4.

Hab.--In Oceano meridionali.

2. Coronula diadema, Linn. (Darwin, 'Balanidæ,' p. 417, Tab. 15, fig. 3.)

C. testâ coroniformi, costis longitudinalibus convexis, aciebus earum crenatis; orificio hexagono; radiis modicè crassis, admodum latis; tergis nullis aut rudimentariis.

Hab.--In Oceano septentrionali.

3. Coronula reginæ, Darwin. ('Balanidæ,' p. 419, Tab. 15, fig. 5.)

C. testâ globoso-conicâ aut depressâ, costis longitudinalibus multùm planatis, aciebus earum crenatis, superficie striatâ, granulatâ; orificio hexagono; radiis tenuibus 1/5 testæ valvæ crassitudinem non superantibus; tergis nullis.

Hab.--In Oceano Pacifico.

4. Coronula barbara, Darwin. ('Balanidæ,' p. 421, Tab. 15, fig. 6).

C. testâ (probabiliter) coroniformi, costis longitudinalibus convexis, aciebus earum crenatis, superficie internâ et externâ cristis transversis asperâ; radiis modicè crassis; spatio inter radios et alas solidè impleto.

Foss.--In Angliâ, "Red Crag Formatione."

9. Genus--PLATYLEPAS.

1. Platylepas bissexlobata, De Blainville. (Darwin, 'Balanidæ,' p. 428, Tab. 17, fig. 1.)

P. testâ lineis transversis incrementi conspicuis; parietibus porosis; vaginâ ad dimidium parietum vix descendente.

Hab.--In Mediterraneo; Africâ occid.; Indiâ occid.; Australiâ septentrionali.

2. Platylepas decorata, Darwin. ('Balanidæ,' p. 429, Tab. 17, fig. 2.)

P. testâ costis longitudinalibus tenuibus, parte earum inferiore globulis minutis decoratâ; parietibus non porosis; membranâ basali pari cum testâ convexitate.

Hab.--In Oceano Pacifico.

10. Genus--TUBICINELLA.

1. Tubicinella trachealis, Shaw. (Darwin, 'Balanidæ,' p. 431, Tab. 17, fig. 3).

Hab.--In Oceano Pacifico meridionali.

11. Genus--XENOBALANUS.

1. Xenobalanus globicipitis, Steenstrup. (Darwin, 'Balanidæ,' p. 440, Tab. 17, fig. 4.)

Hab.--In Oceano Atlantico septentrionali.

Sub-Fam. CHTHAMALINÆ.

12. Genus--CHTHAMALUS.

1. Chthamalus stellatus, Poli. (Darwin, 'Balanidæ,' p. 455, Tab. 18, fig. 1.)

Ch. testâ albâ aut griseâ, plerumque multùm corrosâ et punctâ; radiis (si qui adsunt) angustis, aciebus suturalibus tenuissimè crenatis; tergo, musculi depressoris cristis infrà marginem basalem vix dependentibus.

Hab.--In Europâ; Americâ sept.; Braziliâ; Mari Rubro; Chinâ; Californiâ septent.

2. Chthamalus antennatus, Darwin. ('Balanidæ,' p. 460, Tab. 18, fig. 2.)

Ch. testâ conicâ, plerumque lævi; nisi profundè corrosâ, pallidè sordidè carneâ; suturis semper distinctis; radiis, si qui adsunt, aciebus suturalibus per-lævibus.

Hab.--In Australiâ.

3. Chthamalus cirratus, Darwin. ('Balanidæ,' p. 461, Tab. 18, fig. 4.)

Ch. testâ albâ aut griseâ; vaginâ et valvis opercularibus membranâ fimbriatâ plerumque vestitis; tergo, angulo basi-carinali dependente et acuminato.

Hab.--In Chiliâ, Peruviâ.

4. Chthamalus fissus, Darwin. ('Balanidæ,' p. 462, Tab. 18, fig. 6.)

Ch. testâ subfuscâ, plicatâ; orificio longitudine duplo majore quam latitudo; tergo triangulo, æquilaterali, marginibus basalibus et carinalibus leviter prominentibus.

Hab.--In Californiâ.

5. Chthamalus dentatus, Krauss. (Darwin, 'Balanidæ,' p. 463, Tab. 18, fig. 3).

Ch. testâ sordidè albâ, aut subfuscâ; suturis, dentibus inter se concurrentibus formatis; tergi margine carinali prominente.

Hab.--In Africâ.

6. Chthamalus Hembeli, Conrad. (Darwin, 'Balanidæ,' p. 465, Tab. 18, fig. 5.)

Ch. testâ obscurè rubro-purpureâ; suturis aut obliteratis aut dentibus inter se concurrentibus formatis; basi interdum per parietum inflectionem calcareâ factâ; scuto, sulcis duobus vel tribus ad mediam valvam deorsùm extendentibus.

Hab.--In Californiâ.

7. Chthamalus intertextus, Darwin. ('Balanidæ,' p. 467, Tab. 19, fig. 1.)

Ch. testâ (si benè conservetur) violaceo-purpureâ; suturis aut obliteratis aut ex interplicatis laminis obliquis formatis; basi membranaceâ, sed cingente projecturâ ex parietum marginibus basalibus inflexis formatâ: scuto et tergo inter se prorsus calcifactis.

Hab.--In Archip. Philippino.

8. Chthamalus scabrosus, Darwin. ('Balanidæ,' p. 468, Tab. 19, fig. 2.)

Ch. testâ (si benè conservetur) obscurè purpureo-fuscâ; suturis ex interplicatis laminis obliquis (sed raro benè) formatis; tergo, cum musculi depressoris fossâ profundâ angustâ, ad angulum basi-carinalem.

Hab.--In Americæ merid. littore merid. et occid.

13. Genus--CHAMÆSIPHO.

1. Chamæsipho columna, Spengler. (Darwin, 'Balanidæ,' p. 470, Tab. 19, fig. 3.)

Ch. suturis, nisi in recenter natis, plerumque et internè et externè obliteratis; tergo, cum depressoris musculi fossis parvis.

Hab.--In Australiâ.

2. Chamæsipho scutelliformis, Darwin. ('Balanidæ,' p. 472, Tab. 19, fig. 4.)

Ch. rostro per-exiguo, elongato, triangulo: testæ valvarum lateralium unâquæque cum foramine, et carinâ cum duobus similibus foraminibus; quæ 4 in columnas tubulares testaceas conducunt.

Hab.--In Chinâ (?)

14. Genus--PACHYLASMA.

1. Pachylasma giganteum, Philippi. (Darwin, 'Balanidæ,' p. 477, Tab. 19, fig. 5.)

P. testâ et operculo sordide albis; testæ valvâ laterali et carino-laterali alis similibus instructâ.

Hab.--In Mari Mediterraneo.

2. Pachylasma aurantiacum, Darwin. ('Balanidæ,' p. 480, Tab. 20, fig. 1.)

P. testâ aurantiaco tinctâ; ad speciem externam, quasi è 4 solùm testæ valvis formatâ, ideò quòd laterales, et carino-laterales valvæ utrinque obscurâ fissurâ solùm separantur.

Hab.--In Australiâ.

15. Genus--OCTOMERIS.

1. Octomeris angulosa, G. B. Sowerby. (Darwin, 'Balanidæ,' p. 483, Tab. 20, fig. 2.)

O. testâ sordidè albâ, asperâ, solidâ; alis crassis, aciebus suturalibus obtusè crenatis.

Hab.--In Africâ merid.

2. Octomeris brunnea, Darwin. ('Balanidæ,' p. 484, Tab. 20, fig. 3.)

O. testâ rubro-fuscâ depressâ, tenui, longitudinaliter sulcis tenuibus signatâ; tergi margine basali leviter in angulum flexâ.

Hab.--In Archip. Philippino.

16. Genus--CATOPHRAGMUS.

1. Catophragmus polymerus, Darwin. ('Balanidæ,' p. 487, Tab. 20, fig. 4.)

C. basi membranaceâ: sine appendicibus caudalibus.

Hab.--In Australiâ.

2. Catophragmus imbricatus, G. B. Sowerby. (Darwin, 'Balanidæ,' p. 490.)

C. basi calcareâ: cum appendicibus caudalibus.

Hab.--In Indiâ occident.

2. Fam. VERRUCIDÆ.

1. Genus--VERRUCA.

1. Verruca Strömia, Müller. (Darwin, 'Balanidæ,' p. 518, Tab. 21, fig. 1.)

V. scuto mobili, cristâ articulari inferiore dimidiam brevis cristæ articularis superioris latitudinem non æquante: testâ plerumque longitudinaliter sulcatâ.

Hab.--In Europâ; Mari Rubro.

2. Verruca lævigata, G. B. Sowerby. (Darwin, 'Balanidæ,' p. 520, Tab. 21, fig. 3.)

V. scuto mobili, cristâ articulari inferiore latiore quam brevis crista articularis superior; tergo mobili, latitudine majore quam altitudo, cristâ articulari superiore in terminum subacutum producto.

Hab.--In Americâ merid.

3. Verruca Spengleri, Darwin. ('Balanidæ,' p. 521, Tab. 21, fig. 2.)

Scuto mobili, cum adductoris musculi cristâ acutâ, rectâ, mediali; scuto immobili non majore quam immobile tergum.

Hab.--In Insulâ Madeirâ.

4. Verruca nexa, Darwin. ('Balanidæ,' p. 522, Tab. 21, fig. 5.)

V. testâ sub-rubrâ; scuto mobili cum cristis externis longitudinalibus fortiter prominentibus, præter cristas articulares; scuto immobili majore quam carina, adductoris musculi cristâ vel laminâ distinctâ nullâ.

Hab.--In Indiâ occid.

5. Verruca prisca, Bosquet. (Darwin, 'Balanidæ,' p. 525, Tab. 21, fig. 4.)

V. testâ lævi; scuti mobilis cristâ articulari inferiore aliquanto latiore quam superior.

Foss.--In Cretaceâ Formatione.

3. Fam. LEPADIDÆ.

1. Genus--LEPAS.

1. Lepas anatifera, Linn. (Darwin, 'Lepadidæ,' p. 73, Tab. 1, fig. 1, var.)

L. valvis aut lævibus aut delicate striatis; è duobus scutis, dextro solùm dente interno umbonali instructo; pedunculi parte superiore fuscâ.

Hab.--In Oceano, pæne ubique.

2. Lepas Hillii, Leach. (Darwin, 'Lepadidæ,' p. 77, Tab. 1, fig. 2.)

L. valvis lævibus; scutorum dentibus internis umbonalibus nullis; carinâ à cæteris valvis, furcâ etiam a scutorum basali margine, paululum distante; pedunculi parte superiore aut pallidâ aut aurantiacâ.

Hab.--In Oceano, pæne ubique.

3. Lepas anserifera, Linn. (Darwin, 'Lepadidæ,' p. 81, Tab. 1, fig. 4.)

L. valvis approximatis leviter sulcatis (tergis præcipuè); scuto dextro dente forti interno umbonali, lævo aut dente exiguo, aut merâ cristâ instructo; margine occludente arcuato, prominente; pedunculi parte superiore aurantiacâ.

Hab.--In Oceano, pæne ubique.

4. Lepas pectinata, Spengler. (Darwin, 'Lepadidæ,' p. 85, Tab. 1, fig. 3.)

L. valvis tenuibus, crassè sulcatis, sæpe pectinatis; scutorum cristâ prominente ab umbone ad apicem, juxta marginem occludentem, pertinente; furcæ carinalis cruribus inter angulos 135° et 180° divergentibus.

Hab.--In Oceano Atlantico, sept. et meridionali.

5. Lepas australis, Darwin. ('Lepadidæ,' p. 89, Tab. 1, fig. 5.)

L. valvis glabris, tenuibus, fragilibus; scutorum dentibus umbonalibus utrinque internis; carinæ parte superiore latâ, planâ, suprà furcam valdè constrictâ; furcæ cruribus latis, planis, tenuibus, acuminatis, intermedio margine non reflexo.

Hab.--In Oceano meridionali.

6. Lepas fascicularis, Ellis. (Darwin, 'Lepadidæ,' p. 92, Tab. 1, fig. 6.)

L. valvis glabris, tenuibus, pellucidis; carinâ rectangulè flexâ, parte inferiore in discum planum oblongum expansâ.

Hab.--In Oceano torrido et tepido, pæne ubique.

2. Genus--PŒCILASMA.

1. Pœcilasma Kæmpferi, Darwin. ('Lepadidæ,' p. 102, Tab. 2, fig. 1.)

P. valvis 5; carinæ basi truncatâ et cristatâ: scutorum dentibus internis umbonalibus fortibus: tergorum acumine basali truncato, margini occludenti pæne parallelo.

Hab. in Japaniâ.

2. Pœcilasma aurantia, Darwin. ('Lepadidæ,' p. 105, Tab. 2, fig. 2.)

P. valvis 5; carinæ basi truncatâ: scutis ovatis, margine basali per-brevi, dentibus parvis, internis, umbonalibus instructo: tergorum acumine basali perobliquè truncato.

Hab.--In Insulâ Madeirâ.

3. Pœcilasma crassa, J. E. Gray. (Darwin 'Lapadidæ,' p. 107, Tab. 2, fig. 3.)

P. valvis 5; carinæ termino basali in discum parvum infossum producto: scutis convexis, dentibus internis umbonalibus nullis: tergis pæne rudimentalibus, vix carinâ latioribus.

Hab.--In Insulâ Madeirâ.

4. Pœcilasma fissa, Darwin. ('Lepadidæ,' p. 109, Tab. 2, fig. 4.)

P. valvis 7; scuto utroque è duobus juxtapositis segmentis formato; segmento altero intus dentato: tergis brevibus, ter aut quater carinâ latioribus: carinæ termino basali in discum parvum angustum infossum producto.

Hab.--In Archipel. Philippino.

5. Pœcilasma eburnea, Hinds. (Darwin, 'Lepadidæ,' p. 112, Tab. 2, fig. 5.)

P. valvis 3; scutis acuminatis, ovatis; ad pedunculum pæne transversè spectantibus; dentibus internis umbonalibus fortibus: tergis nullis carinæ termino basali in discum amplum oblongum infossum producto.

Hab.--In Novâ Guineâ.

3. Genus--DICHELASPIS.

1. Dichelaspis Warwickii, J. E. Gray. (Darwin, 'Lepadidæ,' p. 120, Tab. 2, fig. 6.)

D. scutorum segmento basali duplo latiore quam segmentum occludens: tergorum parte inferiore paulò, latiore quam occludens scutorum segmentum.

Hab.--In Archipel. Indico orientali.

2. Dichelaspis Grayii, Darwin. ('Lepadidæ,' p. 123, Tab. 2, fig. 9.)

D. scutorum segmento basali angustiore quam segmentum occludens; longitudine pæne dimidiâ: tergis bipenniformibus, margine crenato, spinâ posticâ, manubrio angustiore quam occludens scutorum segmentum.

Hab.--In Oceano torrido, aut Indico, aut Pacifico.

3. Dichelaspis pellucida, Darwin. ('Lepadidæ,' p. 125, Tab. 2, fig. 7.)

D. valvarum singularum acuminibus superioribus et inferioribus vix intersecantibus: scutorum segmento basali multo angustiore quam segmentum occludens; longitudine ferè dimidia: tergis bipenniformibus, margine integro, manubrii acumine ad carinam flexo.

Hab.--In Oceano Indico.

4. Dichelaspis Lowei, Darwin. ('Lepadidæ,' p. 128. Tab. 2, fig. 8.)

D. scutorum segmento basali angustiore quam occludens segmentum, longitudine ferè 4/5: tergorum parte inferiori duplo latiore quam occludens scutorum segmentum.

Hab.--In Insulâ Madeirâ.

5. Dichelaspis orthogonia, Darwin. ('Lepadidæ,' p. 130, Tab. 2, fig. 10.)

D. scutorum basali segmento angustiore quam occludens segmentum; longitudine ferè dimidiâ; duorum segmentorum junctione calcareâ: tergorum prominentiis marginalibus inæqualibus 5: carinâ deorsum in parvo calyce lunato terminatâ.

Hab.--(?)

4. Genus--OXYNASPIS.

1. Oxynaspis celata, Darwin. ('Lepadidæ,' p. 134, Tab. 3, fig. 1.)

Hab.--Insulâ Madeirâ.

5. Genus--CONCHODERMA.

1. Conchoderma aurita, Linn. (Darwin, 'Lepadidæ,' p. 141, Tab. 3, fig. 4.)

C. capitulo duobus tubularibus quasi-auribus instructo, pone terga rudimentalia (sæpe nulla) positis: scutis bilobatis: carinâ nullâ, aut omnino rudimentali: pedunculo longo, a capitulo distincte separato.

Hab.--In Oceano, pænè ubique.

2. Conchoderma virgata, Spengler. (Darwin, 'Lepadidæ,' p. 146, Tab. 3, fig. 2.)

C. scutis trilobatis: tergis intùs concavis, apicibus introrsùm leviter curvatis: carinâ modicâ, leviter curvatâ: pedunculo in capitulum coalescente.

Hab.--In Oceano, pænè ubique.

3. Conchoderma Hunteri, Owen. (Darwin, 'Lepadidæ,' p. 153, Tab. 3, fig. 3.)

C. valvis angustis: scutis trilobatis, prominentiâ laterali non latiore quam inferior: tergorum parte superiore pæne rectangulè secundùm aperturæ marginem flexâ: carinâ valde arcuatâ: pedunculo brevi, in capitulum coalescente.

Hab.--In Oceano torrido, aut Indico, aut Pacifico.

6. Genus--ALEPAS.

1. Alepas minuta, Philippi. (Darwin, 'Lepadidæ,' p. 160, Tab. 3, fig. 5.)

A. aperturâ non prominente, capituli longitudinis vix tertiam partem æquante: scutis corneis, pæne absconditis: longitudine totâ ad quartam unciæ partem.

Hab.--In Mari Mediterraneo.

2. Alepas parasita, S. Rang. (Darwin, 'Lepadidæ,' p. 163.)

A. aperturâ non prominente, capituli longitudinis 2/3 æquante: scutis corneis: longitudine totâ ad 2 uncias.

Hab.--In Mari Mediterraneo et Oceano Atlantico septentrionale.

3. Alepas cornuta, Darwin. ('Lepadidæ,' p. 165, Tab. 3, fig. 6.)

A. aperturâ parvâ, leviter prominente: scutis nullis: capitulo plerumque tribus, parvis, compressis eminentiis secundum carinalem marginem instructo.

Hab.--In Insulis Indicis occidentalibus.

4. Alepas tubulosa, Quoy et Gaimard. (Darwin, 'Lepadidæ,' p. 169.)

A. aperturâ parvâ prominente et tubulosâ: scutis et prominentiis secundùm marginem carinalem, nullis.

Hab.--In Novâ Zealandiâ.

