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Pocillopora, so common a genus amongst the Indo-Pacific reefs, was found in the West-India Miocene, the Javan deposits, and at Turin and Dax. It is considered to be allied to Conites by Milne-Edwards, but Jules Haime doubted the Zoantharian characters of the last-named genus, which is Palæozoic. Seriatopora, a modern genus, does not appear to have been found fossil; but it is closely allied, according to the received opinion, with Rhabdopora, Dendropora, and Trachypora, all Palæozoic genera, the first being Carboniferous and the others Devonian. Millepora, the great reef-building genus of the West Indies, can be traced into the Lower Tertiaries, and is closely allied to the Heliopora already mentioned, and by structure to the Heliolites of the Palæozoic period.

Between the Lower Cretaceous reefs and the Paleozoic there were the Devonian, the Oolitic, the Lower Liassic, the Rhætic, and the St. Cassian and the Muschelkalk reefs, but not a trace of a tabulate coral has been recorded from them, in spite of the affinities of the modern and most ancient genera of the Devonian. Cyathophora has tabulæ, but its alliances are with the Astræidæ. On examining the lists published in my last Report, the absence of tabulate corals in the whole of the Mesozoic strata of Great Britain will be apparent, and I have not been able to distinguish any foreign forms belonging to that vast age (except our Holocystis elegans, Ed. and H.), of which notice will be taken in treating of the Rugosa and the species of Columnastræa.

Just as the Thecida, Favositidæ, and Halysitinæ formed the reef-builders of the tabulate fauna of the Palæozoic times, so Milleporida and Seriatoporida contribute to the recent reef-fauna; but these last genera had species in the Palæozoic fauna, so the break of the end of the Permian or Carboniferous periods was not complete so far as the Tabulata were concerned. The absence of them from the successive secondary reefs that have been examined by palæontologists has probably been produced by the destructive fossilization which is so common in existing reefs, and by the real absence of the forms from certain reef-areas of which there is an example (see West-Indian Fossil Corals,' Duncan).

The Tabulata were as abundant in the Paleozoic periods as during the Tertiary epochs, and the ancient and modern genera and species have certain characters which differentiate them more or less from all other coral forms. MM. Milne-Edwards and Jules Haime characterize the Tabulata as follows (Hist. Nat. des Corall. iii. p. 223):

The corallum is essentially composed of a well-developed mural system, and the visceral chambers are divided into a series of stages by transverse floors, which act as complete diaphragms.

The septal apparatus is rudimentary, and is either completely deficient or only represented by trabecula which do not extend far into the intertabular

spaces.

The lamellar diaphragms, floors, or tabulæ, which close the visceral chamber of the corallite at different heights, differ from the dissepiments of the Astræidæ by not depending in any manner upon the septa, by closing completely the space below, for they stretch uninterruptedly from side to side, instead of simply occupying the interseptal loculi.

The septal apparatus does not affect the Rugose type, but that characteristic of the Perforata and Aporosa. The forms classified under the section of the Tabulata are very numerous, and hence the importance of determining whether they can be undoubtedly allied with the rest of the Actinozoa.

Many years have elapsed since Agassiz expressed his opinion, founded upon direct observation, that the Millepore, an important genus of the Tabulata,

were not Actinozoa, but Hydrozoa, and lately he has reasserted this statement. If Millepora is one of the Hydrozoa, those tabulate forms which resemble it in structure, such as Heliolites, must reasonably be associated with it in classification. The importance, then, of determining this point is very great, and unfortunately it is accompanied by many difficulties. Before proceeding to criticise Agassiz's remarks, it is necessary to examine the nature of the structures of the genera associated with Millepora, or, in fact, to review the classification of the Tabulata, and to note their affinities with the other sections. Milne-Edwards and Jules Haime divide the Tabulata into four families:-Milleporida, Seriatoporidæ, Favositidæ, Thecida.

