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represented at Brockenhurst. In the great reefs of the Castel-Gomberto district there are the remains of a larger coral-fauna than that which now exists in the Caribbean Sea ; and although a profound Flysch exists between them and the reefs in the Oberburg district, indicating great oscillations of the area and vast changes in the life of the time, still the genera which contribute so largely to the formation of modern reefs are found represented in abundance in the lowest reefs, which clearly belong to the Nummulitic period.
Our Eocene corals and those found at Brockenhurst are the stunted offshoots of the faunas which flourished at Oberburg and in the Vicentine, but nevertheless some of their species are closely allied to those of much later geological date.
Without the assistance of the labours of Reuss and D'Achiardi zoophytologists could not have imagined that the well-known coral-faunas of the Hala Mountains of Sindh, of the Nummulitic deposits of the Maritime Alps and Switzerland, and of the London and Paris basins were but fractions of a fauna which was probably richer in species than any modern coral tract; and this welcome aid proves the impropriety of neglecting foreign palæontology, even when writing reports like the present, and which treat of the productions of the rocks of a small area. The impossibility of comparing with any satisfaction the Nummulitic coral-fauna and that of the Upper Chalk is obvious; because the Nummulitic fauna, so far as it is known to us, was either a reef or a comparatively shallow-water one, whilst the corals of the Upper Chalk were dwellers in a deep sea, where reef species cannot and could not exist. We must seek to compare the Upper Cretaceous corals with the deep-sea forms of the Nummulitic, but unfortunately they are not yet found*.
The Lower Cretaceous corals of Great Britain were the contemporaries of the reef-builders of the Gosau and equivalent formations, and thus deep-sea and reef species were contemporaneous, as they are at the present time, but they were separated by wide distances. The comparison of the reef-fauna and that of the deep sea is in this instance as futile as it would be at the present time; but we may compare the reef-fauna of Gosau with that of the Nummulitic, Oligocene, Miocene, and existing reefs, and not without benefit and good results, for there are persistent species which unite the whole together.
A comparison may also be instituted between the deep-sea coral-faunas of the Chalk and those which flourished at corresponding depths in the succeeding geological epochs. Thus, thanks to Messrs. Wyville Thomson, Carpenter, and Jeffreys, I have been able to assert the extraordinary homologies between the deep-sea Cretaceous corals and those which now exist to the west of these islands. These results are being published by the Zoological Society. The present arrangement of coral genera in and about reefs was foreshadowed as early as the Eocene, and such assemblages of genera existed in those old reefs as would characterize the coral life of atolls in the Caribbean Sea and in the raised reefs of the Pacific Ocean. The genera Madrepora, Alveopora, Porites, Heliastrea, and Millepora were represented in the Oberburg, and their species constitute the bulk of existing reefs. It is important to be thus able, from the labours of MM. Milne-Edwards, J. Haime, and Reuss, to determine the existence of Perforate and Tabulate corals in the earliest tertiaries, for interesting links are thus offered to the palæontologist by which the older and the newer faunas are connected. Such researches diminish the importance of the break between the early Tertiary fauna and the present, and also, to a
* See P. M. Duncan on a new Coral from the Crag, and on the persistence of Cretaceous types in the deep sea (Quart. Journ. Geol. Soc. sxvii. pp. 369 & 434).
