On the structure and affinities of the "Tabulate corals" of the Palaeozoic period, with critical descriptions of illustrative species

Front matter

I

^a^i£S

OF

Chapter I. The Classification And Affinities Of The " Tabulate

CORALS."

The " Tabulata',' as originally understood, constitute one of the four primary divisions of the Zoantharian Actinbzoa, as laid down and defined by Milne- Edwards and Haime in their great works upon the fossil Corals (Brit. Foss. Corals, Introduction, 1850; and Polypiers Foss. des Terr. Pal., 1851). In this division was included a larcre assembla8;-e of Corals, rancrlne from the Silurian period to the present day, and often of very diverse structure, but characterised by the possession of well-developed " walls," by the separation of the visceral cavities of the corallites into distinct chambers by transverse partitions or " tabulae," and by the rudimentary condition of the " septa." The distinguished French zoophytologists just quoted remark of this division of the Corals, that its principal character " is founded on the existence of the lamellar diaphragms that close the visceral chamber of the corallites at different heights, and differ from the dissepiments of the Asti'ceidcE by not being dependent on the septa, and forming as many complete horizontal divisions extendinfy from side to side of the general cavity, instead of occupying only the one or two loculi. It is also to be remembered that the septal apparatus, though more or less rudimentary, has the same general mode of arrangement as in the preceding sub-orders " {Aporosa and Perforata), " and never presents the crucial character which we shall find in the Zoantharia Riigosa!' They also divide the " TabiUata " into the following four families, comprising the under-mentioned

Fani. I. MiLLEPORiD^. — Corallum principally composed of a very abundant

coenenchyma, distinct from the walls of the corallites, and of a tubular or

cellular structure. Septa not numerous ; tabulae numerous and well formed.

. pora, M'Coy ; Plasmopora, Edw. and H,; Fropom, Edw. and H. ; Axopora,

Edw. and H. ; Lobopora, Edw. and H.

Fam. II. Favositid/E. — Corallum essentially formed by lamellar walls, with little or no coenenchyma. Visceral chambers divided by numerous and well-developed complete tabular.

Tribe i. Favosithnc. — Corallum massive. Walls perforated. Septa rudimentary. No coenenchyma. Genera — Favositcs, Lam. ; Michelinia, De Kon. ; Koninckia, Edw. and H. ; Alveolites, Lam. Tribe 2. Chcetetince. — Corallum massive. Walls not perforated. Neither septa nor coenenchyma. Genera — Chcetetes, Fischer; Dania, Edw. and H ; Ste/iopora, Lonsd. ; and Constellaria, Dana. Tribe 3. ILalysitincE. — Corallum composed of corallites constituting vertical laminae or fasciculi, but more or less free laterally, and united by means of connecting tubes or mural expansions. Walls well developed, and not porous. Septa distinct, but small. Genera — Balysites, Fischer; Harmodites, Fischer (subsequently abandoned for Syringopora, Goldf.), and T/iecostegites, Edw. and H. Ti-ibe 4. PocilloporincB. — Corallum massive, gibbous, or subdendroid, with thick imperforated walls, forming towards the surface an abundant compact coenenchyma. Septa quite rudimentary. Genus — Pocillopora, Lam.

Fam. III. Seriatoporid^. — Corallum arborescent or bushy, with an abundant compact coenenchyma. Visceral chambers filling up by the growth of the columella and the walls, and showing but few traces of tabulae. Genera — Seriatopora, Lam. ; Dendrop07-a, Michelin ; Rhabdopora, Edw. and H.

Fam. IV. Thecid^e. — Corallum massive, with an abundant, compact, spurious coenenchyma, produced by the septa becoming cemented together laterally. Tabulas numerous. Genus — Thecia, Edw. and H.