The principle upon which this classification is founded is philosophical and natural to a certain degree. The first two families have more or less cœnenchyma between the corallites, and the last two have little or none, the corallites being soldered together by their walls.

The genus Pocillopora unites the two divisions, for it belongs to the Favositidæ, and yet has a compact cœnenchyma on the surface of the corallum. The classificatory value of the presence of cœnenchyma in the whole of the Madreporaria may be estimated by examining the scheme of MM. MilneEdwards and Jules Haime.

When treating of the Madreporida (Hist. Nat. des Corall. vol. iii. p. 91), they subdivide them into Eupsamminæ without an independent cœnenchyma, Madreporina and Turbinarina with a very abundant cœnenchyma.

The Poritida they subdivide into the Poritina without conenchyma, and the Montiporine with an abundance of that structure in the spongy or alveolar form.

The Euphylliaceae (Ed. & H. op. cit. pp. 184 & 197) have such genera as Barysmilia and Dichocania, associated with Dendrogyra, Gyrosmilia, Pachygyra, Rhipidogyra, which have or have not much cœnenchyma.

The Stylinacea are divided into independent, "empâtées," and agglomerate. The independent genera have no cœnenchyma; the "empâtées" possess it in the extreme so as to merit the term peritheca.

The agglomerate have an excess of exotheca, but some genera are admitted which are united by their walls, and are therefore without exotheca or cœnenchyma. Thus Phylloconia has an exotheca quite cœnenchymatous, and Astrocenia has none. The corallites of Elasmocania have large mural expansions, and those of Aploconia are soldered by their walls. Heterocœnia and Pentaconia present the same anomalies.

The Astræinæ present such genera as Aphrastræa and Septastroa, the one with and the other without extramural tissue, and Heliastraa and Solenastraa with and Isastrea without the same structure.

It is then evident that the presence or absence of conenchyma had different significations in the estimation of the distinguished French zoophytologists. It is evident that the structure of the corallites of Isastrææ and their deficiency in cœnenchyma in comparison with the Heliastrææ and Solenastrææ cannot be of any very great organic significance; for the corallites of Heliastrææ occasionally grow so close together as to produce absorption of the exotheca and costa, and the same occurs in the Astroconiæ. The presence of exotheca, peritheca, and cœnenchyma (for they are grades of a particular structure) depends very much upon the habits of the corallum, and the notion of teleology can hardly be separated from the consideration of this presence and absence. Certainly to separate great groups by the presence or absence of cœnenchyma is not natural. It may be very useful to the classificatory student, because the limitation of forms is the prevailing want; but it is not

so to the biologist, for these mixed and unnatural limitations and separations only form gaps in his argument, which require bridging over.

The Favositidæ and Thecida, Palæozoic forms, may then be separated, for the purposes of classification, from the Milleporida and Seriatoporida, which are almost all post-Palæozoic; but this limitation is not to impede the plain course of the paleontologist, who studies from a biological point of view; nor is it to stand in the way of the assertion, that the break between the Palæozoic and younger Tabulata is almost nil.

The genus Millepora belongs to the Milleporida, and the cœnenchyma of its species is very abundant. It is of " a very irregular and spongy structure, rather than tubular" (Ed. & H.). The calices are of very different dimensions on the same corallum. There are no distinct septa, nor is there a columella. The tabulæ are horizontal. These are the diagnostics of the genus according to Milne-Edwards and Jules Hame. A careful examination of the calices of good specimens determines that the trabecula, of which the cœnenchyma is composed, often projects into them, in the position of septa; but there is nothing like the regular arrangement as seen in Heliopora, or in the Poritidæ of the Perforata. The cells of the cœnenchyma may occasionally be seen to open into the space above the last tabula.

The absence of septa and this relation of the conenchyma to the gastric space are most important. The tubular nature of much of the cœnenchyma is evident, and longitudinal sections of some size prove that the spongy nature of it is by no means constant nor uniform.