7. Genus--ANELASMA.

1. Anelasma squalicola, Lovén. (Darwin, 'Lepadidæ,' p. 170, Tab. 5, fig. 1-7.)

Hab.--In Mari septentrionali, squalis affixa.

8. Genus--ALCIPPE.

1. Alcippe lampas, Hancock. (Darwin, 'Balanidæ,' p. 530, Tab. 22, et Tab. 23, fig. 16-19.)

Hab.--Littoribus Anglicis, molluscis condita.

9. Genus--IBLA.

1. Ibla Cumingii, Darwin. ('Lepadidæ,' p. 183, Tab. 4, fig. 8.)

I. (fœm.) valvarum marginibus lateralibus, et superficie interiore, cæruleis; pedunculi spinis plerumque annulis cæruleo-fuscis.

Hab.--In Archipel. Philippino, et littore Burmah.

2. Ibla quadrivalvis, Cuvier. (Darwin, 'Lepadidæ,' p. 203, Tab. 4, fig. 9.)

I. (Herm.) valvis et pedunculi spinis sub-flavis; basali tergorum angulo, introrsùm spectanti, hebete, quia margo carinalis inferior longiùs quam mango scutalis prominet.

Hab.--In Australiâ meridionali.

10. Genus--SCALPELLUM.

Sectio † Carinæ umbone sub-centrali.

Sectio †† Carinæ umbone ad apicem posito.

[Sectio †.]

1. Scalpellum vulgare, Leach. (Darwin, 'Lepadidæ,' p. 222, Tab. 5, fig. 15.)

S. (Herm.) valvis 14, si rostrum pæne rudimentale includatur; sub-carinâ nullâ; lateribus superioribus inæqualiter ovatis.

Hab.--In maribus Europæ.

2. Scalpellum magnum, Darwin. ('Lepadidæ Fossiles,' p. 18, Tab. 1, fig. 1.)

S. valvis probabiliter 14, sub-carinâ nullâ; laterum carinalium et rostralium umbonibus liberè (sicut cornua) prominentibus, dimidiam seu tertiam partem longitudinis valvarum æquantibus.

Foss.--In "Coralline Crag Formatione," Angliâ.

3. Scalpellum ornatum, J. E. Gray. (Darwin, 'Lepadidæ,' p. 244, Tab. 6, fig. 1.)

S. (Fœm.) valvis 14, sub-rufis; sub-carinâ nullâ; lateribus superioribus quadranti-formibus, arcu crenâ profundâ notato.

Hab.--In Africâ meridionali.

4. Scalpellum rostratum, Darwin. ('Lepadidæ,' p. 259, Tab. 6, fig. 7.)

S. (Herm.) valvis 15; rostro per-magno; sub-carinâ præsente; laterum paribus quatuor; pari superiore pentagono.

Hab.--In Archipel. Philippino.

5. Scalpellum Peronii, J. E. Gray. (Darwin, 'Lepadidæ,' p. 264, Tab. 6, fig. 6.)

S. (Herm.) valvis 13; sub-carinâ præsente; laterum paribus tribus; pari superiore multùm elongato; pedunculi squamis calcareis nullis.

Hab.--In Australiâ.

6. Scalpellum Darwinianum, Bosquet. ('Monograph. Crust. Foss. de Limbourg,' Tab. 4, fig. 1-5.)

S. carinâ ad angulum 115° flexâ, umbone centrali, costis tenuibus ab umbone utrinque radiantibus; carinæ tectis et superioris et inferioris partis rectis, planis, lævibus.

Foss.--In Cretaceâ superiore Formatione.

7. Scalpellum Hagenovianum, Bosquet. (Idem, Tab. 4, fig. 13-16.)

S. carinæ umbone ad 1/6 totius ab apice longitudinis posito; carinæ tecto plano, utrinque sulcato; parietum et intra-parietum confluentium parte superiore solummodò cristis instructo ab umbone radiantibus.

Foss.--In Cretaceâ superiore Formatione.

8. Scalpellum radiatum, Bosquet.[158] (Idem, Tab. 4, fig. 17-18.)

[158] Scalpelli 4 aliæ species fossiles, ad secundam generis sectionem pertinentes, à Dom. Bosquet descriptæ et nominatæ sunt. Jam cum equidem, ubi valvæ disjunctæ reperiuntur, nomina specifica non nisi carinis (et interdùm scutis) tribuere soleam, S. pulchellum, Bosq., hic inserere non possum, cujus scuti aut carinæ fragmenta valdè imperfecta solùm reperta sunt. Scalpellum gracile, S. pygmæum, et S. radiatum, Bosq., omnia Scalpello maximo et ejus varietatibus tam propè associantur, ut, cum ipse specimina non viderim, characteres breves diagnosticos hic exhibere non audeam. Veruntamen, cum Dom. Bosquet se hujus rei penitus peritum se probaverit, longissimè abest ut in dubium vocare velim quin hæ species reverà distinctæ existant.

S. scuti superficie cristis tectâ, inter se aliquantùm distantibus, ab umbone radiantibus; scuti umbone propè medium marginis occludentis posito; termino superiore truncato, lato, non acuminato.

Foss.--In Cretaceâ superiore Formatione.

[Sectio ††.]

9. Scalpellum rutilum, Darwin. ('Lepadidæ,' p. 253, Tab. 6, fig. 2.)

S. (Fœm. an Herm.) valvis 14 sub-rufis; sub-carinâ nullâ; carinæ tecto plano, utrinque cristâ rotundatâ instructo, margine basali truncato. Lateribus superioribus latitudine duplo longioribus.

Hab.--(?)

10. Scalpellum villosum, Leach. (Darwin, 'Lepadidæ,' p. 274, Tab. 6, fig. 8.)

S. (Herm.) valvis 14; sub-rostro et sub-carinâ præsentibus; carinâ pæne rectâ; laterum paribus tribus, pari superiore triangulo.

Hab.--In maribus orientalibus.

11. Scalpellum quadratum, Dixon. (Darwin, 'Lepad. Foss.' p. 22, Tab. 1, fig. 3.)

S. tecto parietibusque carinæ planis, lævibus, simplicibus, margine basali fere rotundato. Lateribus superioribus quinque-lateralibus, lævibus.

Foss.--In "Eocenâ Formatione" Anglicâ.

12. Scalpellum fossula, Darwin. ('Lepad. Foss.' p. 24, Tab. 1, fig. 4.)

S. carinâ intra-parietibus instructâ; tecto utrinque costis magnis, tumidis, superne planatis, marginato; margine basali obtusè acuminato. Lateribus superioribus quinque-lateralibus, costis duabus modicis ab apice ad marginem basalem continuatis.

Foss.--In Cretaceâ superiore Formatione.

13. Scalpellum maximum, J. Sowerby. (Darwin, 'Lepad. Foss.' p. 26, Tab. 2, fig. 1-10.)

S. carinâ intra-parietibus instructâ; tecto subangulari vel subcarinato; margine basali rectangulariter acuto; totâ valvâ plus minusve introrsùm arcuatâ, sed margine interno ferè-recto; tecto transversè plus minusve convexo; superficie pænè lævi, striis paucis obsoletis longitudinalibus elevatis; tectum, parietes, et intra-parietes inter se costis plus minusve prominentibus separantur.

Var. typicum, (Tab. 2, fig. 1, 4, 5, 8.)

S. carinâ introrsùm leviter arcuatâ, latitudine valvæ altitudinem superante; tecto transversè leniter arcuato; parietibus intra-parietibusque angustis, superficie pæne lævi.

Var. cylindraceum, (Tab. 2, fig. 2.)

S. parte superiore carinæ liberè prominente, parte interiore intra-parietibus rotundatis, inflexis, itâ repletâ, ut pæne cylindrica fiat; superficie externâ lævi, tecto parietibusque pæne confluentibus.

Var. sulcatum, (Tab. 2, fig. 3.)

S. carinâ introrsùm valde arcuatâ, sub-carinatâ; valvæ latitudine circà dimidium altitudinis æquante, tecto transversè præruptè arcuato; parietibus intra-parietibusque latiusculis. Apice solidè repleto, liberè paululùm prominente; superficie externâ striis paucis, rotundatis, ad alterum vel utrumque latus costarum duarum tectum et parietes separantium.

Foss.--In Cretaceâ a superiore Formatione.

14. Scapellum lineatum, Darwin. ('Lepad. Foss.' p. 35, Tab. 2, fig. 11, 12.)

S. superficie totâ carinæ lineis tenuibus, rotundatis, longitudinalibus, proximis, microscopicis obtectâ; cristæ centralis costâ crassiore; costis duabus vel tribus tectum et parietes separantibus; latitudine valvæ circa dimidium altitudinis æquante; intra-parietibus latiusculis, nullâ costâ conspicuâ a parietibus separatis; apice solidè repleto, aliquantulum liberè prominente.

Foss.--In Cretaceâ inferiore Formatione.

15. Scapellum hastatum, Darwin. ('Lepad. Foss.' p. 37, Tab. 2, fig. 13.)

S. carinâ intra-parietibus, intrà paululùm positis, instructâ; valvâ totâ introrsùm valdè arcuatâ, margine interno non recto; margine basali acuto, lanceolato; valvâ tenui, lævi, tecto transversè leniter arcuato; parietibus à tecto vix disjunctis.

Foss.--In "Grey Chalk, Dover."

16. Scalpellum angustum, Dixon. (Darwin, 'Lepad. Foss.' p. 37, Tab. 1, fig. 2.)

S. carinâ angustâ, introrsùm valdè arcuatâ; tecto à parietibus rectangulè inflexis costâ, (ut videtur) disjuncto; intra-parietibus usque ad dimidium valvæ pertinentibus, deinde obliquè et abruptè truncatis; margine basali acutè cuspidato.

Foss.--In Cretaceâ Formatione.

17. Scalpellum quadricarinatum, Reuss. (Darwin, 'Lepad. Foss.' p. 38.)

S. carinâ intra-parietibus latis (ut videtur) instructâ; tecto transversè plano, lævi, costâ prominente utrinque marginato; margine basali abruptè truncato.

Foss.--In "Untern Pläner-Kalke, Bohemia."

18. Scalpellum trilineatum, Darwin. ('Lepad. Foss.' p. 38, Tab. 1, fig. 5.)

S. carinæ tecto transversè leniter arcuato, subcarinato, costâ centrali et costis duabus lateralibus, rotundatis, tumidis; parietibus angustis leviter concavis, rectangulè inflexis.

Foss.--In "Grey Chalk, Dover."

19. Scalpellum simplex, Darwin. ('Lepad. Foss.' p. 39, Tab. 1, fig. 9.)

S. carinâ lævi; parietibus angustissimis, rectangulè inflexis; tecto subcarinato, transversè mediocriter arcuato; margine basali rectangulè acuminato.

Foss.--In "Lower Greensand."

20. Scapellum arcuatum, Darwin. ('Lepad. Foss.' p. 40, Tab. 1, fig. 7.)

S. valvarum lineis angustis elevatis ab apice radiantibus: carinæ tecto transversè leniter arcuato, et parietibus rectangulè inflexis, leniter concavis, lævibus.

Foss.--In "Gault."

21. Scalpellum solidulum, Steenstrup. (Darwin, 'Lepad. Foss.' p. 42, Tab. 1, fig. 8.)

S. valvarum lineis latiusculis elevatis ab apice radiantibus. Carinæ parte superiori liberè prominente, et cristâ centrali, internâ, longitudinali instructâ.

Foss.--In Cretaceâ superiore Formatione; Scaniâ.

22. Scalpellum tuberculatum, Darwin. ('Lepad. Foss.' p. 43, Tab. 1, fig. 10.)

S. valvarum lineis tenuibus, tuberculatis, elevatis, ab apice radiantibus: carinæ tecto transversè leniter arcuato, et parietibus striatis: scuti umbone prope in medio marginis occludentis posito, costis duobus ab umbone ad angulum basi-lateralem, et ad basalis marginis medium decurrentibus.

Foss.--In Cretaceâ Formatione.

23. Scalpellum semiporcatum, Darwin. ('Lepad. Foss.' p. 44, Tab. 1, fig. 6.)

S. carinâ ignotâ: scuti costis duobus ab umbone ad angulum basi-lateralem et ad marginis basalis medium decurrentibus; superficie inter hanc costam et marginem occludentem lineis tenuibus, longitudinalibus, elevatis instructâ.

Foss.--In Cretaceâ superiore Formatione; Scaniâ.

24. Scalpellum (?) cretæ, Steenstrup. (Darwin, 'Lepad. Foss.' p. 45, Tab. 1, fig. 11.)

S. valvis lævibus tenuissimis: scuti umbone propè medium marginis occludentis posito; costis tribus obscuris ab umbone ad angulos tergo-lateralem et basi-lateralem, et ad medium marginis basalis decurrentibus: carinæ apice et margine basali acutis; distincti parietes absunt.

Foss.--In Cretaceâ Formatione.

11. Genus--POLLICIPES.

†. Scuta, aut lævia aut lineis incrementi tenuibus solùm notata.

A. Scuta, costâ ab apice ad centrum marginis basalis non decurrente.

B. Scuta, costâ, nonnunquam subobsoletâ, ab apice ad centrum marginis basalis decurrente.

††. Scuta, aut longitudinaliter aut transversè (i. e. secundum lineas incrementi) costata.

[Sectio †, A.]

1. Pollicipes cornucopia, Leach. (Darwin, 'Lepadidæ,' p. 298, Tab. 7, fig. 1.)

P. capitulo, valvarum duobus aut pluribus sub rostro verticillis instructo: valvis albis, aut glaucis: pedunculo, squamarum densis verticillis symmetricè dispositis.

Hab.--In Europâ.

2. Pollicipes elegans, Lesson. (Darwin, 'Lepadidæ,' p. 304.)

P. capitulo, valvarum duobus aut pluribus sub rostro verticillis instructo: valvis et pedunculi squamis rufo-aurantiacis: squamarum verticillis densis symmetricè dispositis.

Hab.--In Peruviâ et Mexico.

3. Pollicipes polymerus, G. B. Sowerby. (Darwin, 'Lepadidæ,' p. 307, Tab. 7, fig. 2.)

P. capitulo, valvarum duobus, tribus, aut pluribus sub rostro verticillis instructo; valvis sub-fuscis; lateribus à supremo ad infimum gradatim quoad magnitudinem positis; carinæ margine basali (introrsùm spectanti) ad medium excavato; pedunculi squamarum verticillis densis, symmetricè dispositis.

Hab.--In Californiâ et Oceano Pacifico meridionali.

4. Pollicipes spinosus, Quoy. (Darwin, 'Lepadidæ,' p. 324, Tab. 7, fig. 4.)

P. capitulo valvarum uno aut pluribus sub rostro verticillis instructo: laterum pari superiore vix inferioribus longiore: membranâ valvas tegente (post desiccationem) subfuscâ flavescente: pedunculi squamis inæqualibus, non symmetricis: verticillis longiusculè distantibus.

Hab.--Novâ Zealandiâ.

5. Pollicipes sertus, Darwin. ('Lepadidæ,' p. 327, Tab. 7, fig. 5.)

P. capitulo valvarum uno aut pluribus sub rostro verticillis instructo: laterum pari superiore vix inferioribus longiore: membranâ valvas tegente (post desiccationem) fusco rufescente obscuro: rostro dimidiam carinæ longitudinem æquante, superficiei internæ altitudine latitudinem plus duplo superante: pedunculi squamis inæqualibus, non symmetricis: verticillis longiusculè distantibus.

Hab.--Novâ Zealandiâ.

6. Pollicipes concinnus, J. Morris. (Darwin, 'Lepad. Foss.' p. 50, Tab. 3, fig. 1.)

P. scutis pæne quadratis, margine basali propè rostrum subconcavo, segmento tergo-laterali, è lineis incrementi, ut videtur, reflexis formato, lato, rotundato et prominente: tergis latis, pæne quadratis: carinæ margine basali, ut videtur, acuto.

Foss.--In 'Oxford Clay.'

7. Pollicipes ooliticus, Buckman. (Darwin, 'Lepad. Foss.' p. 51, Tab. 3, fig. 2.)

P. scutis triangulis; superficie undulatâ; margine basali rectangulè ad marginem rectum tergo-lateralem posito; segmentum tergo-laterale è lineis reflexis incrementi formatum deest. Carinâ pæne rectâ, semi-cylindricâ, margine basali quadrato.

Foss.--In 'Stonesfield Slate.'

8. Pollicipes Nilssonii, Steenstrup. (Darwin, 'Lepad.' Foss. p. 52, Tab. 3, fig. 11.)

P. scutis triangulis, planis: margine basali cum margine occludente angulum pæne rectum, cum margine recto tergo-laterali, angulum aliquanto minorem formante: deest segmentum tergo-laterale, è lineis incrementi reflexis formatum. Carinâ introrsùs admodùm arcuatâ, crassâ; marginis basalis mucrone obtuso.

Foss.--In Cretaceâ superiore Formatione; Scaniâ.

9. Pollicipes Hausmanni, Koch. (Darwin, 'Lepad. Foss.' p. 53, Tab. 3, fig. 3.)

P. scutis subtriangulis, angulo basi-laterali valde rotundato; apice producto; margine basali cum margine occludente angulum pæne rectum formante; internâ apicis superficie prominente, margineque tergali sulcato.

Foss.--In 'Hilsthon,' Germaniâ.

10. Pollicipes politus, Darwin. ('Lepad.' Foss. p. 54, Tab. 3, fig. 4.)

P. scutis ferè rhombicis, lævissimis; margine basali cum margine occludente angulum recto majorem formante; margine occludente projecturâ parietali, lineari, minutâ instructo; internâ apicis superficie concavâ.

Foss.--In 'Gault.' (?)

11. Pollicipes elongatus, Steenstrup. (Darwin, 'Lepad. Foss.' p. 55, Tab. 3, fig. 5.)

P. scutis pæne quadratis; margine occludente et parte inferiori marginis tergo-lateralis rectangulè ad marginem basalem positis; apice obtuso.

Foss.--In Cretaceâ Formatione albâ. Daniâ.

12. Pollicipes acuminatus, Darwin. ('Lepad. Foss.' p. 56, Tab. 3, fig. 6.)

P. scutis elongatis, triangulis; margine basali cum margine occludente angulum recto longè minorem formante; internâ apicis superficie concavâ.

Foss.--In Cretaceâ Formatione.

13. Pollicipes Angelini, Darwin. ('Lepad. Foss.' p. 56, Tab. 3, fig. 7.)

P. scutis elongatis, triangulis, margine basali propè angulum rostralem in prominentiam obliquè rotundatam producto; internâ apicis superficie prominente, margine occludente sulcato.

Foss.--In Cretaceâ superiore Formatione.

14. Pollicipes reflexus, J. Sowerby. (Darwin, 'Lepad. Foss.' p. 58, Tab. 3, fig. 8.)

P. scutis tenuibus, subovalibus; margine basali cum margine occludente angulum recto longè majorem formante; costâ obsoletâ rotundatâ ab apice ad angulum basi-lateralem decurrente, valvam in duas ferè æquales partes separante. Carinâ lineari, transversè abruptè arcuatâ; margine basali multum producto, apice truncato. Lateribus superioribus sub-pentagonis.