Various additions, modifications, and improvements in the above classification of the " Tabulata'' were made by Milne-

Edwards and Haime during the progress of their classical monograph on the Fossil Corals of Britain ; many new genera were added ; and the tribe of the StylophyllincE, to include the curious Cretaceous genus Stylophyllum, Reuss, was inserted in the family of the FavositidcE. Most of the changes here indicated, which it would be needless to point out in detail, are to be found incorporated in the systematic account of the " Tabulata" given by Milne-Edwards in his masterly ' Histoire Naturelle des Coralliaires' (vol. iii., i860).

The first serious attack upon the classification of Milne-Edwards and Haime, and upon the position of the " Tabulata," ys!3.s made by Professor Louis Agassiz, who in 1857 examined the living animal of Millepora, and arrived at the conviction that this genus was truly Hydrozoal (Amer. Journ. Sci. and Arts, ser. 2, vol. xxvi. p. 140, 1858; Proc. Bost. Soc. Nat. Hist, vol. vi. p. 373, 1859). This conclusion has since been fully borne out by the researches of Mr Moseley, to be subsequently referred to ; but Professor Agassiz based upon his discovery a further conclusion which certainly was not warranted by the known facts — namely, that the Hydrozoal nature of Millcpora sufficiently proved all the so-called '* Tabulate Corals " to be referable to the Hydrozoa.

Shortly after the publication by Professor Agassiz of his unexpected discovery as to the Hydrozoal nature oi Millcpora, Professor Verrill investigated the anatomy of the " Tabulate " genus Pocillopora, Lam., and showed that the animal of this Coral was a true Zoantharian, referable to the Aporosa, and allied to the OcttlinidcE (Review of the Corals and Polypes of the W. Coast of America, Trans. Conn. Acad., vol. i. pp. 2, 523, 1870; and Affinities of the Tabulate Corals, Proc. Amer. Assoc, for Adv. of Science, p. 148, 1867). Professor Verrill likewise, even at this date (Trans. Conn. Acad., loc._ cii.), powerfully supported the view that the Favositidcs are not only true Adinozoa, but that they are really referable to the Zoantharia. In the year 1872 the same high authority published an important memoir upon " The Affinities of the Palseozoic Tabulate Corals with existing Species" (Amer. Journ. Sci. and Arts, sen 3, vol. iii. p. 187), in which he forcibly pointed out that the discovery of the Hydrozoal nature oi Miikpora, Lam., did not necessarily carry with it the reference of the whole of the " Tabulata " to the Hydrozoa. On the contrary, he affirms that, " as to the great majority of the ' Tabulata ' and ' Rugosa,' there can no longer be any reasonable doubt " that they are essentially animals of the same nature as " the existing Corals " {i.e., Zoantharid). The family of the Pocilloporidoe is further established for the reception of Pocillopora and its allies ; CohimnaiHa is regarded as either a member of the Ast7'(Eid(E, or as referable to a closely allied family ; and the FavositidcB are merged with the Poritidce, doubt being expressed as to whether the group can be retained as even a sub-family.

In the year 1872, also, was published the admirable " Third Report on the British Fossil Corals," by Professor Martin Duncan, which was laid before the British Association for the Advancement of Science in 1871, and published in the Report of the Association. In this important memoir Professor Duncan deals very largely with the structure and affinities of the " Tabulate Corals" — his wide knowledge of both living and extinct Actmozoa rendering his views upon this subject particularly valuable and suggestive. Various of these views will be noticed subsequently ; and it will be sufficient to state here that he retains the " Tabulata^' of Edwards and Haime as a great division of the Zoaiitharia, subdividing it as shown in the followine table : —

Section Tabulata.

Families.

f Milleporidce. Ccenenchyma cellular.

With ccenenchyma, . . | AcroporidcB. Ccenenchyma compact.

i Fazwsitidce. Walls perforated.

Without ccenenchyma, . . \ LLalysitida;. Walls imperforate.

' AIveolJtid(t. Septa tridentate.

CLASSIFICA TION.