In Heliopora, belonging also to the Milleporidae, the cœnenchyma is very abundant, and covered here and there with rounded pores arranged more or less regularly and separated by papillose granules. These grains are the extremities of cylindrical "tigelles" which circumscribe the tubules, the calice of which is open at the surface. The calices are circular. The septa are slightly developed, and there are twelve of them. The tabulæ are well developed and horizontal (Ed. & H.). The nature of the conenchyma and the distinct septa distinguish this genus from the last. Both of the extinct species have a papillose or striated structure running over the cœnenchymal surface. In all the species the septa do not project far into the calice; but the amount of projection is not sufficient, as a structural peculiarity, in any case to determine more than a specific distinction. Hence MM. MilneEdwards and Jules Haime when they separate, in their scheme of the Milleporida, Millepora and Heliopora and other genera from Heliolites, Propora, and Lyellia, the particular Palæozoic genera, they can only be permitted to do so on the plea that the plan renders the genera readily distinguishable. The projection or non-projection is not sufficient to determine a generic difference.

Now Heliolites has a beautiful conenchyma, very geometric, and not irregular and spongy; its cellules are placed regularly and symmetrically. In most of the species the septa are distinct, and project far inwards, but in Heliolites Grayi they are almost rudimentary.

The genus Polytremacis links Heliolites and Heliopora together, for its cœnenchyma is that of the second, and the septa resemble those of the firstnamed genus. Polytremacis is not older than Heliopora in the secondary ages, and the septal distinction which cannot expel Heliolites Grayi from its genus, and which is improperly allowed to distinguish Polytremacis and Heliopora, and these and Heliolites, may well have been produced by variations in a succession of early secondary forms.

* Op. cit. p. 225.

The septal development of Heliolites is exaggerated in Propora, a genus from the Upper Silurian, and which perhaps lasted into the Carboniferous. The costa in this genus are well developed, but the cœnenchymal cells are less geometric than in Heliolites. The structural relations are of the closest, and the generic distinction is not of the usual generic value. Another Upper Silurian genus, Lyellia, represents these symmetrical Milleporida in America. The corallite walls are subcostulate and not so costulate as in Propora. The septa (12) are well developed, as in Heliolites and Propora and Heliopora, and the coenenchyma is perfectly vesicular-spongy, in fact, like Heliopora. Here, then, in the distant and British and Northern European Silurians, there were closely allied forms varying amongst themselves, but more than the secondary types, the variation having some sort of likeness in both instances. It is impossible not to acknowledge the genetic affinities of all these genera except Millepora, of which more will be said, or to hesitate to assert that there has never been a break in the Tabulata, and that the Recent and Palæozoic Heliopora and Heliolites are very closely allied, the one being the descendant of the other*. Axopora is a tertiary genus, and its immense columella, which fills up the corallite inferiorly and leaves but little room in the calice around it, of course prevents the tabulæ from reaching across the axial space. The tabulæ come in contact with but do not perforate the columella, so that this structure grows progressively without any reference to them; they do not form floors upon which a columella is developedt. There are no septa, and the cœnenchyma is reticulate in the extreme. No living analogue of this genus exists, and exception may be taken whether it be a true coral. It has no Paleozoic representatives.

Battersbyia is a very remarkable Paleozoic genus, and has been examined by met. MM. Milne-Edwards and Jules Haime § classify it with the Milleporida, but apparently only provisionally; but it will be noticed elsewhere. I have associated Battersbyia and Heterophyllia together as a new division of the Aporosa of the Astræidæ, under the name of the Palastræaces, which are noticed in the first part of this Report.

The Favositidæ are divided by MM. Milne-Edwards and Jules Haime into the following subfamilies: Favositinæ, Chætetinæ, Halysitinæ, Pocilloporinæ. All are presumed to present the following family characteristics: The corallum is formed essentially of the lamellar walls of the corallites, and possesses hardly any or no conenchyma. The visceral chambers are divided by tabulæ, which are numerous and well developed."