Foss.--In Angliâ: 'Eocenâ Formatione.'

[Sectio †, B.]

15. Pollicipes carinatus, Philippi. (Darwin, 'Lepad. Foss.' p. 60, Tab. 3, fig. 9.)

P. scutis crassiusculis ad formam trianguli æquianguli accedentibus; margine occludente externè costâ, humili firmato; costâ firmâ ab apice ad centrum marginis basalis decurrente; margine basali recto; angulo basi-laterali truncato, brevi; segmentum tergo-laterale ex lineis incrementi reflexis formatum, deest. Carinâ externè valdè carinatâ cum sulco laterali ad utrumque latus.

Foss.--In Form. Tertiariâ, Siciliâ.

16. Pollicipes glaber, Roemer. (Darwin, 'Lepad. Foss.' p. 61, Tab. 3, fig. 10.)

P. scutis subtenuibus, latiusculis, ad formam trianguli æquianguli accedentibus; margine basali non prorsus recto; tergo-laterali segmento e zonis incrementi reflexis formato, ubi (latissimum), reliquæ valvæ dimidium æquante: margine tergali apicis intùs sulcato. Carinæ margine basali obtusè acuminato. Lateribus superioribus triangulis, tertiam partem longitudinis tergorum æquantibus. Lateribus anticis inferioribus singulis costâ propè terminum marginis basalis decurrente.

Foss.--In Cretaceâ, super. et inferiore Formatione.

17. Pollicipes unguis, J. Sowerby. (Darwin, 'Lepad. Foss.' p. 64, Tab. 4, fig. 1.)

P. scutis incognitis, verisimiliter ut in P. glabro. Margine basali carinæ obtusè acuminato, sub-rotundato. Lateribus superioribus elongatis triangularibus, dimidium longitudinis tergorum superantibus. Lateribus anticis inferioribus costâ subcentrali instructis.

Foss.--In 'Gault.'

18. Pollicipes validus, Steenstrup. (Darwin, 'Lepad. Foss.' p. 68, Tab. 4, figs. 2 and 3.)

P. scutis crassis, angustis; margine occludente externè costâ rotundatâ forti firmato; intus prominentiâ rostrali infra marginem rectum basalam dependente; costâ ab apice ad marginem basalem propiùs ad rostralem quam ad basi-lateralem angulum accedente. Carinâ lævissimâ, transversè semicylindricâ; parte superiori liberè prominente, internè aut planâ aut cristâ centrali instructâ.

Foss.--In Cretaceâ sup. Formatione, Scaniâ et Maestricht.

19. Pollicipes Darwinianus, Bosquet. (Monographie Crust. Foss. de Limbourg, Tab. 1, fig. 8-16.)

P. scuti marginibus basali et occludente angulum solum 35° formantibus; intùs prominentiâ rostrali infra marginem basalem dependente; costâ ab apice ad marginem basalam propemodùm ad angulum rostralem accedente. Tergo pæne pentagono, intùs prominentiâ à medio marginis scutalis surgente.

Foss.--In Cretaceâ superiore Formatione.

20. Pollicipes dorsatus, Steenstrup. (Darwin, 'Lepad. Foss.' p. 69, Tab. 4, fig. 4.)

P. scutis crassis; ad formam trianguli æquianguli accedentibus; margine occludente externè costâ rotundatâ firmato; angulo basi-laterali latè truncato, dimidium longitudinis marginis basalis veri, æquante; tergo-laterali segmento ex lineis incrementi reflexis formato, angustissimo. Tergorum costâ rectâ, latâ, proclivi, ab apice ad angulum basalem decurrente; angulo basali scutum versùs, obliquè truncato.

Foss.--In Cretaceâ superiore Formatione, Daniâ.

[Sectio ††.]

21. Pollicipes mitella, Linn. (Darwin, 'Lepadidæ,' p. 316, Tab. 7, fig. 3.)

P. capitulo valvarum unico sub rostro verticillo instructo: laterum pari superiore (introrsum spectanti) inferiorum magnitudinem ter aut quater superante: lateribus inferioribus utrinque obtegentibus: pedunculi squamarum verticillis densis, symmetricè dispositis.

Hab.--In Insulis Indicis orientalibus.

22. Pollicipes striatus, Darwin. ('Lepad. Foss.' p. 70, Tab. 4, fig. 5.)

P. valvis longitudinaliter striatis: scutis sub-triangulis, margine tergo-laterali valdè arcuato et prominente; costâ obscurâ, rotundatâ, ab apice ad angulum basi-lateralem decurrente; internâ apicis superficie solidè repletâ, sine sulco manifesto.

Foss.--In Cretaceâ superiore Formatione, Angliâ.

23. Pollicipes semilatus, Darwin. ('Lepad. Foss.' p. 72, Tab. 4, fig. 6.)

P. valvis longitudinaliter et transversè costatis: scutorum margine basali brevi, recto, cum margine occludente angulum rectum formante; costâ parietali tenuissimâ ab apice, ad angulum prominentem basi-lateralem decurrente; hæc valvam in duas partes inæquales dividit, è quibus portio tergo-lateralis latior est.

Foss.--In Cretaceâ Formatione.

24. Pollicipes rigidus, J. Sowerby. (Darwin, 'Lepad. Foss.' p. 73, Tab. 4, fig. 7.)

P. valvis transversè costatis: scutorum margine basali recto, cum margine occludente angulum recto majorem formante; costâ angustissimâ, parietali, ab apice ad angulum basi-lateralem decurrente: tergis, costâ curvâ, parietali, ad angulum basalem decurrente instructis; apice basali in prominentiam parvam terminante, lateribus prominentiæ parallelis.

Foss.--In 'Gault.'

25. Pollicipes fallax, Darwin. ('Lepad. Foss.' p. 75, Tab. 4, fig. 8.)

P. valvis transversè costatis: scutis margine basali non recto, angulum pæne rectum cum margine occludente formante; costâ, parietibus obliquis, ab apice ad angulum basi-lateralem decurrente: tergis, costâ curvatâ, parietibus obliquis, ad angulum basalem latum, rotundatum, decurrente.

Foss.--In Cretaceâ superiore Formatione, Angliâ, Scaniâ, Hanoveriâ.

26. Pollicipes elegans, Darwin. ('Lepad. Foss.' p. 76, Tab. 4, fig. 9.)

P. valvis longitudinaliter et transversè striatis: scutorum margine basali recto, cum margine occludente angulum recto paulo majorem formante; costâ parietali, latiore quam pro solitâ incrementorum linearum latitudine, ab apice ad angulum basi-lateralem decurrente: tergorum costâ parietali, rectâ, ad apicem basalem, acuminatum decurrente.

Foss.--In Cretaceâ superiore Formatione, Scaniâ, Daniâ.

[Species aliquot quas, scutis incognitis, auctores a valvis insignibus nominârunt, hìc pro tempore solummodo iterum describuntur.]

27. Pollicipes Bronnii, F. Roemer. (Darwin, 'Lepad. Foss.' p. 77, Tab. 4, fig. 10.)

P. carinâ lævi, subcarinatâ, margine basali arcuato et turgido; totâ valvâ vel extrorsùm arcuatâ vel pæne rectâ; internè, costis duabus elevatis ad utrumque latus partis superioris liberè prominentis.

Foss.--In 'Upper Greensand,' et 'Hils-conglomerat.'

28. Pollicipes planulatus, J. Morris. (Darwin, 'Lepad. Foss.' p. 27, Tab. 4, fig. 11.)

P. tergis subrhombicis, latis, lævibus, apice basali latè truncato, latitudine dimidium longitudinis marginis occludentis æquante; apice basali truncato angulum rectum cum margine scutali formante; parte superiori marginis scutalis cuspidem latam, rotundatam, leviter prominentem formante.

Foss.--In 'Oxford Clay.'

12. Genus--LITHOTRYA.

1. Lithotrya dorsalis, G. B. Sowerby. (Darwin, 'Lepadidæ,' p. 351, Tab. 8, fig. 1 a′.)

L. scutis terga angustè obtegentibus: carinâ intùs concavâ; rostro, duorum aut trium squamarum subjacentium latitudinem æquante: lateribus, squamarum quinque subjacentium longitudinem æquantibus, superficie internâ angustè ellipticâ: pedunculi squamis superioribus verticillum secundum minus duplo superantibus.

Hab.--Insulis Indicis occidentalibus.

2. Lithotrya cauta, Darwin. ('Lepadidæ,' p. 356, Tab. 8, fig. 3.)

L. scutis terga amplè obtegentibus: carinâ intus concavâ: rostro, squamarum subjacentium latitudinem vix æquante: lateribus, squamas subjacentes sesquitertio superantibus, superficie internâ latè ellipticâ: pedunculi squamis superioribus verticillum secundum pæne quadruplo superantibus.

Hab.--In Australiâ.

3. Lithotrya Nicobarica, Reinhardt. (Darwin, 'Lepadidæ,' p. 359, Tab. 8, fig. 2.)

L. scutis terga angustè obtegentibus: carinæ cristâ internâ tenui in parte superiore positâ: rostro conspicuo, squamarum sex subjacentium latitudinem æquante: lateribus, superficie internâ triangulâ squamarum septem subjacentium latitudinem æquantibus.

Hab.--In Insulis Nicobaricis et Timor.

4. Lithotrya rhodiopus, J. E. Gray. (Darwin, 'Lepadidæ,' p. 363, Tab. 8, fig. 4.)

L. scutis terga amplè obtegentibus: carinæ cristâ internâ tenui, in parte superiore positâ: lateribus, superficie internâ symmetricè et latè ovatâ, carinæ latitudinis plus quam tertiam partem æquantibus: tergorum basali apice tenui, et angulo carinali producto: rostro et pedunculo ignotis.

Hab.--(?)

5. Lithotrya truncata, Quoy. (Darwin, 'Lepadidæ,' p. 366, Tab. 9, fig. 1.)

L. scutis in profundam tergorum plicam insertis: carinæ cristâ centrali prominente et rotundatâ in parte superiore: rostro et lateribus rudimentalibus, carinæ latitudinis quindecimam fere partem æquantibus.

Hab.--In Arch. Philippino et Mari Pacifico.

6. Lithotrya Valentiana, J. E. Gray. (Darwin 'Lepadidæ,' p. 371, Tab. 8. fig. 5.)

L. scutis in profundam tergorum plicam insertis: tergorum opposito superiore margine, plicâ alterâ æquè profundâ instructo: carinæ cristâ prominente centrali, marginibus quadratis, in parte superiore: rostro rudimentali: lateribus et pedunculo ignotis.

Hab.--In Mari Rubro.

13. Genus--LORICULA.

1. Loricula pulchella, G. B. Sowerby, jun. (Darwin, 'Lepad. Foss.' p. 81, Tab. 5.)

Foss.--In Cretaceâ inferiore Formatione.

ORDO II. ABDOMINALIA.

1. Genus--CRYPTOPHIALUS.

1. Cryptophialus minutus, Darwin. ('Balanidæ,' p. 566, Tab. 23 et 24.)

Hab.--In littore occidentali Americæ meridionalis.

ORDO III. APODA.

1. Genus--PROTEOLEPAS.

1. Proteolepas bivincta, Darwin. ('Balanidæ,' p. 589, Tab. 24 et 25.)

Hab.--In insulis Indicis occidentalibus.

DESCRIPTION OF PLATES.

PLATE 1.

BALANUS TINTINNABULUM.

Fig. a, b, and f (upper shell), Balanus tintinnabulum,--var. communis. c and f (part of shell), " " " validus. d, " " " " coccopoma. e, " " " " concinnus. f (part of shell), " " " validus. g, " " " " zebra. h, " " " " crispatus. i, " " " " spinosus. k, " " " " occator. l, " " " " d'Orbignii.

PLATE 2.

Genus--BALANUS.

Fig. 1 a, Balanus tintinnabulum,--var. communis, scutum. 1 b, " " " occator " 1 c, 1 d, and 1 e, " " " communis " 1 f, " " " coccopoma " 1 g, " " " concinnus " 1 h, (magnified) " " (young) " vesiculosus " 1 i, and 1 k, " " " communis, tergum. 1 l, " " " coccopoma " 1 m,and 1 n, " " " d'Orbignii " 1 o, " " " coccopoma " 2 a, 2 b, 2 c, 2 d, Balanus tulipiformis, scutum and tergum, external and internal views of. 3 a, 3 b, 3 c, 3 d, Balanus psittacus, scutum and tergum, external and internal views of. 4 a, 4 b, Balanus Capensis, scutum and tergum, internal view of. 5 a, 5 b, Balanus nigrescens " " 6 a, Balanus decorus, scutum, internal view; 6 b, tergum, external view. 7 a, Balanus vinaceus, scutum, internal view; 7 b, do. external view; 7 c, tergum, external view; 7 d, basal edge of the parietes of one of the compartments, showing the cancellated structure of the inner lamina.

PLATE 3.

Genus--BALANUS.

Fig. 1 a, Balanus Ajax; 1 b, scutum external; 1 c, tergum external; and 1 d, scutum, internal view. 2 a, 2 b, Balanus stultus, scutum and tergum, external views; 2 c and 2 d, scutum, internal and external views. 3 a, Balanus calceolus; 3 b, variety; 3 c, scutum, internal view; 3 d, tergum, internal view; 3 e, spur of tergum toothed. 4 a, Balanus galeatus; 4 b, 4 c, scutum and tergum, internal view. 5 a, 5 b, Balanus cymbiformis, scutum and tergum, internal view. 6 a, Balanus navicula; 6 b, 6 c, scutum and tergum, internal view; 6 d, scutum, external view. 7 a, Balanus trigonus; 7 b and 7 c, scutum, external views, two varieties; 7 d, scutum, internal view; 7 e and 7 f, tergum, external views, two varieties.

PLATE 4.

Genus--BALANUS.

Fig. 1 a and 1 b, Balanus spongicola, external views of scutum and tergum; 1 c, var. of the tergum, from a specimen from the Cape of Good Hope; 1 d, var. of the tergum from the West Indies. 2, Balanus lævis. 2 a, " " fossil, elongated var., showing lower part of basal cup filled up with a cancellated mass. 2 b and 2 c, " " scutum, external and internal view of. 2 d and 2 e, " " scutum (variety), internal and external view of. 2 f, " " scutum (variety), external view. 2 g, " " tergum, external view. 3 a, Balanus perforatus, scutum, internal view; 3 b, tergum, internal view; 3 c, tergum, var. external view. 4 a, Balanus concavus (var. from Panama), scutum, internal view; 4 b, scutum, external view; 4 c, tergum, external view; 4 d, tergum, fossil, Coralline Crag; 4 e, tergum, fossil, Italy.

PLATE 5.

Genus--BALANUS.

Fig. 1 a, Balanus perforatus,--var. angustus. 1 b, " " " Cranchii. 1 c, " " " mirabilis. 1 d, " " " fistulosus. 2 a, " amphitrite,--var. venustus. 2 b, " " var. cirratus. 2 c, " " " pallidus. 2 d, " " " Stutchburii. 2 e, " " " communis. 2 f, " " " niveus. 2 g, " " " obscurus. 2 h, " " scutum, var. communis. 2 i, " " " " Stutchburii. 2 k, " " tergum, " pallidus. 2 l, " " " " communis. 2 m, 2 n, and 2 o," " var. Stutchburii. 3 a, Balanus pœcilus, scutum, internal view; 3 b, tergum, external. 4 a, Balanus eburneus, scutum, external view; 4 b, tergum, external; 4 c, scutum, internal; 4 d, tergum (var.), internal.

PLATE 6.

Genus--BALANUS.

Fig. 1 a, Balanus improvisus; 1 b, scutum, internal; 1 c, tergum, external view. 2 a, Balanus nubilus, scutum, internal view; 2 b, tergum, ditto; 2 c, tergum, external view. 3 a, 3 b, Balanus corrugatus, scutum and tergum, internal view. 4 a, Balanus porcatus; 4 b and 4 c, scutum and tergum, internal views; 4 d, tergum external; 4 e, basal edge of the parietes of wall of shell. 5 a, Balanus patellaris; 5 b, scutum, internal; 5 c, tergum, external. 6 a, Balanus crenatus. 6 b, " " smooth var. 6 c, " " elongated var. 6 d and 6 e, " scutum and tergum, external views. 6 f and 6 g, " " " internal views.

PLATE 7.

Genus--BALANUS.

Fig. 1 a, Balanus glandula, scutum, internal; 1 b, tergum, external. 2 a, Balanus balanoides; 2 b, portion of basal edge of parietes of a compartment; 2 c, tergum; 2 d, tergum, var. 3 a, Balanus cariosus; 3 b, portion of basal edge of parietes of a compartment; 3 c, scutum, internal view of; 3 d, tergum, internal; 3 e, tergum, external view. 4 a, Balanus declivis, lateral view, with basal membrane removed; 4 b, rostrum (to left hand), two lateral compartments, and carina; 4 c and 4 d, scutum and tergum, external views. 5 a, Balanus Hameri; 5 b, scutum, internal view; 5 c, tergum, external view. 6 a, Balanus amaryllis; 6 b, scutum, internal; 6 c, tergum, external view. 7 a, Balanus allium; 7 b and 7 c, scutum, external and internal views; 7 d, tergum, external. 8 a, Balanus cepa, scutum, internal; 8 b, scutum, external; 8 c, tergum, external view.

PLATE 8.

Genus--BALANUS.

Fig. 1, Balanus quadrivittatus. 2 a, Balanus terebratus, part of basis seen from the outside; 2 b, the same, seen from within. 3 a, Balanus vestitus, scutum, internal view; 3 b, tergum, external view. 4 a, Balanus imperator, scutum, internal view; 4 b, tergum, external view; 4 c, portion of basal edge of wall of the shell. 5 a, Balanus flosculus. 5 b, " " var. sordidus. 5 c, " " scutum, internal view. 5 d, " " " " var. 5 e and 5 f, " tergum, internal and external views of. 6 a, Balanus bisulcatus, scutum, external view; 6 b, tergum, external view; 6 c, scutum, internal view. 7, Balanus dolosus, tergum, external view. 8 a, Balanus unguiformis, scutum, internal view; 8 b, tergum, do. 9, Balanus varians, tergum, external view. 10 a, Balanus inclusus. 10 b, " " var. that has been attached to a branch of a coralline. 10 c, " " " seen from beneath, showing the narrow furrowed basis and wide lateral compartments; the other four compartments, namely, the two carino-lateral, the carina, and rostrum, being of very small size.

PLATE 9.

Sub-Genus--ACASTA.