MlLLEPORID^,

acroporid^, Favositid^,

HALYSITIDiE,

Alveolitid^, Incertse sedis.

Genera.

Millcpora.-^

Hdiolitcs, Hcliopora, Folytreinacis.

Propora, Flastnopora, Thecia.

Lyellia.

ThecostegUes. ^ Axopora.

Acropora, Scriatopora, Podllopom, Dendropora, Rhabdopora. / Favosites, Koninckia, Favositipora, \ Michelinia, Rmmeria^ Eminoiisia. j Syringopora. ' Aiilopora.

Halysites.

Stylophyllum.

C/toiiostegites.

Cohcmnaria.

Beatunontia.

Alveolites.

Ca'iiites. ( Fistulipora. \ Fletcher ia.

Alcyonaria.

Ch{Etet£s, Monticulipora, Dania, Stellipora, Labcchia.

Another very important memoir upon the " Tabulate Corals " was published in 1873 by Dr Gustav Lindstrom (Nagra anteckningar om Anthozoa Tabulata, Ofversigt af. Kongl. Vetensk. Akad. Forhandl., 1873. Translated in the Ann. and Mag. Nat. Hist, sen 4, vol. xviii. p. i, 1876). In this paper the distinguished Scandinavian palseontologist entirely abandons the ''Tabttlata'' of Edwards and Haime as a distinct division of the Corals ; Labeckia, E. and H., is placed among the Hydrozoa, near to Hydractinia ; Monticulipora, D'Orb., Fistulipora, M'Coy, and some other forms, are regarded as Polyzoa ; the Favositidce are placed in the Poritidcu, among the Perforate Corals ; the Heliolitidce are considered as forming a

Mn a note, Dr Duncan adds that though not satisfied (1872) that Rlillepora is a Hydrozoon, he has great doubt about its Madreporarian affinities. He also points to the extremely close relation betv/een Heliolites and Heliopora, since so entirely confirmed by Mr Moseley.

special group of uncertain zoological position ; ColiLmnaria, Goldf., is placed among the Cyathophyllidis, in the section of the Rtigosa; Flctcheria, E. and H., and Michelinia, De Kon., are referred to the CystiphyllidcB ; and Syringopora, Goldf., is regarded as a Rugose Coral, allied to LitJiostrotioii or DipJiyphyllum. I shall have occasion to notice many of the views expressed by Dr Lindstrom in greater detail in dealing with the families and genera of the Palaeozoic Tabulate Corals ; and the general results of his investigations will be best understood if I append here the following list, in which the various genera of the " Tabulata^' of Edwards and Haime are referred to what Dr Lindstrom considers to be their true place in the zoological system : —

Name of Genus.

To be removed to

Millepora,

Hydrozoa ?

Heliopora,

Alcyonaria (Moseley).

Folytremads, Heliolitcs, .

Alcyonaria.

Lleliolitidce. (special family).

FistuUpora,

J Some species to Heliolites ; others 1 to the Folyzoa.

Plasviopora,

Heliolitid(B.

Fropora, .

( ILeliolitidce (probably inseparable \ from Flasmopora).

Lyellia,

HeliolitidcE.

Axopora, .

Hydrozoa ?

Battersbyia.,

Astrceidce (Duncan).

Favosites ) Emmonsia J

{ Sub-family Favositince of the Pori- \ tidcB.

Michelinia,

CystiphyllidcB.

Alveolites., .

Partly Favositime, partly Folyzoa.

Rcemeria \ Koiiinckla J

Favositiim.

C/icetetes

Montkidipora Dania

Folyzoa.

Stellipora

Dekayia, .

Folyzoa ?

Beaumoiitia,

Favositime.

Labechia, .

Hydrozoa.

Sfylop/iylltim,

Hydrozoa ?

Halysites, .

Heliolitidce.

SyrmgoponXy

•

j Vicinity of Lithostroiion and Diphy \ phylluin.