The subfamilies without any conenchyma, and those whose corallites form a massive corallum, are the Favositinæ and the Chætetinæ, and the genera whose corallites are not united on all sides the Halysitina. The Pocilloporinæ constitute the cœnenchymal subfamily. One of the great difficulties of the zoophytologist appears strongly enough whilst investigating these Tabulata, for the question constantly arises, and can only be answered very unsatisfactorily, are such and such forms really Actinozoa? are they not Polyzoa, Hydrozoa, or of some class which has become extinct, and which has no modern representatives?

Some genera are characterized by the absence of septa. Thus Chatetes has long basaltiform corallites, numerous tabulæ which do not correspond in their plane throughout the corallum, no septa, and the reproduction is fissiparous.

*See Huxley's Address, Geol. Soc. 1870.

+ Pal, Soc. Tertiary Corals, 3rd Series, P. M. Duncan, pl. vii. figs. 11–15.
§ Op. cit. p. 244.

Phil. Trans. 1867.

Keyserling considered the genus to belong to the Alcyonaria amongst the Actinozoa; but MM. Milne-Edwards and Jules Haime, considering the great analogy between Chatetes and Favosites, and particularly with Beaumontia, "où la présence de cloisons n'est pas contestable "*, determined its position to be amongst the true Tabulata.

The same authors now recognize the necessity of separating Chatetes from Monticulipora, and assert that the members of the last-named genus increase by gemmation.

The genus Dania differs from Chatetes in having the tabulæ on regular planes which traverse the whole corallum. This peculiarity is hardly of generic value.

Stellipora (Hall) is not generically different from Monticulipora, and the truth of this assertion can be estimated by comparing the diagnosis of the genera given by MM. Milne-Edwards and Jules Haime +.

The differentiation of Dekayia (Ed. & H.)‡ and of Labechia is also unsatisfactory, and their more or less mammillated cœnenchyma ranges them together by the side of Stellipora as subgenera of Monticulipora.

Now Jules Haime, when investigating the Oolitic Polyzoa, classified forms without septa and with tabulæ, like Chatetes or Monticulipora, as Polyzoa, and the beautiful Stellipora were especially included.

Now the question arises, are there any recent Polyzoa whose soft parts have been examined that have tabulæ? From our knowledge of the recent Polyzoa, it is unsafe to answer this in the affirmative. There is a freshwater species which is said to have tabulæ, but the assertion requires confirmation. The classification, then, of these forms amongst the Polyzoa must be deferred, and I propose to decide against it now.

Beaumontia, the genus noticed above, is distinguished by MM. MilneEdwards and Jules Haime § as follows:-" This genus is distinguished from all other Chætetinæ by the formation of its tabulæ, which are irregular or vesicular, and it thus resembles Michelenia, belonging to Favositinæ." The presence of septa belonging to three cycles is asserted by the same authors, and this fact must remove the genus quite out of the neighbourhood of septaless forms.

The genera of the Chatetina were formerly Chatetes, Monticulipora, Dania, Stellipora, Dekayia, Beaumontia, and Labechia. It has been shown that Stellipora, Dekayia, and Labechia are subgenera of Monticulipora, that Dania cannot be separated from Chatetes, and that Beaumontia has no correct affinity with the others, and that it belongs to another family. The genera should stand thus:

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But the subgeneric names should be dropped.

This result is interesting because it eliminates Beaumontia and makes a compact series, the affinities of which are not Polyzoan, but which may be Alcyonarian or Hydrozoan.

The long tabular or basaltiform corallites of Chatetes and its allied forms,

Op. cit. pp. 271.

+ Ibid. p. 283.

+ Op. cit. vol. iii. pp. 272, 281.

§ Op. cit. vol. iii. p. 282.

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