Fig. 1 a, Acasta spongites; 1 b, scutum, external view; 1 c, scutum, internal; 1 d, tergum, internal. 2 a, Acasta sulcata; 2 b, var., lateral compartment of; 2 c and 2 d, terga, internal views of two varieties. 3 a, Acasta cyathus; 3 b and 3 c, scutum and tergum, internal views. 4, Acasta undulata, scutum, external view. 5 a, Acasta glans, basis seen from within; 5 b, compartments of a smaller specimen, seen from within; carina on the right-hand, cut into two; carino-lateral and lateral compartments to the left-hand; 5 c, tergum, internal view. 6 a, Acasta lævigata, tergum, internal view; 6 b, another var. 7 a, Acasta fenestrata; 7 b, scutum, and 7 c, tergum, internal views. 8 a, Acasta purpurata; 8 b, scutum; 8 c, tergum, internal views. 9 a, Acasta sporillus; 9 b, carino-lateral compartment (almost rudimentary) and lateral compartment, seen from within; 9 c and 9 d, scutum and tergum, seen from within.

PLATE 10.

Genus--TETRACLITA.

Fig. 1 a, Tetraclita porosa, var. communis. 1 b, " " " rubescens. 1 c, " " " nigrescens. 1 d, " " " elegans. 1 e, " " " communis, young, with radii developed. 1 f, " " " patellaris. 1 g, " " basal edge of wall of shell. 1 h, " " basal edge of wall of shell, var. elegans, showing also the structure of one of the rudimentary radii or sutures. 1 i, " " internal view of scutum; 1 k, do. of tergum; 1 l, do. of scutum, var.; 1 m, do. of tergum, var. 2 a, Tetraclita serrata; 2 b, portion of external surface of wall, low down, near basis; 2 c and 2 d, scutum and tergum, internal views. 3 a, Tetraclita rosea, scutum; 3 b, tergum; 3 c, whole shell; 3 d, basal edge of wall of shell.

PLATE 11.

Genera--TETRACLITA AND ELMINIUS.

Fig. 1 a, Tetraclita purpurascens, var. with surface disintegrated, and with the sutures united and obliterated. 1 b, Tetraclita purpurascens, var. well preserved, with the radii developed; 1 c and 1 d, var. scutum and tergum, internal views. 2 a, Tetraclita costata; 2 b and 2 c, scutum and tergum. 3 a, Tetraclita vitiata; 3 b, basal edge of portion of wall; 3 c and 3 d, scutum and tergum, internal views of; 3 e, tergum, internal view, var. 4 a, Tetraclita cœrulescens; 4 b, scutum and tergum united, external view; 4 c and 4 d, scutum and tergum, internal views. 5 a, Tetraclita radiata; 5 b, scutum and tergum united, external view; 5 c and 5 d, scutum and tergum, internal views. 6 a, Elminius Kingii; 6 b and 6 c, scutum and tergum, internal views of; 6 d, tergum, var. external view of; 6 e, tergum, another var. internal view of.

PLATE 12.

Genera--ELMINIUS AND PYRGOMA.

Fig. 1 a, Elminius modestus; 1 b, scutum, internal view; 1 c, tergum, internal view; 1 d, do., tergum, var.; 1 e, do., tergum, var. 2 a, Elminius plicatus; 2 b, basal edge of portion of wall of shell; 2 c and 2 d, scutum and tergum, internal views of; 2 e and 2 f, scutum and tergum, internal views of, var. 3, Elminius simplex; shell. 4 a, Pyrgoma Anglicum; 4 b and 4 c, scutum and tergum, internal views. 5 a, Pyrgoma cancellatum, shell, seen from above; 5 b, shell seen on the under side; 5 c and 5 d, scutum and tergum, external views; 5 e and 5 f, scutum and tergum, internal views of. 6, Pyrgoma Stokesii, shell imbedded in coral. 7 a, Pyrgoma conjugatum, shell, external view of; 7 b, scutum and tergum, calcified together, seen from the outside; 7 c, do., internal view of.

PLATE 13.

Genera--PYRGOMA AND CREUSIA.

Fig. 1 a, Pyrgoma grande; 1 b, scutum and tergum, calcified together, external view of; 1 c, scutum and tergum, internal view of; 1 d, the two scuta and terga, external view, seen from above, having their natural position, when closed. 2 a, Pyrgoma milleporæ, shell viewed from above; 2 b, internal view of, showing the sheath; 2 c, scutum and tergum, united, external view of; 2 d, scutum, var. external view of; 2 e, scutum, internal view of; 2 f, tergum, internal view of. 3 a, Pyrgoma dentatum shell, external view of; 3 b, scutum, var. 1, external view of; 3 c, tergum, var. 1, external view of; 3 d, tergum, var. 2, external view of; 3 e, scutum, var. 3, external view of; 3 f, tergum, var. 3, external view of; 3 g, scutum and tergum, var. 1, joined together, internal view of. 4 a, Pyrgoma crenatum, scutum, external view of, showing the great depending adductor plate and large occludent ledge; 4 b, external view of. 5 a, Pyrgoma monticulariæ, external view of; 5 b, another specimen, internal view of; 5 c, another specimen, external view of; 5 d, portion of circumference of shell, viewed externally, much magnified, showing the outer lamina, and the irregular, longitudinal septa; 5 e, another specimen of the same, with the longitudinal septa more regular; 5 f, scutum and tergum completely calcified together, external view of. 6 a, Creusia spinulosa, shell, seen from above. 6 b, 6 c, Creusia spinulosa, var. 1, scutum and tergum, internal view of; 6 d, scutum and tergum, joined together, external view of. 6 e, 6 f, 6 g, Creusia spinulosa, var. 2, 6 e, scutum, internal view; 6 f, tergum, internal view of; 6 g, tergum, of another specimen, internal view of. 6 h, Creusia spinulosa, var. 3, scutum and tergum joined together, external view of.

PLATE 14.

Genera--CREUSIA AND CHELONOBIA.

Fig. 6 i, 6 k, 6 l, Creusia spinulosa, var. 4, 6 i, tergum, external view; 6 k, the same, from another individual; 6 l, the same, internal view. 6 m, Creusia spinulosa, var. 5, tergum, external view. 6 n, 6_o_, 6_p_, 6_q_, Creusia spinulosa, var. 6, 6 n, scutum, external view of; 6 o, tergum of same individual, external view of; 6 p, scutum of another individual, external view of; 6 q, tergum of latter, external view of. 6 r, Creusia spinulosa, var. 7, scutum, internal view of. 6 s, Creusia spinulosa, var. 9, scutum and tergum, calcified together, external view. 6 t, Creusia spinulosa, var. 10, scutum and tergum, calcified together, external view. 6 U, Creusia spinulosa, var. 11, shell seen from above; 6 u, scutum and tergum, calcified together, external view.

Fig. 1 a, Chelonobia testudinaria, shell seen from above; a specimen has been chosen, with some of the radii smooth, and others more or less notched; 1 b, scutum, internal view of; 1 c, tergum, internal view of; 1 d, scutum and tergum, joined together, external view of. 2, Chelonobia caretta, shell seen from above. 3 a, Chelonobia patula, shell seen from above; 3 b, tergum, external view of. 4, Carina of Chelonobia patula, seen from within; a a, outer lamina of wall, joined by the longitudinal septa to b, the inner lamina; e c e, sheath, descending to the base of shell, with the middle part largely hollowed out; the upper part of the sheath, above d d, is transversely marked by the lines of attachment of the opercular membrane; d, d, alæ. 5, View of the edge of the radius of the rostrum of Chelonobia testudinaria. a, a, inner portion of radius. b, thick outer lamina of the radius, transversely pitted; beneath this pitted portion, which forms only the outer surface of the radius, and distinct from the inner portion a, the arborescent and dentated sutural edges of this outer lamina are seen. c, outer lamina of wall of compartment. d, the exterior septum, connecting the outer lamina of the wall to the inner lamina; the basal edge of the inner lamina of the wall is seen beneath and without the lower end of the inner portion (a) of the radius.

PLATE 15.

Genera--CHELONOBIA AND CORONULA.

Fig. 1, Transverse section of shell of Chelonobia testudinaria. B A B, Compound rostrum: A being the true rostrum. B B, the rostro-lateral compartments, which normally, in the Balaninæ, are quite confounded with the true rostrum: the sutures separating these three compartments are not continued through the outer lamina. C, left-hand lateral compartment. D, left-hand carino-lateral compartment. E, carina. S S, Sutures, six in number, separating the six compartments. a, outer lamina of wall of compartment, whence the radiating, longitudinal septa (left unshaded) arise, and at the opposite end blend into the indistinct inner lamina, viz. b, (see fig. 4, in last plate.) c′, sheath. d, ala, forming, as usual, part of the sheath. e, inner portion of the radius. f, f, outer lamina of the radius (see b, in fig. 5, in last plate), of great thickness, and externally deeply pitted;--the sharp ridges between the pits, produce in the section the points, such as that marked by the outer f. 2, Coronula balænaris, shell seen from above. 2 a, " " section of one of the transverse circumferential loops, formed by the folded wall of a compartment. The wall itself is formed of an outer and inner lamina, with longitudinal septa. The internal surfaces of the loop-part are connected by special shelly plates or longitudinal septa. 2 b, " " scutum and tergum united together by the opercular membrane (with horny ridges), seen from the inner side. 3, Coronula diadema, shell, seen from the outside; 3 a, scutum and tergum joined together by the opercular membrane, seen from the outside; 3 b, scutum cleaned and enlarged, seen from the inside. 4, Section, in a vertical plane, through the skin of a whale, on which a Coronula diadema had been attached, but has been wholly removed: the two curved, horn-like projections occupied two of the eighteen cavities on the under side of the shell, formed by the folded walls: the blacker part is the epidermis; the lighter part is the yellowish fibrous tissue of the skin under the epidermis. 5, Coronula reginæ, shell seen from the outside. 6, Coronula barbara, internal view of the basal margin and inside of one of the compartments, exhibiting the circumferential transversely looped ends of the folds of the wall, with the inner surface transversely wrinkled. 7-9, diagrams, showing how one of the circumferential transverse loops of the wall becomes divided into two transverse loops, thus giving rise to another fold in the wall. 10, diagrams, showing how the wall of the young shell in Coronula, from being (a) simply sinuous, becomes deeply folded (b); the folds lastly (c) expanding transversely at their ends, thus giving rise to the circumferential transverse loops, as in fig. 7.

PLATE 16.

Genus--CORONULA.

Fig. 1, rostrum, viewed from the inner side, of Coronula diadema. a, sheath, marked transversely in the upper part by the attachment of the opercular membrane. b, furrow on each side of (a), receiving the edges of the thick alæ of the adjoining lateral compartments. c′′, special plate, on which the alæ on their outer sides rest. d, radius, on the edge it may be just seen to consist of an outer layer (the normal radius), and a much thicker inner part (the pseudo or complementary radius) formed of oblique denticulated septa. e e′ e′′, basal edge of wall, which from its commencement at e, or e′′ can be followed, folding up to near the basal edge of the sheath, to its termination at e′′ or e. f, serrated lines of junction between the folds of the wall. 2, Lateral compartment of C. diadema, seen laterally, on a smaller scale than last fig., but taken from the same shell; letters of reference the same: this figure, if the ala a′ were removed, would do for a lateral view of the rostrum, or fig. 1. a, sheath, much foreshortened. a′, ala (therefore also part of sheath), and the edge of which fits into b of fig. 1. b, furrow receiving edge of ala of the adjoining carino-lateral compartment. c′′, special plate, seen edgeways. d, radius, the division into two parts, viz., the thin outer normal radius, and the under pseudo or complementary radius here shown (rather exaggerated) plainer than in fig. 1. e, basal edge of wall; to the right hand the three folds at their inner ends are seen obliquely, one behind the other: these are seen directly in front in fig. 1. 3, lateral compartment of C. balænaris, seen laterally; letters of reference the same as in last fig., but c′′ not introduced for this plate is barely developed, and only in the lower part, and is attached to the radius: g g points where fresh folds have been formed in the walls along the lines of suture, as may be seen in the outline of the wall in fig. 5. 4, lateral compartment of C. reginæ, seen laterally; letters of reference the same as in the last two figures. 5, Coronula balænaris, outline of the basal margin of the folded walls: s, s, the six sutures. The wall can be continuously followed from one end of a suture to the next suture. 6, Coronula diadema; small portion of the external surface of the wall, close to the basal edge, highly magnified; a, outer lamina, not extending down to the basal edge; b, inner lamina; c, projecting longitudinal septa. 7, Coronula diadema; transverse section through the upper part of the shell, showing the rostrum and the two adjoining lateral compartments (and the alæ of the carino-lateral compartments), all supposed to be a little separated from each other, so that the sutures, s s, are shown by white lines. A A A, rostrum. C C, lateral compartments. D D, carino-lateral compartments, of which only the alæ (a′) are shown. Of the letters in italics, those which occur in figs. 1, 2, 3, 4, 5, refer all to the same parts, viz.:-- a, sheath, continuous with (a′) the alæ, where such occur. c′′, special plate on which the alæ rest. d, radius, divided into a thin outer normal radius, and the inner complementary portion, the latter shaded by convex lines of growth. d′ is a special tube (seen only as a black dot) for a thread of corium. e, folded walls. f, junction of the folded walls (see f, in fig. 1) leading into the cavities (f′) open beneath, and filled up by the epidermis (see Pl. 15, fig. 4) of the whale. h, inside of the transverse loops of wall, occupied by corium: in the enlarged section of a loop, in C. balænaris, in Pl. 15, fig. 2 a, the opposed sides are seen to be connected by shelly longitudinal plates. v, cavity occupied by the ovarian tubes and cæca.

PLATE 17.

Genera--PLATYLEPAS, TUBICINELLA, AND XENOBALANUS.

Fig. 1 a, Platylepas bissexlobata, shell of, viewed from the under side; A, rostrum; B, lateral compartment; C, carino-lateral compartment; E, carina. These letters are placed opposite the inward folds of each compartment forming the midribs. 1 b, Platylepas bissexlobata, shell of, viewed externally. 1 c, " " scutum and tergum, viewed externally and separated. 1 d, " " lateral compartment, viewed from the inside, showing the inward folded wall or midrib; a′, ala; d, radius. 2 a, Platylepas decorata, shell, viewed externally; A, rostrum; B, lateral compartment; C, carino-lateral compartment; E, carina. These letters are placed opposite the inward folds of each compartment. 2 b, " " minute portion of external surface of wall, magnified. 3 a, Tubicinella trachealis, natural size; p, tubular soft lip leading into sack; s, scutum; t, tergum. 3 b, Tubicinella trachealis, carino-lateral compartment of a young specimen, natural size; e, broken summit of wall; d, radius: the dotted lines, connecting the two figures, show the size and form which this compartment would have attained, if it could have grown without the summit constantly breaking away. 3 c, Tubicinella trachealis, scutum and tergum viewed from within, and connected by layers of thickened membrane; the scutum is to the left-hand. 4 a, Xenobalanus globicipitis, enlarged; b, skin of the porpoise, with the shell imbedded; at c the lower end of the prosoma of the included animal's body is supposed to be seen through. 4 b, Xenobalanus globicipitis, shell greatly enlarged, seen from above, with the basal membrane at the bottom; the peduncle-formed body having been removed. A, rostrum, on the inner side of this and the adjoining compartments, the transversely ribbed sheath can be seen. B, lateral compartment. C, carino-lateral compartment. E, carina; these compartments are separated by the sutures s s, which run from the top of the shell to the bottom, along the ends of the six rays formed by the adjoining portions of the inwardly folded compartments. a, alæ, of rectangular shape. d, pseudo, or complimentary radii. 4 c, Xenobalanus globicipitis, small portion of external surface of wall of shell, showing the external lamina, a a, which consists only of narrow ledges (expanding and contracting) on each side of the longitudinal septa, c; b, the internal lamina.

PLATE 18.

Genus--CHTHAMALUS.

Fig. 1 a, Chthamalus stellatus, shell, var. a (communis). 1 b, " " " " e (depressus). 1 c, " " " " c (communis). 1 d, " " " " d (fragilis). 1 e, " " scutum and tergum, viewed inside, var. c, British. 1 f, " " scutum and tergum, viewed inside, var. a, Madeira. 1 g, " " scutum and tergum, viewed inside, var. e, Mediterranean. 1 h, " " scutum and tergum, viewed inside, var. c and e, St. Jago, Cape de Verde Arch. 2, Chthamalus antennatus, shell. 3 a, Chthamalus dentatus, shell; 3 b, var. shell, attached to a ship's bottom; 3 c, tergum, viewed from within. 4 a, Chthamalus cirratus, scutum, viewed on inside; 4 b, tergum, viewed on inside. 5 a, Chthamalus Hembeli, shell, old specimen. 5 b, Chthamalus Hembeli, younger shell; C, carino-lateral compartment; a′, ala; d, radius; E, carina; a′, the two alæ. 5 c, Chthamalus Hembeli, scutum, external view of; 5 d, tergum, external view of; e, two of the crests, to which the tergal depressor muscles are attached, much enlarged and viewed from vertically beneath, showing the lateral denticuli or sub-crests. 6 a, Chthamalus fissus, shell; 6 b, scutum and tergum, separated, internal views of.

PLATE 19.

Genera--CHTHAMALUS, CHAMÆSIPHO, AND PACHYLASMA.

Fig. 1 a, Chthamalus intertextus, shell; 1 b, scutum and tergum, calcified together, with the suture obliterated in the upper part, internal view of. 2 a, Chthamalus scabrosus, shell; 2 b, scutum, internal view of; 2 c, tergum, internal view, p, plate forming one side of the cavity in which the depressor muscle is attached; 2 d, tergum, as seen from almost vertically beneath; p, pit for the depressor muscle; q, special pit for the lateral, properly scutal depressor muscle; r, articular furrow. 3 a, Chamæsipho columna, shell; A, rostrum; B, lateral compartment, probably formed by fusion of the rostro-lateral and lateral compartments; E, carina; 3 b, 3 c scutum and tergum, internal views of. 4 a, Chamæsipho scutelliformis, shell much enlarged, seen from above; A, rostrum, separated by imperfect sutures from the (B) lateral compartments, which are formed probably by the fusion of the rostro-lateral and lateral compartments; E, carina; B stands opposite one of the inward folds of the wall, leading into one of the tubular apertures, which runs (generally with an irregular spiral curve) through the whole thickness of the shell down to the surface of attachment. The carina has two of these apertures. 4 b, Chamæsipho scutelliformis, another specimen, seen from the under side, letters of reference the same. 4 c, Chamæsipho scutelliformis, rostrum, disarticulated, enlarged, showing the alæ. 4 d, Chamæsipho scutelliformis, scutum and tergum, internal views of. 5 a, Pachylasma giganteum; 5 b, rostrum of an extremely young specimen, much enlarged, showing its compounded nature, viz., of a true rostrum and rostro-lateral compartments; 5 c, scutum and tergum, external views of; 5 d, scutum and tergum, internal views of.

PLATE 20.

Genera--PACHYLASMA, OCTOMERIS, AND CATOPHRAGMUS.