CLASSIFICA riON.

Name of Genus.

Thccosicgites, Chofwstcgites, Fletcheria, Pocillopora, Cxnites, Seriatopora, Thecia, Columnaria,

In a paper published by IV'

To be removed to He/iolitidcE.

Michclinia.

Cystiphyllidcc.

Ociili/iidcc (Verrill).

Polyzoa ?

Oculinidce ?

Hcliolitidce ?

Cyathophyllidce.

G. Dollfus in 1875 (Comptes

Rend., t. Ixxx.), the HcliolitidiB are regarded as unquestionably the representatives of the recent MilleporidcB — a view which Mr Moseley's researches have rendered altogether untenable ; and the PocilloporidcB are regarded, along with the preceding, as Hydrozoa — an opinion which the researches of Professor Verrill have sufficiently disproved. Syn'ingopora, Halysiies, Aulopora, and allied forms, are regarded as being either Poly son allied to Hippothoa and Idmonea, or else Alcyoiiaria. The family of the Chcetetidce is considered as having a direct relationship with the Jurassic Polyzoa of the genus Hetei^opora and the Cretaceous Radiopora. The Favositidce are regarded as most probably truly referable to the Polyzoa, the " mural pores " being compared with the intercellular pores of certain EscharcB and Lepralicc, and of some of the Cyclostomatous Polyzoa {Fwigella and Heteroporclld). It is clear, however, that the author's conception of the real structure of the FavositidcB has been grounded upon very imperfect materials. Lastly, Dendropora and Ti^ackypora — which we now know to be true members of the FavositidcE — are placed among the Polyzoa, and are regarded as allied to Horncra.

In 1876 Mr Moseley published his exceedingly important papers on the anatomy of the recent Millepoi'a and Heliopora (Notes on Two Species of Millepora, &c., Phil. Trans., 1876; Structure of a Species of Millepora occurring at Tahiti, Ann. and Mag. Nat. Hist., 1876; Structure and Relations of the Alcyonarian Heliopora cserulea, Phil. Trans,, 1876), which at once threw a flood of light upon the subject of the structure and affinities of the Palceozoic ''Tabulatay I shall have as'ain to refer to the investigations of Mr Moseley, as published in the above-mentioned and later memoirs ; and I shall merely say here that their general result was to complete the disintegration of the "• Tabiilata'' of Edwards and Haime, and to fairly remove from the Zoautharia certain groups that had previously been referred to this order of the Actinozoa. Thus, Millepora and its allies, as formerly asserted by Agassiz, are definitely proved to be true Hydrozoa, in which class they form, with the Stylasteridcs, the new order of the Hydrocoi^allincs ; Heliolitcs and its numerous allies, instead of being relations of Millepora, are shown conclusively to be Actinozoa, but to be at the same time referable to an unsuspected order of this class — namely, to the Alcyonaria ; while various familiar types of the Palaeozoic '"Tadtilala" are brought by these discoveries into more or less probable relationships with either the Hydrozoa or the Alcyonaria; and light of the most important character is afforded as to certain structural features in the Palaeozoic types, which have hitherto proved obscure or inexplicable.

In the article "Corals" in the ' Encyclopsedia Britannica ' (9th ed., vol. vi., 1877), I gave a short account of the then existinof state of our knowledo-e as to the structure and affinities of the "Tabulate" Corals. In this article the researches of Moseley are accepted ; the Favositidce are referred with some doubt to the Perforate Zoantharia ; the Chcstetidce are separated from the FavositidcSy and regarded as possibly Alcyonarian; the Syringoporidce are shown to have affinities with the FavositidcB ; and the conclusion is arrived at, that if any forms can be retained as a " Tabulate " order of the Zoantharia, it is probably those represented by Syringopora and Halysites, with their allies.