certain extent, that between the Palæozoic and recent faunas. Thus the finding of species of the great Perforate genus Madrepora in the Oberburg carries the genus a step further back than their discovery in the Oligocene of Brockenhurst, and when taken into consideration with the presence of the Stephanophyllia, a perforate simple coral, in the Crag, Eocene, and Lower Cretaceous deposits, and with Actinacis, a highly developed compound form, in the Lower Cretaceous strata of Gosau, the immense break between the next form of the family and the existing is materially diminished. The next form is not met with until the Carboniferous deposits of Indiana are reached in a downward course; and we owe to the late Jules Haime the knowledge of the structures of Palæacis cuneiformis, Haime, MS., from Spurgeon Hill, Indiana. It is indeed remarkable that the vast coralliferous strata which intervene betweon the Carboniferous and the Lower Chalk should not present a satisfactory proof of the existence of those members of the existing great reef-building family. There is a curious fact which may be taken for what it is worth in considering the absence of genera which have been represented in some ancient deposits and which have not been found in intermediate strata. Thus the existing West-India reefs contain abundance of the species of the genus Madrepora and Millepora ; indeed they, with the forms of Porites, constitute the bulk of the formations. Now, although Porites is common in the Miocene reefs of the area, the others are very rare, for the coral structures were principally composed of tabulate forms and Heliastræans. Yet we know that before the Miocene reefs flourished, Madreporæ and Milleporæ were common enough; they were living all the while in other coral tracts. But the break between the Palæozoic and the Lower Cretaceous forms cannot be bridged over without investigating the value of the classification which separates the most closely allied subfamily of the Perforata, although the Perforata are found in the Great Oolite.
II. The Perforata characterized by a porous cænenchyma and other tissues present many modifications of their hard parts. Some approach the Aporosa, and others would hardly be considered corals by the uninitiated on account of the sponge-like reticulations of the skeleton. The genus Vadrepora is defined as follows by MM. Milne-Edwards and Jules Haime :
The corallum is compound and increases by budding. The cænenchyma is abundant, spongy, reticulate, slightly or not at all distinguishable from the walls, which are very porous. The visceral chambers are subdivided by two principal septa, which meet by their inner margins, and are more developed than the others.
The septa, especially the two largest, although perforated, are continuous, and very often lamellar.
MM. Milne-Edwards and Jules Haime distinguish the Poritidæ in the following manner :
The corallum is compound, and entirely formed of a reticulate cænenchyma, which is formed of trabeculæ and is porous. The corallites are fused together by their walls, or by an intermediate cænenchyma, and they multiply by budding, which is usually extracalicular and submarginal.
The septal apparatus is always more or less distinct, but never completely lamellar, and is formed by a series of trabeculæ, which constitute by their union a sort of lattice-work. The walls present the same structure as the septa. The visceral chambers sometimes have rudimentary disse piments, but are nerer divided by tabulæ.
This family is divided into two subfamilies—
It will be notieed, when specimens of Montiporinæ and Madreporæ are compared, that the distinction is in the absence of the two large and not very perforate septa in the case of the first-mentioned group, and it is clear that the excessively trabecular character of its septa, conenchyma, and walls is characteristic. Moreover the Montiporinæ are recent forms.
The genus Litharca amongst the Poritinæ approaches Madrepora, however, and its septa are often so lamellar that they resemble those of some Heliastræans amongst the Aporosa. Here the distinction between the forms becomes limited. The two great septa are not extended to the median line in Litharæa, and there is scanty cænenchyma, but still there is some. The columella of Litharca is simply formed by the union of trabeculæ from the septal ends.
Now Protarca vetusta, Hall, and Protarca Verneuili, Ed. & H., Lower Silurian corals from Ohio, only differ from the species of Litharæa by having more aporose septa and some cænenchymal protuberances*. It is necessary, however, on account of the comparatively late appearance (so far as our investigations has as yet gone) of Madrepora and Litharca, whilst admitting the extraordinary relation of the last-named genus to Protarcea, to examine another of the Jurassic Perforata.
The genus Microsolena of the Poritinæ carries the excessively trabecular type of the Poritinæ as far back as the Great Oolite ; it is of course one of the extreme forms, and most remote from Madrepora. It has more or less confluent septa, and nothing like the styliform columella of Protaræa. Thus Palæacis, a form of the Madreporinæ, and Protarca, a type of the Poritinæ, are still unsatisfactorily disconnected by intermediate species with their allies in the secondary rocks. But, on the other hand, it is something to be able to show an anatomical connexion between the Protarceve of the Lower Silurian and the Microsolence of the Jurassic and of the Litharææ of the Nummulitic rocks, and between Palæacis and the Turbinarians of the group Madrepora, of which Actinacis is the oldest (Lower Chalk)t. It shows that the reticulate or perforate corals existed amongst the first known coralliferous rocks, that the scheme of their organization has been perpetuated to the present day through many kinds of variations, but with a great break, which is owing to the imperfection of the geological record.