Fig. 1 a, Pachylasma aurantiacum, shell, lateral view; A, rostrum, separated only by the finest suture from B, the rostro-lateral compartment, which latter has a mere rim-like radius on the side facing the lateral (C) compartment. The latter (C) has a great ala, and is separated from the (D) carino-lateral compartment, by the finest suture; D has a rim-like radius; E, carina, with very large alæ (a). 1 b, Pachylasma aurantiacum, inside view of about half the shell, showing the compound rostrum, consisting of the true rostrum (A) and the two rostro-lateral (B, B) compartments; of the latter, that to the left has a shoulder, receiving the ala of the lateral compartment which has been removed; the ala of the lateral compartment extends, in the upper part, over the whole width of the rostro-lateral compartment, as may be seen on the right-hand, B; C, lateral compartment; D, carino-lateral compartment, with a shoulder (b) to receive the ala of the carina, which has been removed. 1 c, 1 d, Pachylasma aurantiacum, scutum and tergum, external views of. 2 a, Octomeris angulosa, shell seen from above; 2 b, scutum and tergum, internal views of. 3 a, Octomeris brunnea, shell seen from above; 3 b, scutum and tergum, external views of. 4 a, Catophragmus polymerus, shell seen from above. 4 b, " " external view of one of the scales or valves, from the second whorl, counting from the inside. 4 c, " " outline of the basal edges of all the valves of a shell; A, rostrum; B, rostro-lateral; C, lateral; D, carino-lateral compartments; E, carina. 4 d, " " external view of a portion of the shell of a much corroded and worn down specimen, serving almost as a transverse section; C, lateral compartment, D, carino-lateral compartment. 4 e, " " scutum and tergum, internal views of.

PLATE 21.

Genus--VERRUCA.

N.B.--Letters of reference the same throughout the Plate.

A, rostrum. B, carina. S, moveable scutum, S′, scutum fixed and modified so as to form part of the shell. T, moveable tergum, T′, tergum fixed and modified so as to form part of the shell. In S, and S′, a is the occludent margin; b, the basal margin; m, the plate to which the adductor muscle is fixed; o, a ledge formed during continued growth, in the upper part of the fixed scutum, in order to keep the orifice perfectly closed; this ledge is seen distinctly only in fig. 5. In S and S′ the tergal margin is marked by small dashes; (′) being the upper articular ridge, and (′′), the second or lower articular ridge: in S′ (′′) is called the parietal portion of the valve. In T and T′, the scutal margin is marked by small dashes; (′) being the first and upper articular ridge, hardly distinct from the occludent margin, and called in T′′ the occludent rim; (′′) is the second or middle, and (′′′) the lower or third articular ridge, called in T′′ the parietal portion of the valve; x is the carinal margin, called in T′ the carinal rim, and z the basal margin; o is the occludent margin: in T′, a ledge is formed across the under side close to the apex, which ledge is necessary to keep the orifice neatly closed, owing to the apex of the moveable tergum coming to project freely during growth.

Fig. 1 a, Verruca Strömia, specimen with the left hand scutum and tergum fixed and modified into part of the shell. 1 b, Verruca Strömia, (with left hand scutum and tergum fixed), with the valves and compartments separated from each other; the homologous parts of the opercular valves are marked by corresponding letters and dashes. 1 c, Verruca Strömia, left hand scutum and tergum fixed, viewed from the under side. 1 d, Verruca Strömia, smooth var., reversed specimen, i. e., with the right hand scutum and tergum fixed and modified into part of the shell. 1 e, Verruca Strömia, shell seen from the under side; the right hand scutum and tergum (as in 1 d) being the fixed pair: the moveable scutum and tergum (S, T) are seen in the shade at the bottom of the shell, and their shape will be best understood by looking at fig. 1 f. The fixed scutum and tergum S′, T′, differ a little in shape, and in the form of their line of junction, from the same two valves (reversed) in fig. 1 c. 1 f, Verruca Strömia, moveable scutum and tergum, seen from the under side, taken from a specimen, in which (as in 1 d and e) the right hand scutum and tergum were the fixed pair. 2, Verruca Spengleri, scutum seen from the under side, showing the medial, prominent adductor ridge; taken from a specimen, in which the right hand scutum and tergum were fixed. 3 a, Verruca lævigata, scutum and tergum, external view of, from a specimen in which the left hand pair was fixed; 3 b, scutum and tergum, internal view of, from a specimen, in which the right hand pair was fixed. 4, Verruca prisca, scutum and tergum, external view of, from a specimen, in which left hand pair was fixed. 5, Verruca nexa, with the valves separated, the left hand scutum and tergum being the fixed and modified pair. 6, Portion of ribbed shell of a Venus, to which a Verruca Spengleri had been attached, showing the peculiar form of the excavation.

PLATE 22.

ALCIPPE LAMPAS.

Fig. 1, Entire animal (female and two males) greatly magnified, being an unusually symmetrical specimen, partly copied from Mr. Hancock's Plate ('Annal. and Mag. Nat. Hist.' ser. 2, vol. 4, Pl. VIII). H, horny disc and surface of attachment; a, projection formed by the lower end of the lip of the orifice leading into the sack; m, a pair of males, of their proper proportional sizes, attached in their ordinary position. 2, Entire animal, much distorted. 3, Small portion of a Fusus (copied from Mr. Hancock's Plate), perforated by the Alcippe; the darker curved marks are the slit-like orifices, leading into the chambers; the latter are seen from the outside, owing to a difference of tint in the shell of the mollusc where worn thin over the chambers; they are represented by the fan-shaped shaded patches. 4, One of the orifices, leading into a chamber, much enlarged; a, the curved narrow end, which was open and used when the animal was young, but has since been closed externally by sand or shelly matter, and internally by the upward prolongation of the horny disc; b, rims of an inorganic, calcareous deposit, by which the narrow end of the orifice is kept of the due degree of narrowness. 5, Longitudinal section through the outer envelopes of a very symmetrical specimen, giving a lateral view of the included body. a, point at the lower end of the orifice of the capitulum, leading into the sack. b, end of adductor muscle. c, mass of branching ovarian cæca, much developed and protuberant on the under side. d, basal point of the quasi-peduncle, projecting beyond the level of the horny disc (H, H). e, sack or open cavity: of the two branchiæ or ovigerous fræna, one has been removed with the outer envelopes, the other is hidden by the projection caused by the medial distended mass of the ovarian cæca. e′, lateral line of junction of the body to the outer envelopes; which latter have been here cut through in removing the near half of the capitulum and peduncle. f, notch separating the capitulum or upper part from the peduncle or lower part of the external covering: this notch varies much in depth. g, the end (homologically the carinal end), of the orifice leading into the sack, where the cutting of the outer envelopes has commenced. H H, horny disc, cut longitudinally down the middle. h, first pair of cirri. i, prosoma (homologically the second thoracic segment). k, the thoracic segment, which would have borne the second pair of cirri, had such existed. l, thoracic segment, which should have borne the third pair. m, thoracic segment, which should have borne the fourth pair. n, thoracic segment, very small, bearing the fifth pair of cirri. n′, fifth pair of cirri, only one cirrus on the near side being represented. o′, sixth cirrus, borne on the last thoracic segment, too small to be shown. p, caudal appendages. 6, one side or lip of the orifice leading into the sack, greatly enlarged, seen on the inner side, formed of an inner membrane, b, (on which the long hairs and an S-like band of spines, too fine to be plainly represented, are placed), and an outer membrane c, studded with short, thick spines, the corium between these two membranes having been removed; a, projection at lower end of orifice; g, upper end of orifice, showing the point where the corresponding side or lip of the orifice has been cut away. 7, small portion of the external membrane, showing the star-shaped, hard, projecting points of chitine; but they are here placed too closely together. 8, front view of mouth, greatly enlarged, and with the gnathites rather unnaturally separated from each other; h, the first pair of cirri; in front, the outer maxillæ appear like a bilobed lower lip; the inner maxillæ (with their singular membranous swelling behind, see fig. 15), can be distinguished by their long apodemes or horny imbedded bars; behind are seen the one-toothed mandibles, with a swelling behind, probably representing the palpi; all above the mandibles consists of the immensely developed labrum, with the foreshortened ends of the row of long hairs on each side; the fold, or articulation, separating the mouth and body, is seen crossing above the basal ends of the apodemes of the maxillæ. 9, Lateral view of the coriaceous button or cushion, c′, on one corner of the upper segment, b, of the pedicel of the sixth cirrus; c, being the lower part of the lower segment of the one ramus of this same cirrus: the hooked hairs are rather distorted. 10, The same, viewed from the inner side. 11, Lateral view of the labrum, with the mandible, m, attached to it, which latter, from overhanging the œsophagus, shows the position of the mouth; h h, is the first cirrus on the near side; b, is the medial crest of labrum, on the side of which extends a long row of hairs; a a a, delicate membrane of side of body, attached to the margins of the labrum. 12, Diagram showing the probable manner in which the young Alcippe bores into the shell of molluscs; a, pupa attached by the antennæ to the outer surface of shell; b, outline of young Alcippe soon after its metamorphosis; the anterior or lower end has increased considerably in length, so as to project beyond the point whence the antennæ rise, and it has now penetrated the shell, being attached to the roof of its incipient chamber by its horny disc, represented by a thick black line; c, is the Alcippe after further growth, when it has succeeded in burying itself; the horny disc is now attached parallel to the surface of the shell; the horny disc of its former state, now lines the narrow end of the slit-like orifice leading into the shelly chamber: the above changes in position are supposed to have been effected quite gradually. The diagram, c, I may add, represents the position of the Alcippe for the rest of its life, the chamber being added to at both ends, sides, and bottom. 13, Lateral view of the posterior extremity of the thorax, much enlarged, with its articulated appendages represented only on one side; the four thoracic segments, l, m, n, o, correspond with those represented in fig. 5. In one monstrous specimen, segment n, bore a single cirrus. The posterior thoracic segment, o, bearing the sixth pair of cirri, o′, is very small and obscure, and can be seen only by separating the fifth and sixth pairs of cirri; or by longitudinally bisecting the thorax, and viewing the inner side; n′, fifth cirrus; a, lower segment, b, upper segment of pedicel; c, lower, and d, upper segment of the one ramus, the other ramus being represented by the coriaceous boss c′; o′, sixth cirrus, with similar segments; p, caudal appendage. 14, First cirrus. 15, Maxillæ, with the lower end of the apodeme cut off, showing the curious membranous swelling on the side towards the mandible.

PLATE 23.

Genera--ALCIPPE AND CRYPTOPHIALUS.

ALCIPPE LAMPAS.

Fig. 16, Pupa of male Alcippe lampas, viewed laterally; a, antennæ, c′, eyes attached to the apodemes; above these the single eye of the mature male may be distinguished. 17, Abdomen of the same; p, posterior end of thorax; q, abdomen; r, caudal appendages. 18, Male of Alcippe lampas immediately after the metamorphosis, the ventral surface being uppermost, but the specimen has been in some way distorted, as the lobe (i) ought to project on the opposite side; a, antennæ of the pupa; g, h, lateral lobes; internal organs not yet formed; orifice at upper end (i) not visible; scale same as for the pupa, fig. 16. 19, Male of Alcippe lampas, when fully mature; scale same as in last figure (18) and as in fig. 16. a, antennæ of pupa. b, vesicula seminalis. c, eye, (seen in fig. 16 above the eyes of the pupa, c′.) d, testis. e, lower transverse muscle. f, upper transverse muscle. g, h, lateral lobes of the external covering, answering to the sides of the peduncle of the female. i, terminal lobe on the ventral side of the orifice, probably corresponding with a in fig. 1, Pl. 22. k, orifice of the tubular sack. l, oblique muscles on the ventral side of the sack. m, probosciformed penis, shown exserted; m′ portion within the tubular sack.

CRYPTOPHIALUS MINUTUS.

Fig. 1, Cryptophialus minutus (female with an attached male) viewed laterally, but with the disc (H) rather turned towards the beholder, much enlarged; a, orifice leading into the sack; H, thin horny disc by which the animal is attached within its cavity; H′, upper free worn edge of the disc; z, male attached in its usual position to the edge of the disc of the female. 2, Cryptophialus minutus, natural size, within a half-inch circle; this represents the largest specimen which I have ever seen. 3, Half the orifice, with a large portion of the external membrane and of the membrane lining the sack. a, a, dentated horny rim of orifice. b, b, external membrane, with the underlying corium or true skin removed. b′, a horny bar, expanding at its lower end into a toothed plate, and at the upper end connected with the horny rim round the orifice. c, c, membrane lining the sack. c′, horny bar by which this membrane is strengthened. c′′, thickened membrane, or bar, expanding into fibrous sheets for the attachment of a muscle. d, delicate lateral lip, within the outer dentated horny rim. 4, Orifice of sack, cut off, widely open, viewed from above; a, horny dentated rim; b′, top of horny bar, where united to the rim; d, inner lateral lip folded backward; d′, lip, with coarser hairs, at the carinal end of the orifice. 5, Animal with the outer tunics removed, viewed laterally. a, dentated horny rim of orifice, continuous with b, outer membrane, here cut off. c, inner membrane of sack, continuous with c, c, the reflexed membrane of the body, by which the body is united to the disc and outer envelopes. e, lancet-shaped labrum. e′, projection behind the labrum. f, palpi. g, outer maxillæ, between which and the palpi lie the inner maxillæ and mandibles; these latter are rather exaggerated in size. h, first maxilliped, in a rudimentary condition, close above which is the articulation separating the whole mouth (o) from the first (^1) segment of the body. i, k, tapering appendages springing from the second and third segments of the body. l, pedicels of the three pairs of abdominal cirri. m, cirri, three pairs of. o, mouth, of great size, formed by the confluence of the lower segments of the gnathites. ^1, first segment of body, homologically the last or seventh cephalic segment. ^2, second segment of body, homologically the first thoracic segment. ^3, third segment of body, homologically the second thoracic segment. ^4, fourth segment of body, homologically the third thoracic segment. ^5, fifth segment of body, homologically the fourth thoracic segment. ^6, sixth segment of body, homologically the fifth thoracic segment. ^7, seventh segment of body, homologically the sixth thoracic segment. ^8, eighth segment of the body, homologically the seventh thoracic segment. 6, Front of mouth; g, outer maxillæ; g′, an articulation separating the mouth from the membrane of the first segment of the body; h, first pair of maxillipeds; whole figure on same scale with the labrum, fig. 9. 7, Maxillæ, drawn on thrice the scale as the outer maxillæ; a, apodeme. 8, Mandibles, drawn on thrice the scale as the outer maxillæ. 9, Labrum, on same scale with the outer maxillæ, fig. 6, and one third of the scale of the mandibles and inner maxillæ; e, labrum; f, palpi.

PLATE 24.

Genera--CRYPTOPHIALUS AND PROTEOLEPAS.

CRYPTOPHIALUS MINUTUS.

Fig. 10, Lower enlarged end of œsophagus, where entering the stomach, viewed from one of the sides bearing the discs of teeth; a, upper cut off end of œsophagus; b, the lower end and natural opening; c, thickened rim, having a somewhat beaded structure. 11, The same; diagram giving a transverse section of the above in the line of the discs of teeth; c c c c, four thickened beaded edges; e e, two other but narrower and less prominent beaded edges; d d, discs of teeth; f, rows of fine bristles; the almost double row of bristles on each side under (d) is not of course seen in this section. 12, Lower end of œsophagus viewed from a position at right angles to that in fig. 10; or from the side e, of the diagram, fig. 11; the two discs of teeth are consequently shown in profile; a, upper cut off end of œsophagus; b, lower natural end; c, c, thickened edges; e, narrower thickened edge, projecting towards the beholder; d, disc of teeth seen in profile. 13, Portion of one of the cirri; a, lower segment of pedicel; b, upper segment, supporting the two rami. 14, Segments of one of the rami much enlarged; a, thickened shield-like portion of membrane. 15, Ovum, (thirty-five times the natural size.) 16, Egg-like larva in the first stage, on same scale. 17, " " in the second stage, on same scale. 18, Larva in the last or pupal stage, on four times the scale of fig. 15-17; a, antennæ; b, apodeme and eyes; c, abdominal bristles. A male would have been developed from this pupa. 19, Male on same scale as the pupa, fig. 18; a, three terminal segments of the antennæ of the pupa; d, orifice of the sack.

PROTEOLEPAS BIVINCTA.

Fig. 1, Antenna of the pupa (three terminal segments of), with a portion of one of the two threads, enclosing the cement-ducts, by which the body of the Proteolepas is attached; the upper portion of the thread, and the adjoining part of the body, are represented in section. a, part of the great mass of cellular matter within the ovarian sack, in process of development into ova, and changing its character as soon as it enters the tube or cement-duct. b, membrane forming the ovarian sack and the cement-ducts, the latter enclosed within the threads of attachment. c, corium lining the outer membrane of the body, and the upper part of the threads. d, outer membrane of body. e, " " becoming suddenly thicker where forming the outer membrane of the thread. e′, outer membrane of the thread in the lower part, here not shown in section. f, main or second segment of the pupal antenna, the basal segment having, as in all cases, been moulted, with the carapace of the pupa. g, disc-segment, apparently with a small orifice for the issuing of the cement. h, terminal segment with the shorter spines broken off. 2, Compounded mandibular organ, sketched by the camera; a, supposed mandible; b, perhaps portion of the mandible; c, maxilla; d, ligamentous fibres giving attachment to muscles. 3, Mouth seen from the ventral side, sketched by the camera; r, articulation separating the mouth from the body; c, compounded mandibular organ; d, palpus, united to the opposite palpus and to the crest of the labrum; the latter forming the back of the hollow in which the compound mandibles work. 4, Diagram of the mouth of an ordinary cirripede, seen from above; a, outer maxilla; b, maxilla; c, mandible; d, labrum. 5, Diagram, illustrating the supposed changes in position of the gnathites in Proteolepas, causing them to stand back to back; a, outer maxilla; b, maxilla; c, mandibles; d, labrum.

PLATE 25.

Genera--PROTEOLEPAS AND BALANUS.

PROTEOLEPAS BIVINCTA.

Fig. 6, Proteolepas bivincta: diagram, showing the probable position of the young animal, just before its metamorphosis, within the carapace of the supposed pupa; a, caudal appendages; b, six pairs of natatory thoracic legs; c, mouth, no doubt closed and functionless, as in other pupæ; g, threads of attachment, with cement-ducts in process of formation; h, antennæ. 7, Proteolepas bivincta, magnified about twenty-six times. m, mouth, the summit being formed of the labrum and palpi joined. ^{1}c, first segment of body; homologically the seventh or last cephalic segment. ^{2}t to ^{8}t, second to eighth segment of body; homologically, first to seventh thoracic segments. ^{9}a to ^{11}a, ninth to eleventh segment of body; homologically, three segments of abdomen. d′, three muscles attached on each side to the labrum, and running to the gnathites. e e, great ovarian sack. f, true ovaria. g, threads of attachment. h, three terminal segments of the antennæ of the pupa. i, vesicula seminalis. k, papilla representing the penis.