Lastly, Professor Zittel (Handbuch der Paleeontologie, Bd. i. Lief, ii., 1879) accepts in the fullest sense the abolition of the "Tabulata" of Milne-Edwards and Haime, and disposes of the members of this group in different directions. Millepora and its allies are placed, as is proper, in the Hydrozoa — as also, with less reason, is LabccJiia; the family of the Favositidce is referred, as is also probably correct, to the Perforate Corals, and is regarded as a sub-family of the Poritida^, Koninckia being removed from it, and placed with Alveopora in another sub-family (the Alvcoporimr) of the same group ; Syringopora, Aulopoi'a, Halysites, and their allies, are placed (without sufficient reasons adduced) among the Alcyonaria, in the family of the TiibiporidcB ; and the ChcBtetidce are entirely excluded from the Actinozoa, being presumably regarded as truly belonging to the Polyzoa.

The preceding historical sketch is necessarily extremely brief and imperfect, the limited space at my disposal not allowinor it to be otherwise ; but it will be sufficient to show the principal tendencies of the more recent researches of naturalists and palaeontologists with regard to the old group of the " Tabulate Corals." These researches, though still incomplete, are so far advanced that the abandonment of the ''Tabulata'' as a distinct group of the Zoantharia can hardly be avoided ; while the removal elsewhere of some of the principal forms previously included under this head is already a fact accomplished. It is, indeed, now quite clear that the chief character relied upon by Milne-Edwards and Haime, in their definition of the ''Tabulata'' — namely, the presence of "tabulae" — is one of very limited classificatory value. Thus, tabulae occur in Pocilloi)ora, Cyathophora, Cwlasircea, Claiisastrcea, and occasionally in Lophohclia, among the Zoantharia Aporosa ; in Alveopora, and the allied Favositipora, among the recent Zoantharia Perforata ; in Heliopora and its allies, in the Alcyonaria, as well as occasionally in Tubipor-a ; in the great majority of the Rugose Corals ; in Millepora and its allies among the Hydrozoa; and lastly, in a few extinct types of the Polyzoa {e.g., Radiopora and Heter^odictya). The mere fact of the occurrence of tabulae in so many forms of such diverse zoological affinities, is sufficient proof that these structures cannot be used in forming a classification of the Corals; but it is at the same time conclusive that the "tabulae" of these different types, though undistinguishable in appearance and performing identical functions, lo TABULATE CORALS.

cannot be precisely and in all cases homologous structures. With regard to the " tabulae " in the true Adinozoa, Professor Verrill concludes that " they are formed after each discharge of ova : the vacuity thus produced, being useless, is cut off from the visceral cavity above it by the formation of a septum. Therefore, if the eggs be discharged from all the radiating chambers simultaneously, or if from any other cause the polyp abandons all the chambers simultaneously, it is obvious that a complete septum or transverse plate will be formed across the entire tube ; but if the eggs be discharged at different times from the ovaries occupying the various radiating chambers, the septa formed below them in the different chambers will not be coincident, or exactly at the same level in all. It would seem, therefore, that the existence or non-existence of complete transverse plates is simply a matter of periodicity in the discharge of ova" (Amer. Journ. Sci. and Arts, ser. 3, vol. iii. p. 187). Dr Lindstrom has further adduced a considerable body of evidence in support of the view that the " tabulae " are only a modification of the endothecal "dissepiments" (Ann. and Mag. Nat. Hist, ser. 4, vol. xviii. pp. 2, 3). That this is the case in certain instances (such as Ccelastrcsa, Verrill) seems quite unquestionable; and it is indeed easy to see how the simultaneous production of dissepiments in all the intermesenteric chambers, at one level, would give rise to a structure entirely undistinguishable from a " tabula." There are, however, some considerations which should not be lost sight of, before it is concluded that the " tabulae " of the tabulate Actmozoa are merely modified interseptal dissepiments. Thus it is to be remembered that in the Rugose Corals there is generally a simultaneous development of both these structures, and that the "tabulae" are best developed in the axial region of the visceral chamber, into which the septa either only penetrate slightly {Dip/iyp/iylluin) or do not enter at all {Amplexus), and in which, therefore, "dissepiments" are either scanty or totally absent. Again, in various members of the Favositidcs, the septa are obsolete ; and there are therefore necessarily no " interseptal dissepiments,"