III. The Tabulata, which form such large portions of many modern reefs, were, as has been already noticed, in existence during the Miocene, the Oligocenes, and the Eocenell. They were, of course, not found amongst the deep-sea deposits of the Cretaceous period, such, for instance, as our White Chalk; but Reuss found the genera in the reefs of Gosau.
Gosau. Heliopora Partschi, Reuss, sp.; H. macrostoma, Reuss, sp. ; Polytremacis Blainvilleana; P. bulbosa, d'Orb.: these are not uncommon in the reefs which were in relation with the Hippurites, and the last coral genus lived during the Eocene. Reuss established a genus in 1854 for some compound, massive corals, with prismatic corallites with thick imperforate walls. The calices are without radiating septa and have no columellæ. The tabulæ are very irregular, some being complete and others uniting obliquely with their neighbours. The septa are represented by trabeculæ. This Lower Cretaceous genus he named Stylophyllum, and will be considered further on.
* See Hist. Nat. des Corall. vol. iii. p. 185.
See Duncan, West-Indian Fossil Corals (Q.J. Geol. Soc.); Reuss, Corals of Java, &c.
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 Coenites 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 Palæozoic 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 Columnastroa.
Just as the Thecidæ, Favositidæ, and Halysitinæ formed the reef-builders of the tabulate fauna of the Palæozoic times, so Milleporidæ and Seriatoporidæ 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 (sec • West-Indian Fossil Corals,' Duncan).
The Tabulata were as abundant in the Palæozoic 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 trabeculæ 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 A porosa. 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 :—Milleporidæ, Seriatoporidæ, Favositidæ, Thecidæ.
The principle upon which this classification is founded is philosophical and natural to a certain degree. The first two families have more or less cænenchyma 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 conenchyma on the surface of the corallum.
The classificatory value of the presence of cænenchyma in the whole of the Madreporaria may be estimated by examining the scheme of MM. MilneEdwards and Jules Haime.
When treating of the Madreporidæ (Hist. Nat. des Corall. vol. iii. p. 91), they subdivide them into Eupsamminæ without an independent conenchyma, Madreporina and Turbinarinæ with a very abundant cænenchyma.
The Poritidæ they subdivide into the Poritinæ without cænenchyma, and the Montiporinæ with an abundance of that structure in the spongy or alveolar form.
The Euphylliaceæ (Ed. & H. op. cit. pp. 184 & 197) have such genera as Barysmilia and Dichocenia, associated with Dendrogyra, Gyrosmilia, Puchygyra, Rhipidogyra, which have or have not much cænenchyma.
The Stylinaceæ are divided into independent, “empâtées,” and agglomerate. The independent genera have no cænenchyma; 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 conenchyma. Thus Phylloconia has an exotheca quite conenchymatous, and Astrocenia has none. The corallites of Elasmocoenia have large mural expansions, and those of Aplocoenia are soldered by their walls. Heterocoenia and Pentaccenia present the same anomalies.
The Astræinæ present such genera as Aphrastræa and Septastræa, the one with and the other without extramural tissue, and Heliastrcea and Solenastræa with and Isastræa without the same structure.
It is then evident that the presence or absence of cænenchyma 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 cænenchyma in comparison with the Heliastrææ and Solenastrææ cannot be of any very great organic significance ; for the corallites of Heliastræte occasionally grow so close together as to produce absorption of the exotheca and costä, and the same occurs in the Astrocæniæ.
The presence of exotheca, peritheca, and conenchyma (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 conenchyma 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