Fig. 1, Balanus tintinnabulum: an enlarged longitudinal section through the shell and sack, with the right-hand scutum and tergum and right-hand half of shell and basis removed, exhibiting the body of the animal not in section. The cirri are exhibited only on one side. A, A, orifice of shell, within which lies the operculum formed by a pair of scuta (S), and pair of terga (T). B, basis (homologically the anterior end of the shell). K, carina of shell (or dorsal valve or compartment of shell). K′, sheath of carina. L, lateral compartment of shell. The carino-lateral compartment is hidden by the scutum and tergum. R, rostrum of shell (or ventral valve or compartment of shell). R′, sheath of rostrum. O, O, opercular membrane, connecting the opercular valves with the overhanging basal edge of the sheath. S, scutum. T, tergum. a, adductor scutorum muscle, with the scutum on the near side removed. b, the whole space enclosed by a broken sinuous line, round a and b, shows the cut surface of attachment to the near scutum, which has been removed. b′, lower muscle, on the near side, running from near the basal edge of the scutum to near the basal margin of the labrum (e). Above this are three other muscles (all on the near side), running to the membrane between the labrum and adductor muscle. c, prosoma, including the main portion of the stomach and thickened ends of the vesiculæ seminales: homologically this is formed by the development of the second thoracic segment, which carries the first pair of cirri; and possibly, in part, by the antecedent segment, i. e. the first thoracic segment. c′, thorax, extending from the prosoma to the posterior end of the body: the letter (c′) stands on the segment supporting the third cirrus; homologically, this segment is the fourth thoracic. d′, orifice of the acoustic sack, above which is the basal articulation of the first cirrus. e, labrum, forming the back (i. e. anterior end) of the mouth, with the transverse palpi obscurely seen on the summit. f, sack in which the animal lies, with the tunic lining it, continuous with that investing the prosoma (c), and lining the under sides of both opercular valves, but cut off round (b) and (a) by the removal of the near scutum. The branchia on the further side, which occupies the position represented at fig. 3, is covered by the body of the animal. g g, ovarian, inosculating cæca, branching from the simple duct (of which the near one of the pair is represented), leading to the ovaria (not represented) within the body. h, rostral depressor muscle of the scutum: the lateral depressor muscle of the scutum is hidden by the body and by the membranes of the sack. i, carinal depressor muscle of the tergum. z, antennæ (three terminal segments) of the pupa; I distinctly saw these in this species, but they are here represented considerably too large, even on the supposition that a young shell had been drawn, and magnified about twelve times. 2, Testes of Balanus perforatus, greatly magnified. 3, Branchia of Bal. tintinnabulum, on the same scale as in fig. 1, and in its natural position. This drawing was made by lifting up the body in fig. 1; the organ being thus completely exposed over its whole interior surface; a is the basal end of the spur of the tergum.

PLATE 26.

STRUCTURE OF THE MOUTH AND THORAX.

N.B.--The same letters of reference are used for the parts of the mouth throughout this plate. All the organs here represented have been cleaned by boiling in potash, and consist exclusively of the external membrane.

Fig. 1, Mouth of Balanus perforatus, viewed from vertically above, with the first pair of cirri x x in their proper position, cut off close above their basal articulations. a, outer maxilla; a′, ditto, cut closely off. b, maxilla. c, mandibles. d, palpus; d′ ditto, cut closely off. e, labrum, crest of. x x, first pair of cirri, cut off. 2, Supra-œsophageal cavity of the mouth of Balanus improvisus, torn open, with the palpi, mandibles, and maxillæ removed, exhibiting the inner face of the labrum, laid flat, and the inner faces of the outer maxillæ; scale as in fig. 1. a, outer maxillæ; a′′, inner and lower lobe of ditto. d′, point of attachment to the torn-off palpus. e, labrum, crest off; e′, central notch, with graduated teeth on both sides. f, triangular thickened portion of the inner fold of the labrum; f′, rib or bar of membrane, thickened to support the surrounding very thin membrane of the supra-œsophageal cavity. g, opening of the œsophagus. h, forked bar of thickened membrane, for same purpose as f′. 3, Mouth of Coronula balænaris, divided vertically in a transverse line, with the outer and inner maxillæ and mandible on the left side removed, with the labrum, the other mandible and both palpi viewed on the inside, and with the œsophagus adherent in its proper position. c, Mandible, upper free segment; c^1, second or middle segment; c^2, supposed third or basal segment, forming the basal margin of the mouth, but not separated by any articulation from the labrum. d d, palpi; d′, aperture, through which the inside of this palpus can be seen, caused by the mandible having been cut off; the membrane on the under side of this aperture is thickened, and affords the chief support to the palpus; d′′, thin membrane, apparently part of the palpus, connecting the attached basal end of the palpus to the externo-lateral surface of the mandible. e′, central notch in the crest of the labrum; e′′ e′′, basal margin of the labrum, to which the membrane of the body is joined. f, thickened portion of membrane, part of the inner fold of the labrum, corresponding with f in fig. 2. g, orifice of the œsophagus, with the front part of the supra-œsophageal cavity cut away; g′, lower, expanded, or bell-shaped, end of the œsophagus, in its natural condition. i, k, concavities for the attachment of muscles running to the mandibles. m, cut off edge of membrane forming the side of the mouth, which cut edge can be followed up above the aperture d′, where the upper basal end of the palpus has been cut off, and so onwards by g, to the mandible on the opposite side of the mouth. 4, Mouth of Coronula balænaris, viewed from the outside, in front, with the inner maxilla, mandible, and palpus on the left side of the figure, and nearly the whole labrum, and the greater part of the palpus on the right side, all cut away. The maxilla, mandible, and basal portion of the palpus on the right hand, are pulled out of their proper positions; for the toothed edge of the mandible ought to have stood higher, and nearly in a line between and behind the outer maxillæ, and then the basal margin e′′ of the lateral portion of the labrum would be raised, and curling round, would stand nearly where the letter b′ is now placed. a a, outer maxilla, upper free lobe; a′′, lower and inner free lobe; a^1, supposed second or middle segment; a^2, supposed third or basal segment; a′′′, basal articulation of mouth, separating it from the ventral surface of the thorax. b, inner maxilla; b′, apodeme of do. c, mandible, upper free segment; c^1, second segment; c^2, third and basal segment, but not separated by an articulation from the labrum. d, palpus; d′′, membrane uniting the basal end of the palpus, where attached to the labrum, to the side of the mandible. e′′, basal margin of the labrum, on one side, displaced and pulled down. n, orifice of the olfactory pouch. 5, Balanus amaryllis: mandible, upper free segment, seen from the side that faces the labrum; p, an arched line, where the thickened membrane of the upper free part terminates, and is united by thin membrane to the near side of the palpus; q, ligamentous bands for the attachment of muscles. 6, Balanus amaryllis: palpus, on the same scale as the mandible, fig. 5, seen from the outside, so that the further or under face is the side which, towards the right hand, is united to the near face of the mandible, fig. 5; r, long bristles, springing from a protuberance near the extremity; these bristles, in many species, form a long single row, parallel to the basal margin; s, upper row of shorter bristles; t, row of very short bristles, arising from the further side and curling over the crest of the labrum. 7, Balanus amaryllis: maxilla on twice the scale of the mandible and palpus; b, upper free segment; b′, apodeme; b^1, thickened portion of membrane, perhaps answering to the second segment of the mandibles; b^2, thin membrane, extending down to the basal edge of the mouth, possibly answering to the basal segment of the mandibles; or perhaps the thickened membrane forming the protuberance c^2 in fig. 3, may be considered as the basal segment of the maxillæ. u, step-formed projection at lower angle of maxilla. 8, Thorax of Coronula diadema: outer membrane of the five posterior segments laid almost flat, and viewed externally as a transparent object. ^2 to ^6, the second to the sixth cirrus, cut off a little above their basal articulations. a, basal curved end of the probosciformed penis. b, anus; b′, the membrane surrounding the anus, probably consisting of a rudiment of the abdomen. c, rectum, seen through on the under side. d, basal articulation of the sixth cirrus; d′, do. of the fifth cirrus; d^2, do. of the second cirrus. e e′, posterior thoracic segment, carrying the sixth pair of cirri; the dorso-lateral portion e is separated, in this one segment, from the corresponding portion e′ by a narrow slip of thinner membrane, which may be a part of the abdomen let in. e^2 e^2, thoracic segment, supporting the second pair of cirri. f, f^3, folds or articulations between the adjoining segments. g, swollen, punctured portions of membrane, not differing homologically from the rest of the segments. h, posterior portion of the prosoma, or the specially enlarged part of the thorax; it carries the first pair of cirri; homologically h forms part of the second segment of the thorax of the archetype Crustacean.

PLATE 27.

NERVOUS SYSTEM AND SENSES.

Fig. 1, Nervous system of Coronula diadema, seen from the ventral surface. A, infra-œsophageal ganglion; two pairs of rather small nerves, arising from the dorsal surface, cannot be here shown. B, supra-œsophageal ganglion, double. C, ophthalmic ganglion, single. D D, eyes, as believed to exist. a, three pairs of nerves, running to the gnathites and olfactory pouches; a′, nerve rising from the collar, running towards the mandibles. b, single medial nerve, running to the great transverse muscle, extending across the upper part of the stomach. c, collar-nerve or chord, uniting the infra- and supra-œsophageal ganglions. d, great splanchnic nerve, here spread laterally out, but properly running along the sides of the upper part of the prosoma, and therefore under the collar-nerve; d′, plexus by which this nerve is connected with the supra-splanchnic nerve, e. e, supra-splanchnic nerve, rising from the collar, almost in contact with the supra-œsophageal ganglion; e′, small nerve rising from the end of the supra-œsophageal ganglion, and running to the adductor and surrounding muscles. f, f, pair of great nerves (antennular), distributed over the sack and shell. g, chord (in appearance single), uniting the supra-œsophageal ganglion with the first (C), or ophthalmic ganglion. h, small medial nerve, running to near the adductor muscle. i, nerve supposed to run from the ophthalmic ganglion to the eye. k, small nerve, rising from the main ganglion (A), between r^1 and r^2, or the nerves running to the first and second pairs of cirri. œ, position of the œsophagus. r^1 nerve entering the first cirrus. r^2, r^3, r^4, r^5, r^6, nerves entering the five succeeding pairs of cirri. s, nerve entering the probosciformed penis. 2, nervous system of Balanus tintinnabulum; letters of reference as in fig. 1. 3, acoustic sack of Balanus tintinnabulum. 4, " " Coronula diadema. 5, eye of Balanus tintinnabulum; i, nerve coming from the ophthalmic ganglion; D, eye itself.

PLATE 28.

CEMENTING APPARATUS.

Fig. 1 a, Basal membrane, with the cementing apparatus, of Coronula balænaris; a small portion of the parietal membrane, p p p, which coats the folded shelly walls, is left adherent to the basal membrane. b, the circumferential slip (shaded more darkly than the rest to catch the eye), separating the basal from the parietal membrane. c′ c′, slips of basal membrane, formed at each period of growth, and overlapping each other. s s s s s s, the six sutures in the walls, separating the six compartments, of which-- A is the basal margin of the rostrum, C C that of the lateral compartments, D D that of the carino-lateral compartments, and E that of the carina. r, r, rays or spokes of membrane, prolonged from the circumferential slip, and running under the trebly folded wall of each compartment, but here cut off; a similar ray should run under each line of suture (s). These rays, at their extremities, expand transversely; and the shape and length of the rays may be judged of from the basal outline of the folded walls given in Pl. 16, fig. 5. The two cement-ducts, proceeding from each cement-gland, debouch opposite the middle folds of the lateral (C C) and carino-lateral (D D) compartments. The layers of cement have been removed. N.B. There is one considerable error in this figure, the two main trunks, connecting the cement-glands, and meeting at the centre, have been represented as forming a straight line, but in fact they form a very open angle, as is correctly shown in fig. 1 c. 1 b, Diagram, representing a vertical section through a portion of the basal and parietal membranes, with the thickness of the membrane enormously exaggerated. z z z, layers of cement, which, if the section had been made in the line of the cement-ducts, would have been seen proceeding out of these ducts, as is represented at (t), where the section is supposed to have taken the above course. c′ c′, the slips of basal membrane. b, the circumferential slip; beneath this the coarsely dotted layer represents the cement, lately excreted, and before it has acquired its proper transparent structureless character, elsewhere represented by fine dots. p, membrane externally coating the walls of the shell. t, cement-ducts opening beneath the basal membrane. 1 c, The central portion of fig. 1 a, considerably magnified. c′ c′, slips of the basal membrane; but the shell, when these were formed, was so young that the walls had not acquired their folded structure; in the centre the prehensile antennæ of the pupa may be obscurely seen. f, the main cement-trunk, connecting the cement-glands. h, a cement-gland, from which two cement-ducts proceed. a a, cement-ducts (cut off), leading to opposite the middle fold of the carino-lateral compartment. b b, cement-ducts (cut off), leading to opposite the middle fold of the lateral compartment. a′ b′, a pair of cement-ducts, with their orifices opening on the under side of one of the slips of basal membrane (c′), at a point which once was opposite the middle of the carino-lateral and lateral compartments. The orifices of the other ducts, towards the centre, may be seen forming straight lines. 2, Cement-ducts and one cement-gland of Chelonobia patula, represented without the basal membrane, to which they adhere: f, f, main cement-trunk; g, enlarged portion; h, gland; a, b, the two ducts proceeding from this gland, and bifurcating several times before debouching on the under side of the basal membrane. Several other cement-ducts, proceeding from other glands, are represented just as they appeared under the microscope. 3, Cement-ducts and glands of Tubicinella trachealis, represented without the basal membrane to which they adhered: (f) (f), main cement-trunk, connecting the several glands; h, cement-gland; a, cement-duct, with a singular loop (a′) having two projections or rudimentary branches; b, spur or rudiment of a second cement-duct; c, third cement-duct. 4 a, Chain of cement-glands of Balanus tintinnabulum, with all the ducts removed, excepting those proceeding from the last formed gland, which latter correspond in age with the last-formed zone of the shelly basis; the whole of the basis having been removed by acid. f, main cement-trunk connecting the glands. gh, last-formed cement-gland. k, t, two cement-ducts, proceeding from a great common duct; one of these bifurcates at (t), and one branch joins at (t′) the corresponding branch from the corresponding gland. i i i, circumferential duct, into which the ducts k, k, t, t, t′ all enter. i′ i′, branches proceeding from the circumferential duct, which branch and sub-branch till they form a sheet (z z) of cement-tissue on the outside of the basis of the shell. 4 b, two cement-glands of Bal. tintinnabulum (this figure, to match with 4 a, ought to have stood upside down), taken from near the centre of the basis, greatly enlarged; (f f), main trunk; (g), enlarged portion of the trunk; (h), gland; k, t, two cement-ducts proceeding from a common point, one of them (t) bifurcates, and gives off a rudimentary branch, t′; m, a spur, or rudimentary duct. The gland, h, has been pushed on one side, it ought to lie over the enlarged portion (g). There is a considerable difference between these two glands and that (gh) represented in fig. 4 a; the neck of the gland in the latter being elongated into a great common duct, and the spur or rudimentary duct (m) being absent.

PLATE 29.

CIRRI AND LARVÆ, FIRST STAGES.

Fig. 1, Sixth cirrus of Balanus amphitrite (var. cirratus), showing the muscles. a, b, flexor and extensor muscles, moving the upper segment (i to k) of the pedicel. c and d, flexor and extensor muscles, apparently moving the lower segments of both rami, as a whole; the lower articulations in these rami being confluent. e and f, flexor and extensor muscles extending up both rami (those only in the near ramus being figured) to their tips. g g, flexors of the separate segments in both rami. h, basal articulation of lower segment of the pedicel. i, upper articulation of lower segment of the pedicel. k, upper articulation of upper segment of pedicel. 2, Fourth cirrus of Acasta sulcata. i, upper articulation of the lower } _These two letters segment of pedicel. } apply to all the k, upper articulation of the upper } figures 1 to 6._ segment of pedicel. } l, curved teeth on the pedicel. m, " " on the segments of the anterior ramus. 3, Third cirrus of Chthamalus antennatus. 4, Second cirrus of Balanus perforatus, viewed exteriorly and laterally. 5, Third cirrus of Xenobalanus globicipitis. 6, Sixth " " " 7, Spermatozoa (copied from Mr. C. Spence Bate, in 'Annals and Mag. of Natural History' (S. 2), vol. viii, Pl. VIII). a, of Verruca Strömia, in an early condition. b, of Balanus balanoides, more mature. c, of Balanus perforatus, apparently mature. 8, Larva of Scalpellum vulgare, immediately after coming out of the egg, seen on the ventral surface (letters of reference given below). 9, Larva of Balanus balanoides, immediately after coming out of the egg, seen on the ventral surface, copied from Mr. C. Spence Bate's drawing in 'Annals and Magazine of Natural History' (S. 2), vol. viii, Plate VI, fig. 1 (letters of reference given below). 10, Larva of Chthamalus stellatus, after the first moult, but during the first stage, seen on the ventral surface, copied; with some alterations, from Mr. C. Spence Bate's drawing in 'Annals and Magazine of Natural History' (2 Ser.), vol. viii, Plate VIII, fig. 13.

(The following letters apply to above figs. 8, 9, 10.) a, eye. b, first pair of antennæ, not observed in fig. 9. b′, the same antennæ, as yet encased (in fig. 8) within small horns. c, horns, including the second pair of antennæ. d, mouth, probosciformed: in fig. 8, the specimen having been acted on by potash, the œsophagus can be seen within, with the orifice beneath the swelling, which latter perhaps answers to the labrum. e, first, uniramous natatory leg (homologically the second thoracic limb). f g, second and third, biramous natatory legs (homologically the third and fourth thoracic limbs.) h, posterior point of carapace. i, forked terminal projection of the body or abdomen. l, second forked projection. m, two sharp points, apparently representing a third forked projection. n, a rounded swelling, apparently lying between the carapace and the supposed abdomen, and believed to form the anus.

PLATE 30.

LARVÆ OF LEPAS: SECOND AND LAST STAGES OF DEVELOPMENT.