in the ordinary acceptation of this term, though the " tabulae " are well developed. Moreover, it begs the question at issue to speak of the vesicular plates of the Cystiphyllidce as being of the nature of " crowded and regular horizontal dissepiments I' which simulate "tabulae;" since it is just as likely that they are crowded and anastomosing tabulce, which simulate *' dissepiments." In the entire family of the Chcctetidce (assuming these in the meanwhile to be Actinozod) the " tabulae " are well developed; but there are no septa, and therefore no "dissepiments," unless the latter are represented by the tabulae. Lastly, in the Helioporidce it has been shown by Mr Moseley that the so-called septa are not homologous with the septa of the Zoantharia ; and it is therefore improbable that the well-developed tabulae of the former should be homologous with the " interseptal dissepiments " of the latter.

Whatever may be, however, the nature of the " tabulae " in the various groups of Actinoza which possess them, and whether or not they are always periodic partitions formed after the discharge of the ova (Verrill), or mere modifications of the interseptal dissepiments (Lindstrom), it is clear that they cannot be homologous with the apparently identical structures in certain other sections of the old group of the " Tabulata." Mr Moseley, for example, has shown that the Milleporce are truly Hydrozoa, and that their ova are therefore not produced within the visceral chambers. It is clear, therefore, that in these forms the " tabulae " cannot be modified " dissepiments," and still less partitions formed subsequent to the extrusion of the ova. It must also be admitted that any transverse plates which may be found to intersect the cells of undoubted Polyzoa (such as Heterodictya, Nich.) must be of a fundamentally different nature to the " tabulae " of either the "tabulate" Actinozoa or of the Millepores, though they may not be distinguishable from these in appearance.^

1 It follows from the above that if the name of " tabulse" be retained for the transverse partitions found in the visceral chamber of certain Actinozoa, it can hardly be said in any strict scientific sense that "tabulje" are present in certain Hydrozoa {^Milleporida) and certain Polyzoa {Hetcrodictya). The proper course,

With the abandonment of the "tabulae" as structures of classificatory significance, the '"Tadiilata" of Milne- Edwards and Haime must necessarily be broken up and undergo redistribution. It remains, however, for consideration, what groups are really included under the old name of ''Zoantkaria Tabulatal' and whether or not this name may still be retained, in a restricted sense, for any of the forms originally placed under it. By the investigations of Agassiz, Verrill, Lindstrom, Duncan, Moseley, Rominger, and others, we have been made acquainted with the true structure and relationships of several of the groups which constituted the old division of the Tabulata, and my own researches upon the varied and numerous Palaeozoic types have enabled me to throw some light upon the nature and position of some of the others. Our present knowledge is admittedly imperfect ; but it would appear that the division of the Zoantharia Tabtdata, as until very recently understood, comprises about twelve distinct groups of animals. Of these groups, the first two are not known (with any certainty, at any rate) to have had any Palaeozoic representatives, and I shall therefore say here what appears to me to be necessary concerning them ; while I shall merely summarise the characters of the remaining groups, all of which I shall have to treat of hereafter at greater length : —

I. MiLLEPORiD/E. — The corallum in this group is usually foliaceous, lobate, or sub-massive, and it is composed of an extremely porous coenenchyma, traversed in every direction by tubular canals, which freely communicate with one another, and which also open into the visceral chambers of the polypites themselves. The surface (fig. i, c) exhibits two sets of apertures, one large and the other small, the larger ones being much the fewest. The large openings (the true " calices ") are the mouths of tubes which are crossed by well-developed transverse partitions or "tabulae" (fig. i, b), the living animal inhabiting only the outermost of the chambers thus formed.

in fact, would be to give another name to the structures in the two latter groups which simulate the "tabular" oi' the first group.

CLASSIFJCA TION.

The smaller tubes are similarly "tabulate." No "septa" are present. The living- animal of Millepora was first examined by Professor Louis Agassiz, as the result of which he pronounced it to be a Hydrozoon, allied to Hydradinia ; but its anatomy was first thoroughly studied and worked out by Mr Moseley (Phil, Trans,, vol. clxvii. p. 117, 1877), who showed that it was in reality the type of a special group of Hydrozoa,

Fig. I. — A, Portion of a mass of Millepora alc/coniis, of the natural size; B, Portion of the same, cut open vertically to show the larger tabulate tubes (/, /), and the spongy coenosarcal skeleton (c, c), enlarged; C, Small portion of the surface, enlarged to show the larger and smaller openings (/', (f) inhabited by the different zooids, and the reticulated calcareous tissue of the skeleton ; D, Part of a polypite, enlarged, showing two whorls of knobbed tentacles. (A, B, and C are after Milne-Edwards and Haime ; D is afier Martin Duncan and Major-General Nelson.)

to which he gave the name of HydrocorallincE. According to the observations of this naturalist, the colony of Mtllcpora consists of two kinds of zooids, differing from one another in size, in structure, and in function. The larger zooids — the "gastrozooids " of Mr Moseley — occupy the larger tubes of the corallum, and have the form of short polypites, each of which possesses four tentacles, surrounding a central mouth, which opens into the gastric cavity of the zooid (fig, 2, a). Mixed with the "gastrozooids," or surrounding these in definite systems, are more numerous long and slender zooids — the " dactylozooids " of Mr Moseley — which carry numerous clavate tentacles (fig, 2,

TABULATE CORALS.

b), and are destitute of any mouth. The " dactylozooids " perform the functions of prehension for the colony, and supply food to the " gastrozooids," by which the work of digestion

Fir

. 2. — Enlarged view of a portion of the surface of a living colony of ]\Iilh'po)-n nodosa, showing the expanded zooids of a single system, a, Central "gastrozooid ;" /', One of the mouthless "dactylozooids." (After Moseley.)

and assimilation is carried on. The nutritive fluid thus elaborated Is distributed over the entire colony by means of branched coenosarcal canals, which communicate with the body-cavities of the zooids, and ramify in every direction through the spongy ccenenchyma.

Of the genera associated by Edwards and Halme with Millepora, Heliopora and its Palaeozoic and Secondary allies are now known to be referable to the Alcyonaria; Fistiilipora, M'Coy, belongs undoubtedly to the family of the Monticuliporidce ; and the Tertiary Axopora, with its fasciculate columella, is of uncertain affinities. Millepora itself Is only known as a Tertiary fossil, and as living ; but the Cretaceous genus PorosphcEra, Steinm., appears to be closely related to Millepora, and therefore also to belong to the HydrocorallincE.

II. PociLLOPORiD^. — The corallum (fig. 3) of Pocillopora, the type of this group. Is dendroid or foliaceous, composed of numerous tubular corallites, which are surrounded by an imper-

CLASS I PICA TION.

forate compact coenenchyma ; are provided with six, twelve, or twenty-four septa, sometimes obsolete ; and are intersected by complete transverse tabulae. A rudimentary columella is present. The animal of Pocillopora has been examined by Professor Verrill {loc. jam cit.), who describes the polypes as being " exsert in expansion, with a regular circle of twelve nearly equal, stout, tapering tentacles surrounding the circular disc ; and twelve internal, radiating, fleshy lamellee show through the disc. Thus they closely resemble the polypes of StylopJiora, Porites, and Madrepora, which are among the most typical of the true polypes. The existence of stellate cells