Fig. 1, Larva of Lepas in the second stage of development; a, supposed antennæ (second pair); m, mouth; c, three pairs of legs. (Copied from Burmeister's 'Naturgeschichte der Rankenfüsser,' Tab. 1, fig. 3.) 2, Lepas australis: pupa or larva (2 a, of natural size) in the last stage of development, with the young cirripede in its natural position, obscurely seen within,--the specimen having been treated with caustic potash, and so rendered transparent,--viewed laterally and greatly enlarged. Scarcely more than the outline of the shell or carapace is represented. The darkly shaded part to the left represents the extent of the sack of the pupa, or the cavity occupied by the thorax, with its limbs. a, both antennæ, adhering by their discs to a piece of wood. b, dorsal surface of the shell or carapace; and immediately underneath this letter is the point of reflection of the membrane investing the thorax, so as to line the sack of the pupa. b′, is the posterior end of the animal, and of the orifice on the ventral surface, through which the legs are protruded. c, six pairs of natatory legs. d, pair of caudal appendages, seated on a minute abdomen. m, mouth, from which the œsophagus can be seen running into the stomach, the latter having two dark cæca; the stomach sweeps round in the pupa to the abdomen, near b′; but in the young included cirripede, only as far as the letter (b), where the bases of the posterior pair of cirri and the anus lie. n, apodemes, supporting the eyes, produced deeply inwards from the eye-bearing segment (N, in fig. 4) of the antennæ. s, bottom of sack of the young cirripede immediately after its metamorphosis; it extends as far as s′. (See s, in fig. 3.) t, gut-formed cement-gland (or incipient ovaria), seen on the near side of the animal, whence a cement-duct, t′, runs into the near antenna. u, internal and anterior part of the pupa, filled with pulpy, oily matter, together with the incipient muscles of the peduncle; when stretched out it forms the peduncle of the young cirripede. See u′, in fig. 3. x, bases of the pedicels of the cirri of the young included cirripede. 2 a, Pupa of Lepas australis of natural average size, within a half-inch wide. 3, Young cirripede (on a smaller scale than Fig. 2), immediately after the exuviation of the bivalve-like pupal carapace, the basal segments of the antennæ, the eye-apodemes and eyes. The young cirripede has just assumed its proper position at nearly right angles to what it held whilst packed within the pupa,--this change of position having been effected by the opening out or stretching of the deep fold of membrane (see n, in fig. 2) formed over the eye-apodemes and eyes, previous to the act of exuviation. a, the three terminal segments of the antennæ of the pupa, still remaining cemented, in the same position as before, to the same piece of wood: the basal, or eye-bearing segment (N, in fig. 4), has been moulted with the pupal carapace. c, d, legs and caudal appendages of the pupa, not as yet moulted, but quite functionless; the external membrane of the thorax, and that lining the sack of the pupa, are, likewise, as yet retained, but soon will be cast off. s, bottom of the sack of the young cirripede, which can now be easily distinguished. u′, the peduncle. x, y, z, primordial valves, composed of chitine: x, being the scutum; y, the tergum; z, the carina. 3 a, small portion of one of the primordial, non-calcified valves, much magnified. 4, ventral surface of pupa; on the same scale, and in the same semi-transparent condition as in fig. 2. a, antennæ. b, limit of sack on the sides in the ventral or lower half of the pupa. b′, posterior end of the carapace. c, d, bristles of the natatory legs and of the caudal appendages, protruded through the orifice of the carapace. e, orifice of the acoustic sacks. m, mouth, with the œsophagus attached to it, obscurely seen through the carapace; the stomach having been removed. n, apodemes supporting the eyes. N, the eye-bearing or basal segments of the antennæ. o, the second or main segment of the antennæ. p, the third or disc segment of the antennæ. v, the fourth or terminal segment of the antennæ. W, ventral surface, bordered by the edges of the carapace; the letter stands near the extremity of the œsophagus. 5, First pair of natatory legs: f, lower segment of pedicel; g, upper segment of pedicel; h, lower segment of ramus; i, upper segment of ramus; k, outer ramus; l, inner ramus of same leg; r, sternal surface between the first and second pairs of legs, with singular thickened ridges and folds. 6, Abdomen with two caudal appendages: ^1, first abdominal segment, attached to the posterior thoracic segment; ^2, second abdominal segment; ^3, third or last abdominal segment; h, lower segment; i, upper segment of caudal appendage. 7, Transverse section of the pupa, close to the eye-apodemes; these being made to stand more upright than in fig. 2. The internal organs of the animal have all been removed. a a a′, section of carapace; from a to a′, on the lower side, forms the ventral surface, with three longitudinal furrows, here in some degree opened out. c, crest of thick membrane on each side, forming the sides of the lateral furrows. N, the posterior margin of the eye-bearing segment (see fig. 4) of the antennæ; the edges of which are hardened and thickened, and are produced inwards, forming n, the apodemes, to which are attached the (n′) great compound eyes. 8, Terminal portion of an antenna, greatly magnified, seen from above. o, part of the second or main segment; an oblique line shows a line of separation of the upper thinner and lower thicker membrane; o′, single spine borne at this segment. p, disc-segment, bearing seven spines; p′, an irregular border of the cement-tissue, believed to have debouched through the spoke-like minute tubes seen on the disc. v, terminal segment, projecting almost rectangularly outwards; v′, most delicate tube or ribbon, believed to consist of cement-tissue.

ERRATA.

Page

104, thirteen lines from bottom, for "Balanus elongatus," read "Balanus galeatus."

105, six lines from bottom, for "Balanus elongatus," read "Balanus galeatus."

174, Since the table on the distribution of the fossil species was drawn up, I have examined some more specimens, sent me by Mr. Wood, which show that Balanus concavus and Hameri are found in the Red Crag; and that Verruca Strömia is found in the Coralline Crag; this will make the total in the Coralline Crag ten, and in the Red Crag eight. I should, however, add, that the identification of Verruca Strömia in the two Crags is a little doubtful, as the specimen was without the opercular valves.

235, to Fossil localities of Bal. concavus, add Red Crag (Sutton) Mus. S. Wood.

255, six lines from the top, Bal. crenatus, I have now seen a single Red Crag specimen .5 of inch in basal diameter.

278, to Fossil localities of Bal. Hameri, add Red Crag (Sutton) Mus. S. Wood.

293, nineteen lines from the top, for "Cotantin," read "Cotentin."

300, ten lines from bottom, for "parieted" read "parietal."

INDEX.

N.B. The names in italics are synonyms or doubtful species.

Abdomen of the Balanidæ, 65. of larvæ in first stage, 108. in pupa of Alcippe, 548.

Abdominalia, order of, 21, 563.

Acasta, sub-genus, 302. cyathus, 312. fenestrata, 316. glans, 314. lævigata, 315. Montagui, 308, 492. purpurata, 318. spinulosa, 321. spongites, 308. sporillus, 319. sulcata, 310. tubulosa, 320. undulata, 313.

Acorn shell, 33.

Adductor scutorum, 53.

Adna, genus, 354. Anglica, 360.

Affinities of the Balanidæ, 152.

Alæ, structure of, 37, 47.

Alcippe, genus, 529. lampas (female), 530. lampas (male), 555. sexes of, 23.

Anelasma, false, resemblance to Xenobalanus, 445. compared with Alcippe, 528.

Antennæ of larva in first stage, 105. of pupa, 114. of Alcippe, 549. of Cryptophialus, 581. of Proteolepas, 601.

Anus, 87. none in Proteolepas, 596. none in the male Alcippe and Cryptophialus, 546, 562, 585.

Apoda, order of, 22, 587.

Apodemes for the attachment of eyes of pupa, 120, 126.

Apparatus, cementing, 133.

Appendages, caudal, 65, 85, 479, 481, 491. in Verruca, 510. in Alcippe, 543. filamentary, to sack, 64. to limbs, 64, 83.

Asemus, genus, 321. porosus, 329.

Astrolepas, genus, 382. lævis, 396. rotundarius, 392.

Attachment of Chelonobia to turtles, 390. of Coronula to whale's skin, 411. of Tubicinella, 436.

Baer, Von, on morphological differentiation, 19.

Balanidæ, family of, 33. highest Cirripedes, 20.

Balaninæ, sub-family of, 175. characters of, 152.

Balanus, genus, 177. shell of, immediately after the metamorphosis, 41. supposed male of, 271. Ajax, 214. allium, 281. amaryllis, 279. amphimorphus, 494. amphitrite, 240. angulosus, 256. arctica patelliformis, 256. arcticus, 262. balænaris, 415. balanoides, 267. pupa of, 130. monstrous specimens with imperforate penis, 102. cementing apparatus of, 146. balanoides, 240, 493. bisulcatus, 293. Blainvillii, 231. borealis, 262. calceolus, 218. candidus, 277. Capensis, 209. carbonarius, 492. cariosus, 273. cassis, 218. cepa, 283. chelytrypetes, 394. clavatus, 261, 267. circinnatus, 492. communis, 231, 492. concavus, 235. cornubiensis, 231. corrugatus, 254. Coquimbensis, 227. costatus, 493. Cranchii, 231. crassus, 195, 493. crenatus, 261. crispus, 494. cylindraceus, 206, 235, 494. cymbiformis, 221. Cumingii, 335. declivis, 275. decorus, 212. delphinus, 494. dentiformis, 493. diadema, 417. discors, 227. dolosus, 295. d'Orbignii, 195. duploconus, 365. eburneus, 248. elongatus, 220, 261, 267. erisma, 296. fasciatus, 201. Finchii, 492. fistulosus, 267. flosculus, 290. galeatus, 104, 105, 220. geniculatus, 256. gigas, 210. glacialis, 261. glandula, 265. goissopomo, 495. Hameri, 277. Holgeri, 492. humilis, 495. imperator, 288. improvisus, 250. inclusus, 299. intertextus, 518. lævis, 227. lævis, 495. latiradiatus, 493. miser, 235, 494. Montagui, 308. navicula, 221. nigrescens, 210. nubilus, 253. ornatus, 493. ostrearum, 492. ovularis, 267, 494. patellaris, 259. patellaris, 494. pectinarius, 493. peregrinus, 492. perforatus, 231. upfilled parietal tubes of, 44. perforatus, 494. perplexus, 296. picos, 206. pictus, 493. plicarius, 493. plicatus, 337. pœcilus, 246. polythalamius, 392. porcatus, 256. porosus, 493. proteus, 492. psittacus, 206. punctatus, 267, 493. puncturatus, 337. pustula, 492. pustularis, 235, 493. pyramidalis, 494. quadrivittatus, 284. radiatus, 242, 494, 495. rhomboicus, 494. roseus, 279. rugosus, 261. sagittata, 493. Scoticus, 256. semiplicatus, 494. spongeosus, 308. spongicola, 225. spongites, 308. squamosus, 328, 494. stalactiferus, 329. stellaris, 494. striatus, 494. stultus, 216. sublævis, 493. sulcatinus, 293. sulcatus, 256, 493. terebratus, 285. tertiarius, 494. tesselatus, 256, 494. tintinnabulum, 194. varieties of, 201. tintinnabulum, eyes of, 93. nervous system of, 92. cementing apparatus of, 147. tintinnabulum, 195, 204, 206, 214, 493. trigonus, 223. tulipa, 195, 205, 277, 494. tulipiformis, 204. Uddevallensis, 277, 494. unguiformis, 296. varians, 298. verruca, 518. vestitus, 286. vinaceus, 213. virgatus, 494. vulgaris, 267. zonarius, 235, 494.

Ball, Dr., on the attachment of Chelonobia, 392.

Basis of shell, 49. cancellated in Bal. lævis, 230. perforated in Bal. terebratus, 285. hardly distinguishable in Bal. flosculus, 291. affected by adhering to corals, 301. surrounded by a ledge in Chthamalus, 452, 466, 467.

Bate, Mr. C., on the spermatozoa of cirripedes, 99. on the larva of cirripedes, 103. on the excavation of Verruca, 514, 518.

Bisexuality of cirripedes, 23.

Boring powers of, in Verruca, 512. in Alcippe, 549.

Boscia, genus, 354.

Bosquet, M., Monographie, &c. 526.

Branchiæ, 63. in Alcippe, 537.

Brewster, Sir D., on lime and animal matter, 552.

Bristles on membranes of shell and operculum, 59.

Bronn, list of Balanidæ in his Index Palæont., 173.

Burmeister on the rank of cirripedes, 17. branchiæ of Coronula, 64. labrum of Coronula, 77. reproductive system of cirripedes, 97, 100. larvæ in the second stage, 109. larvæ in the last stage, 114.

Cæca, ovarian, 100. to stomach, 85.

Calcar tergi, 52.

Caligus, nerves of, 88.

Canal, alimentary, 85.

Carapace, homologies of, 131. of pupa, 112. aborted in Proteolepas, 595, 603.

Carina, posterior compartment of shell, 39.

Catophragmus, genus, 485. connecting link between the Balanidæ and Lepadidæ, 41. imbricatus, 490. polymerus, 487.

Cement, tube of, proceeding from the pupal antennæ, 118.

Cementing apparatus in the pupa, 118, 122. in the mature animal, 133. in Platylepas, 426. in Xenobalanus, 442. in Proteolepas, 599. organs of, in crustacea, 151.

Cetopirus, genus, 397.

Chamæsipho, genus, 470. columna, 470. scutelliformis, 472.

Changes during growth in the Balanidæ, 128, 189.

Characters, variability of, 155, 184, 197. value of, in the Balanidæ, 154.

Chelonobia, genus, 382. caretta, 394. patula, 396. cementing apparatus of, 145. Savignii, 392. testudinaria, 392.

Chirona, genus, 177.

Chitine, 7, 58.

Chthamalinæ, sub-family of, 446. characters of, 152.

Chthamalus, genus, 447. antennatus, 460. cirratus, 461. dentatus, 463. fissus, 462. giganteus, 477, 192. glaber, 455. Hembeli, 465. intertextus, 467. scabrosus, 468. stellatus, 455. stellatus, 492.

Ciliæ, not present in the articulata, 516.

Circulation, 87.

Cirri, their muscles and movements, 71. their structure, 81. their reparation, 158. in Acasta, with variable hook-like teeth, 306, 311. antenniformed in Chthamalus, 453, 460. variability in numbers of segments in Tetraclita porosa, 332. structure of, variable in Chamæsipho columna, 472. with one ramus, converted into a triturating button in Alcippe, 542. abdominal in Cryptophialus, 575. none in Proteolepas, 587.

Cirripedia, their rank and affinities, 10 to 20.

Cirripedes, how their position is acquired, 127. young, changes in, 128. sessile, 33.

Clisia, genus, 496. striata, 519.

Clitia, genus, 496. verruca, 519.

Clysia, genus, 496.

Coldstream, Dr., on the shells of cirripedes, 33. on a clicking noise, made by cirripedes, 64.

Columellina, genus, 424. bissexlobata, 428.

Compartments of shell, number of, 39. structure of, 43.

Concholepas Peruviana, inhabited by Cryptophialus, 567.

Conia, genus, 321. depressa, 337. Lyonsii, 343. porosa, 329. radiata, 343. rosea, 335.

Conopea, genus, 177. remarks on, 190. elongata, 220. ovata, 218.

Corals, effect of attachment to, in Balanus, 301.

Coronula, genus, 397. balænaris, 415. cementing apparatus of, 135. barbara, 421. bifida, 423. bissexlobata, 428. Californiensis, 428. diadema, 417. nervous system of, 88. patula, 396. reginæ, 419. sulcata, 394. testudinaria, 392. tubicinella, 431.

Coronula, genus, 382, 424, 430.

Coronulinæ, sub-family of, 153.

Coronulites diadema, 421.

Creusia, sub-genus, 375. Childreni, 382. decorata, 382. grandis, 376, 381. gregaria, 376, 378. madreporarum, 367, 382. multistriata, 382. radiata, 382. spinulosa, 376. striata, 382. Strömia, 518. verruca, 518.

Creusia rayonnante, 362.

Creusia, genus, 354, 497.

Cross-impregnation of Cirripedes, 102, 197.

Crustacea, cementing organs of, 151.

Cryptophialus, sexes of, 23. minutus (female), 566. (male), 584.

Dana, Mr., on the classification of Crustacea, 11, 17. on centralisation in Crustacea, 19. on nerves of Caligus, 88. on the antennæ of the larvæ of cirripedes, 106, 114. on the conversion of mandibles into legs, 107. on the abortion of the segments of body, 111. on the distribution of Crustacea, 161, 167.

Daphnia, organs of hearing, 114. eyes of, 121. moulting of, 157.

Daracia, Genus, 354. monticulariæ, 372. Linnæi, 374.

Denticuli, on the parietal septa, 43.

Deposit, calcareous, inorganic in chamber of Alcippe, 552.

Depths at which cirripedes live, 163.

Diadema, genus, 397. bifida, 492. vulgare, 492.

Du Cane, Capt., on the larvæ of Crustacea, 108.

Edwards, Prof. Milne, on the classification of Crustacea, 11, 17. on the lengthening and shortening of the limbs in Crustacea, 14, 73. on the 'tige' and 'palpe' of the limbs, 83. on the sclerodermic plates of the Carapace, 35. on the Carapace, 131. on general classification, 529, 565.

Elminius, genus, 345. Kingii, 348. cementing apparatus of, 146. Leachii, 348. modestus, 350. plicatus, 351. simplex, 353.

Epidermis, so called, 58.

Epithelium of stomach, 86.

Epizoons (male), 27.

Euraphia, genus, 447. Hembeli, 465.

Excavation, powers of, in Verruca, 512. in Alcippe, 549.

Exuviation of the pupal membranes, 123. in the mature animal, 157. in relation to the habits of cirripedes, 56. anomalous in Isaura, 13.

Eye of larva in first stage, 104.

Eyes of pupa, 119. of pupa, their exuviation, 126. in pupa of Alcippe, 549. the metamorphoses of, in Cirripedes, 120. of Balanus, 93.

Female organs, 100.

Flabellum of limbs, 83.

Food of Cirripedes, 87.

Fouet of limbs, 83.

Fræna, ovigerous, homologous with branchiæ, 65.

Fræna, ovigerous, modified in Alcippe, 537.

Generation, organs of, 97.

Geography of Cirripedes, 159.

Geological history of Cirripedes, 172.

Glands for cement, 138.

Gnathites, structure and muscles of, 75, 77.

Goodsir, Mr., on the larvæ of Cirripedes, 103, 108. on his male Balanus, 271.

Gray, Dr., on the homologies of sessile and pedunculated Cirripedes, 34. on the Coronulinæ, 153. on marks on the shell of a Balanus, produced by growing on wood, 185. on the structure of Chthamalus, 448.

Growth of shell, 54. changes during, 128, 189. rate of, 156. of shell in Tubicinella, 436.

Habits of Cirripedes, 159.

Hancock, Mr., on the action of the cirri, 14. on the excavations of Verruca, 512, 516. on Alcippe, 530. on the excavations of Alcippe, 549.

Hanley, Mr. S., on Bal. Hameri, 277.

Hearing, organs of, 95.

Hectocotyle, 23.

Hepatic system, 86.

Hermaphrodite condition of Cirripedes, 23.

Hippolyte varians, larvæ of, 108.

History, geological, of Cirripedes, 172.

Homologies of Cirripedes, 102. of the carapace and valves, 131. of body in Proteolepas, 595.

Horner, Mr., on lime and animal matter, 552.

Horsford, Dr., on the setting of lime, 553.

Ibla, sexes of, 23.

Imbedment of Chelonobia in turtles, 390. of Coronula in whale's skin, 411.

Impregnation, mutual, of Cirripedes, 102, 197, 271.

Injuries, reparation of, 158.

Interbreeding possible in Cirripedes, 102, 197.

Isaura, not moulting its carapace, 13.

Jaws, movements of, 76.

Joly, M., on the Isaura, 13. on the larvæ of Caradina, 106.

Jones, Dr., on the liver in Daphnia, 86.

Jussieu, Adrien, on classification, 528.

Karsten on the testes and ovaria of Cirripedes, 98, 100. on supposed hepatic organs, 86.

Kölliker on the spermatozoa of Cirripedes, 99.

Labrum, structure of, 75. remarkable, in Alcippe, 540. moveable, in Cryptophialus, 572.

Lamellæ, ovigerous, 101. in Xenobalanus, 444.

Lamina, internal of wall of shell, cancellated, 213.

Larvæ, first stage, 103. second stage, 109. during their early stages, egg-like in Cryptophialus, 579. last or pupal stage, 110.

Leach, Dr., on the Coronulinæ, 153.

Legs of pupa, 121.

Leidy, Dr., on the eyes of Balanus, 94.

Lepadidæ, family of, 526.

Lepas angusta, 231. angustata, 231. australis, pupa of, 110. balanoides, 231, 240, 267. balanus, 231, 256. borealis, 251. caretta, 394. cariosa, 273, 329. cœrulescens, 342. columna, 470. costata, 256. crispata, 195. depressa, 455. diadema, 417. fascicularis, cement, float of, 118. fistulosus, 231. foliacea, 261, 277. fungites, 329. galeata, 220. Hameri, 277. minor, 240. mitra, 344. ore angustiore, 231. radiata, 240. patellaris, 259. porcata, 195. porosa, 329. psittacus, 206. punctatus, 455. purpurascens, 337. purpurea, 241. Scotica, 256. spinosa, 195. spongiosa, 308. spongites, 308. stellata, 455. striata, 518. Strömia, 518. testudinaria, 392. tintinnabulum, 194, 235. tulipa, 204, 277. verruca, 518.

Lesson on the Triton, 158.

Limbs of pupa, 121.

Limbus occludens in Pyrgoma, 54.

Lime, tendency to harden with animal matter, 552.

Limulus, nervous system of, 88, 90.

Linnæus on the Triton, 158.

Lithotrya, powers of boring, 535.

Liver, 86.

Lyell, Sir C., on Bal. Uddevallensis, 277.

Male organs, 97. of Alcippe lampas, 555. of Cryptophialus minutus, 584.

Males of Cirripedes, 23. of Cirripedes, not of much classificatory importance, 566, 586.

Manatee, with Platylepas attached to the skin, 427.

Mandibles structure of, 76, 79. reversed in Proteolepas, 589.

Maxillæ, structure of, 76, 80. reversed in Proteolepas, 590.

Megatrema, genus, 354. Anglica, 360. semicostata, 374.

Membrane, covering the shell, 58. opercular, 58.

Messula, genus, 177.

Metagenesis, 124.

Metamorphoses in the Thoracica, 102. of Alcippe, 548. remarkable, in Cryptophialus, 579.

Moulting of the pupal membrane, 123. in the mature animal, 157.

Mouth, structure of, 74, 78. of pupa, 121. none in the male Alcippe and Cryptophialus, 562, 585. suctorial in Proteolepas, 589.

Movements of the cirri, 71.

Muscles of attachment of the body to the operculum, 68. of the sack, 62. of the thorax, 69. of the cirri, 71. of the jaws, 76. of sack, weak in Chelonobia, 389.

Nerves splanchnic, 91.

Nervous system, 88.

Nobia, genus, 354. grandis, 365.

Nomenclature, rules of, 204.

Ochthosia, genus, 497. Stroemia, 519.

Octomeris, genus, 482. angulosa, 483. augubra, 483. brunnea, 484. Stutchburii, 483.

Œsophagus, 85. in the pupa, 121. with teeth, in Cryptophialus, 577.

Operculum, 50. remarkable, in Pyrgoma, 356. remarkable, in Verruca, 497.

Orders of Cirripedes, 20.

Organs, acoustic, 95. of pupa, 113. of reproduction, 97. for cementing, 133. in the pupa, 122.

Orifice of shell, 38.

Otolithes absent in Crustacea, 97.

Ova, sizes of, 101.

Ovaria, 100. incipient, in pupa, 122. occupy a chamber in the shell in Coronula, 411. in Proteolepas, 597.

Owen, Prof., on Metagenesis, 124. on vegetative repetition, 20.

Pachylasma, genus, 475. structure of alæ, 36. giganteum, 172, 477. aurantiacum, 480.

Palpi, structure of, 75. absent in Alcippe, 540. peculiar in Cryptophialus, 572. in Proteolepas, 590.

Parasite, allied to Bopyrus, 102.

Parietes of shell, 43. internal lamina of, cancellated, 213. perforated in Acasta, 305. with numerous rows of pores in Tetraclita, 323. much folded in Coronula, 399.

Penis, probosciformed, 99. imperforate, 102, 271. its reparation, 159. of wonderful length in Cryptophialus, 586.

Perforations in shell of Acasta, 305.

Phyllosoma, affinities to cirripedes, 18.

Platylepas, genus, 424. bissexlobata, 428. decorata, 429. cementing apparatus of, 143. pulchra, 428.

Pœcilasma Kæmpferi, 499.

Pollicipes compared with sessile cirripedes, 34, 41, 52.

Polylepas, genus, 397.

Polytrema, genus, 321.

Position of cirripedes, how acquired, 127.

Potash, caustic, action on shell, 56.

Primordial valves, 129.

Prosoma, part of thorax, 67.

Proteolepas bivincta, 589.

Pupæ of cirripedes, 110.

Pupa without natatory legs in Cryptophialus, 580.

Pyrgoma, genus, 354. Anglicum, 360. cancellatum, 362. conjugatum, 364. corymbosa, 374. crenatum, 370. dentatum, 369. grande, 365. lobata, 362 milleporæ, 367. monticulariæ, 372. spongiarum, 374. stellata, 374. Stokesii, 361. sulcatum, 360, 492. undata, 492

Radii, structure of, 37, 45. remarkable, with outer lamina of great thickness in Chelonobia, 385. compound in Coronula, 405. in Xenobalanus, 441.

Rami of the cirri, their movements and homologies, 71, 83. modified in Alcippe into triturating organs, 542.

Range, geographical, of cirripedes, 159.

Rathke, on the position of the anus in young Crustacea, 109. on the cementing organs of Crustacea, 151.

Rectum, 87.

Reparation of injuries, 158.

Reproduction of cirripedes, 97.

Respiration of cirripedes, 64.

Rostrum, anterior compartment of shell, 39. not symmetrical in Chelonobia caretta, 383. compounded in Chelonobia, 386. in Pachylasma, 478, 481. not quite medial in Platylepas, 424.

Rules of nomenclature, 204.

Sack, 61. muscles of, 62. formation of, 124.

Sacks, acoustic, 95. olfactory, 97

Savignium, genus, 354.

Scalpellum, sexes of, 23. vulgare, larvæ of, 103

Schödler, on organs of hearing in Daphnia, 114.

Schumacher, date of memoir, 321.

Scuta, their structure, 51.

Scutum, with horny articular ridge in Chelonobia, 388. remarkable from great adductor ridge and occludent ledge in Pyrgoma, 356. fixed in Verruca, 502.

Sections, transverse, of shells of Balanidæ, 39.

Segments of body in cirripedes, 111, 125. in Alcippe, 537. in Cryptophialus, 571.

Senses of cirripedes, 94.

Septa, longitudinal, of the parietes, 43.

Sexes of cirripedes, 23.

Sheath of shell, 38, 48. peculiar in Tubicinella, 432. remarkable in Chelonobia, 385.

Shell of a sessile cirripede compared with the shell of the Lepadidæ, 34, 41, 52. of sessile cirripede compared with the carapace of Crustacea, 35. elements of, 37. sheath of, 38, 48. orifice of, 38. compartments of, 39, 43. immediately after the metamorphosis, 41. walls of, or parietes, 44. radii of, 37, 45. alæ of, 37, 47. basis of, 49, operculum of, 50. growth of, 54. minute structure of, 57. membranes of, 58. sack of, 61. with tubular perforations in Chamæsipho, 473. almost rudimentary in Xenobalanus, 441. asymmetrical in Verruca, 499. minute structure of, in Verruca, 506.

Shells of mollusca excavated by Verruca, 512. excavated by Alcippe, 549.

Siebold, Von, on Syngamus trachealis, 23. on the abdomen of cirripedes, 65. on the cæca of the stomach in Crustacea, 86. on the vision of cirripedes, 94. on the acoustic organs of Crustacea, 97. on the spermatozoa of cirripedes, 99. on the eyes of cirripedes, 121.

Siphonicella, genus, 438.

Size of cirripedes in relation to temperature, 162.

Sowerby, Mr. G. B., on the species of Balani having cup-formed bases, in the southern hemisphere, 192.

Sowerby, Mr. G. B., jun., on an inorganic deposit in connexion with a Pholas, 553.

Species, variability of, 155, 184, 197.

Spermatozoa, 98.

Spur of tergum, 52.

St. Ange, M. M., on the mouth of cirripedes, 19, 76. on the reproductive system of cirripedes, 97, 100. on the nervous system, 92.

Stomach, 85. none in Proteolepas, 596. none in the male Alcippe and Cryptophialus, 562, 585.

Stomopoda, affinities to cirripedes, 19.

Straus, on the affinities of cirripedes, 9. on the moulting of Daphnia, 157.

Structure, microscopical, of shell, 57. peculiar in Verruca, 506.

Stutchbury, Mr., on the shell of Chelonobia, 386.

Syngamus trachealis, 23.

System, muscular, of the body and cirri, 62, 68, 71, 76. alimentary, 85. circulatory, 87. nervous, 88. reproductive, 97.

Temperature, effects of, on cirripedes, 161.

Terga, their structure, 51.

Tergum, occludent ledge and shape of, in Pyrgoma, 356. fixed in Verruca, 503.

Testæ valvæ, 39, 43.

Testes, 97. development of, in Proteolepas, 598.

Tetraclita, Genus, 321. cœrulescens, 342. costata, 339. porosa, 328. upfilled parietal tubes of, 44. purpurascens, 337. radiata, 343. rosea, 335. serrata, 333. squamulosa, 329. vitiata, 340.

Thoracica, order of, 21, 30.

Thorax of the Balanidæ, 66. of pupa, 85. rudimentary, in the male Alcippe, 562.

Tige of limbs, 83.

Triton of Linnæus, 158.

Tubicinella, genus, 430. cementing apparatus of, 143. trachealis, 431. balænarum, 431. Lamarckii, 431. major, 431. maxima, 172, 438, 492.

Turtles, with their carapaces perforated by Chelonobia, 391. with Platylepas attached, 427.

Unisexuality of cirripedes, 23.

Vagina or sheath, 38, 48.

Valves, opercular, 50. of shell, 39, 43. primordial, 129. homologies of, 131.

Van de Hoeven on Limulus, 88, 90.

Variation of characters, 155, 184, 197. in Tetraclita, 327. in Chthamalus, 459.

Verruca, genus, 496. cancri Americani, 396. lævigata, 520. nexa, 522. prisca, 525. Spengleri, 521. Strömia, 518.

Verruca testudinaria, 392.

Verrucidæ, family of, 495.

Vesicle, acoustic, 95.

Vesiculæ seminales, 98.

Vesicula seminalis, compound in Proteolepas, 598.

Vision of cirripedes, 94.

Wagner, R., on the reproductive system of cirripedes, 97, 99.

Walls of shell, 43.

Water, brackish, effects of, on cirripedes, 163.

Whales' skin, growth of, into the shells of Coronula, 413. perforated by Tubicinella, 436.

Xenobalanus, genus, 438. globicipitis, 440.

Zenker on the eyes of Daphnidæ, 121.

Zoosperms, 98.

PLATES.

Detailed Transcriber's Notes

Words which were in italics in the original book are surrounded by underlines (italic). Words which were originally printed in small caps are in ALL CAPS. Obvious misprints have been fixed. Archaic and unusual words, spellings and styling have been maintained when they are used consistently. Spelling has been standardized within the book where one spelling was predominant, even if it is not in common usage. Inconsistent spelling and hyphenation has been maintained when there was not a predominant spelling. Details of the changes follow.

No attempt has been made to correct the capitalization or standardize the italicization of biological names--they are left as in the original.

All of Darwin's errata have been applied to the text, except the one on page 255. It was not applied because the wording is not obvious.

This book was published in two volumes, of which this is the second. The first volume was released as Project Gutenberg ebook #31558, available at http://www.gutenberg.org/ebooks/31558.

Details of the Changes

Page vii, footnote 1: du terrain Crétacé du D. de Limbourg In the original book: du terrain Crétacée du D. de Limbourg

Page 4: the shell, without the operculum being removed, In the original book: the shell, without the operculum be removed,

Page 5, footnote 3: by some authors as "intersticia." In the original book: by some authors as "intersticia".

Page 7: carrying two multiarticulated rami In the original book: carrying two multi-articulated rami

Page 8: interjection (!) In the original book: interjection [!]

Page 9: biramous, multiarticulated limbs In the original book: biramous, multi-articulated limbs

Page 11: knowledge of the class In the original book: knowlege of the class

Page 12: first and second pairs of antennæ In the original book: first and second pairs of attennæ

Page 20: what has happened to one organ In the original book: what has happenend to one organ

Page 30: ORDER I.--THORACICA. In the original book: I.--ORDER THORACICA.

Page 33. The table of contents has been completely restructured, to make the entries match (or compromise with) the titles in the text.

In this ebook: Structure of the alæ Structure of the sheath In the original book: Structure of the alæ and sheath

In this ebook: Structure of the opercular valves (scuta and terga) In the original book: Structure of the scuta and terga

In this ebook: Growth of whole shell and microscopical structure In the original book: Growth of whole shell and minute structure of valves

In this ebook: Muscles of sack In the original book: Sack, muscles of

In this ebook: Movements and muscles of the cirri In the original book: Cirri, muscles of

In this ebook: Olfactory sacks In the original book: Olfactory organs

In this ebook: Larva, first stage In the original book: Larva, first stages

In this ebook: Larva, second stage Originally this TOC entry was not present in the book.

In this ebook: Affinities, classification, variation In the original book: Classification and variation

Page 34. Inserted missing title (which appeared in the TOC): Structure of Shell.

Page 37: in all cases (as is obvious in Pachylasma) In the original book: in all cases (as is obvious in Pachylasma)

Page 40: the upper lateral valves alternate In the original book: the upper Lateral valves alternate

Page 45: owing to its midrib, is generally thrust In the original book: owing to its mid-rib, is generally thrust

Page 45. Inserted missing title (which appeared in the TOC): Structure of the Radii. and left the original paragraph title as it was: Radius.

Page 47: and of the recipient furrow in Octomeris (Pl. In the original book: and of the recipient furrow in Octomeris (Pl.

Page 47: Structure of the Alæ. In the original book: Alæ.

Page 48: Structure of the Sheath. In the original book: Sheath.

Page 49: Structure of the Basis. In the original book: Basis.

Page 51: Structure of the Opercular Valves (Scuta and Terga). In the original book: Opercular Valves.

Page 61: Muscles of Sack. In the original book: Sack; muscles of, &c.

Page 62: can only act as depressores; In the original book: can only act as depressors;

Page 65: Balanidæ are the ovigerous fræna of the Lepadidæ In the original book: Balanidæ are the ovigerous fræna of the Lepadidæ

Page 65. Inserted title from the TOC: Thorax and Body. and demoted the existing title: Parts of the body included within the shell or carapace. to the head of the next paragraph.

Page 67: p. 440, (foot-note), consider the articulated In the original book: p. 440, foot-note), consider the articulated

Page 68: Muscular System.

Attachment of the Body to the Shell. In the original book: Attachment of the Body to the Shell. Muscular System.

Page 76: there is no trace of any labrum In the original book: there is no trace of any labium

Page 77: (Pl. 26, figs. 3, 4, c^1; In the original book: (Pl. 26, figs. 3, 4, c 1;

Page 78: pairs of gnathites, which latter have only In the original book: pairs of gnathites; which latter have only

Page 79: thickened membrane (fig. 3, c^1) In the original book: thickened membrane (fig. 3, c 1)

Page 79: thickened membrane (c^2), the basal In the original book: thickened membrane (c 2), the basal

Page 80: piece of membrane (c^1) represents In the original book: piece of membrane (c 1) represents

Page 81: middle segment (fig. 4, a^1) of each maxilla In the original book: middle segment (fig. 4, a 1) of each maxilla

Page 81: this latter (a^2) is separated from In the original book: this latter (a 2) is separated from

Page 81: There are always six pairs; each biramous In the original book: There are always six pair; each biramous

Page 83: they carry as many as ten pairs in a In the original book: they carry as many as ten pair in a

Page 84: in the sub-genus Acasta, in which, differently In the original book: in the sub-genns Acasta, in which, differently

Page 85: developed into strong, downwardly curved teeth In the original book: developed into strong, downwardly-curved teeth

Page 89: The nerves (Pl. 27, fig. 1, r^5, r^6) In the original book: The nerves (Pl. 27, fig. 1, r 5, r 6)

Page 89: outer larger pair (r^1) entering In the original book: outer larger pair (r 1) entering

Page 93. Inserted missing title (which appeared in the TOC): Eyes and Vision.

Page 97: Male Organs of Generation. In the original book: Reproductive System.

Male Organs.

Page 98: B. Perforatus and in the Chthamalus, that In the original book: B. Perforatus and in the Chthamalus, that

Page 99: including the prosoma: in Pachylasma and in In the original book: including the prosoma: in Pachylasma and in

Page 100: Female Organs of Generation. In the original book: Female Organs. was a paragraph title.

Page 100: distinctly in Balanus, Tetraclita, and Coronula, the In the original book: distinctly in Balanus, Tetraclita, and Coronula, the

Page 103: Larva, First Stage. In the original book this was a paragraph title.

Page 103: the larva (Pl. 29, fig. 9) In the original book: the larva (Pl. 29, (fig. 9)

Page 104: to the eye, we see, in Scalpellum vulgare, In the original book: to the eye, we see, in Scalpellam vulgare,

Page 104. Applied Darwin's errata: In Balanus galeatus, in the immature In the original book: In Balanus elongatus, in the immature

Page 105. Applied Darwin's errata: Lepadidæ; but in Balanus galeatus In the original book: Lepadidæ; but in Balanus elongatus

Page 106: the large second pair remains thus In the original book: the large second pair remain thus

Page 110: Larva in the Last or Pupal Stage. In the original book: Larva in the third or Pupal Stage.

Page 120: though enclosed fairly within the carapace In the original book: though inclosed fairly within the carapace

Page 121: these latter may possibly be multiplied into In the original book: these latter may possible be multiplied into

Page 126. Inserted missing title (which appeared in the TOC): Act of Metamorphosis.

Page 132: separation of the three cephalic segments. In the original book: separation of the three caphalic segments.

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