Fig. 3. — A, Portion of the corallum of Pocillopora aspera, var. lafa, Verrill, of the natural size ; B, Part of the surface of same enlarged ; c. Section of the corallites of the same, showing the columella, enlarged ; D, Vertical section of the same, enlarged, showing tabulce. (After Dana.) Recent.

with six or even twelve well -developed radiating septa in several species of Pocillopora {e.g., P. eloiigata, Dana, P. plicata, D., P. stellala, V.), should be sufficient evidence that such Corals have no Acalephian affinities whatever, even without the conclusive evidence derived from a study of the living polypes " (Amer. Journ. Sci. and Arts, ser. 3, vol. iii. p. 191).

It cannot be doubted, then, that Pocillopora, Lam., is a true Aporose Zoantharian, most nearly allied to the OcttlinidcE ; but there is some doubt as to the forms which should be associated with it, since in none of the allied types are we acquainted with the structure of the animal itself The corallum of Seriatopora, Lam., however, so closely resembles that of Pocillopora in its i6

TABULATE CORALS.

general structure, that this genus must ahnost certainly be placed alongside of the latter, even if not actually united with it, as proposed by Professor Martin Duncan. We may thus abolish the family SeriatoporidcB, of which Seriatopoi^a was the type. The genus Pocillopora is Recent and Kainozoic, and it is questionable if any fossil forms of Sci'iatopora are known. It may at any rate be taken as certain that the alleged forms of Seriatopora from the Palaeozoic deposits will be proved to have different affinities. The Palaeozoic genera Trackypora, Deiidropora, and Rhabdopora, usually associated with Seriatopora, Lam., are, again, truly Perforate Corals destitute of a coenenchyma, and belonging to the FavositidcE.

III. Favositid/E. — The corallum in this family is of very variable form, but is composed of polygonal or subcylindrical corallites, which are usually in close contact throughout their entire extent, and are furnished with well -developed walls. The walls are, however, perforated by a greater or smaller number of rounded apertures — the " mural pores " (fig. 4, b) — by which the visceral chambers of contiguous polypes are placed in direct communication. There is no true coenenchyma ; and the condition of the septa is extremely variable,

Fig. 4. — A, Portion of the corallum o{ Favosites favosa, of tlie natural size ; B, Portion of four corallites oi Fa7'osifes Gothlandica, enlart^ed, showing the talnilx* and the "mural pores."

these structures being sometimes obsolete (some forms of Trackypora^ &c.), sometimes in the form of marginal lamellae or ridges {IVyciopora, Nich.), and most commonly represented by vertically-disposed rows of spinules (most species of Favo-

CLASSII^ICATION. 17

sites). The tabulae are usually well developed and complete, but they are sometimes imperfect {Favositcs hemispherica, Yand. and Shum.)

After an extended study of the minute structure of the FavositidcE, I cannot doubt but that Professor Verrill and Dr Lindstrom are right in referring all the Corals usually included under this head to the Zoantharia Pei^foj^ata. I also fully recognise the many points of resemblance between the FavositidcB and the PoritidcB, but I am not prepared to follow the above-mentioned distingfuished authorities in reofarding the present group as a mere sub-family of the Poritid<2. On the contrary, I think that the group Favositidcs, as here understood, embraces a large number of types (mostly Palaeozoic), all of which are more or less allied to the PoritidcE, and some of which may perhaps be capable of final removal to the latter family, but which really represent a series of separate though allied groups. The reasons for this opinion will be stated at greater length hereafter. I need only say here that there is not the slightest ground, in my opinion, for regarding the Favositidcs as anything but true Actinosoa, or for removing them from the order of the Zoantharia. They are not connected with the Heliolitidcs by any links sufficiently close to lead us to suppose that they are Alcyonaria ; and the hypothesis of Dollfus (Comptes Rend,, t. Ixxx., 1875), that they are truly referable to the Polyzoa, hardly requires serious refutation.