Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/410

380 CORALS Protoscns, Dimorphoscris, Oroscris, Anobacia, Gcnabacia, &c. In the Cretaceous period the proportions of the different families of the Aporosa are much the same as in the Oolitic. The Astrccidce are still by far the most numerous, the principal Cretaceous genera being Thamnastrcca, Synastrcea, Goniastrcea, Isastrcca, Heliastrcca, Cyphastrcea, Barysmilia, Trochosmilia, Placosmilia, Parasmilia, Pcplosmilia, Diplodenium, Phylloccsnia, Cryptoccenia, Astro ccenia, Stylocxnia, Centroccenia, Pleurocora. Cladocora, Hydno- plwra, Caryopliyllia, Brachyphyllia, Favia, Cyathophora, Mean- drina, Latimeaiulra, Diploria, Lcptoria, Stdloria, Rhipidogyra, Eugyra, Pachygyra, Montlivaltia, PJiizangia, &c. The Turbinolidce are represented by species of Trochocyalhus, Leptocyathus, Bradty- cyathus, Cydocyathus, Smilotrochus, Stylotrochus, Onchotrochus, &c. ; and the Pseudoturbinolidce by the genus Dasmia. Amongst the Oculinidce we meet with such genera as Synhdia and Diblasus; and the family of the Fimyidce is well represented by species of Cydolites, Micrabacia, Cydoscris, Podoseris, Cyathoscris, Trocho- seris, Oroscris, and Turbinoscris. The Cretaceous corals are not separated from those of the Eocene period by any break similar in extent to that which separates the coral-fauna of the later Palaeozoic rocks from that of the younger Mcsozoic ; but there is nevertheless a considerable difference observable. The Astrccidce are no longer so abundant, and are represented by genera such as Solenastrcea, Astrcca, Hcliastrcea, Montlivaltia, Stephanomnia, Phylloccenia, Astroccenia, Styloccenia, Parasmilia, Calosmilia, Cylicosmilia, Rhizangia, Dasyphyllia, Circophyllia, Latimeandra, Hydnophora, &e. The Turbinolidce are greatly developed, and are represented by numerous genera, such as Turbinolia, Trocho- cyathus, Lcptocyathus, Paracyathus, Flabdlum, Platytrochus, Discotrochus, Sphenotrochus, &c. The Pseudoturbinolidce are repre sented by the genus Dasmia, which dies out here. Amongst the Oculinidce, we meet with the genus Oculina itself, along with species of Diplokelia, Stylophora, &c. Lastly, the Fttngidce are represented by forms such as Cyathoseris, Trochoseris, and Cydo lites. In deposits of Miocene age, the Astrccidce are represented by the genera Astrcea, Prionastrcea, Plesiastrcca, Solenastrcea, Septa- strcea, Astroccenia, Caryophyllia, LitJwphyllia, Montlivaltia, Hydnophora, Cladocora, Trochosmilia, Diploctenium, Rhizangia, Phyllangia, Cryptangia, Cladangia, &c. Amongst the Miocene Turbinolidce are the genera Trochocyatlius, Ddtocyafhus, Acantho- cyathus, Sphenotrochus, Ceratolrochus, Desmophyllum, and Fla- bdlum ; whilst the Oculinidce are represented by species of Oculina, DiploJielia, Astrohdia, and Stylophora, and for the first time Pocillopora. The Fungidce, finally, are poorly represented by the genus Cydolilcs. The Pliocene deposits have hitherto yielded a small number of corals, belonging to solitary forms, the Astrccidce being represented by Caryopliyllia, Cryptangia, Ac., the Oculinidce by Oculina itself, and the Turbinolidce by forms such as Flabellum, Sphenotrochus, and Paracyathus. The geological history of the great group of the Perforata is shorter and less perfectly known than that of the Aporosa. Leav ing out of sight forms of uncertain affinities, the Perforata are but represented in the great pile of Palaeozoic deposits by some two or three genera, and they are absent or very poorly represented in all the lower Mesozoic sediments. In the Cretaceous period they for the first time begin to be more abundant, though still sparsely developed, and it is not till the commencement of the Tertiary period that this group assumes anything like its present pro portions. In the vast series of Silurian deposits the Perforate corals are only represented by two undoubted genera, namely the Protaram of the Lower Silurian, which belongs to the Poritidcc, and is nearly allied to the genus Litharcca, and the sin gular Calostylis of the Upper Silurian. The Lower Silurian genus Columhopora may perhaps be referred to the Madreporidce, and if the Favositidce were ultimately referred to the same family, then we should have to admit a very considerable development of the Perforata in Upper Silurian times. In the succeeding period of the Devonian, rich as it is in corals, no certain representative of the Perforata is known. The genus Pleurodictyum has been referred here, but is apparently founded upon casts of Favosites. In the great coralliferous deposits of the Carboniferous, again, no represen tative of the group is known, save the single genus Palccacis, which appears to be a Madreporacean. In the Permian rocks, the Trias, and the Lias, no single example of a Perforate coral has hitherto been brought to light, and the group is represented in the Oolitic series by the single genus Microsolena, an aberrant member of the Poritidce. In the Cretaceous series the Perforate corals are represented by members of all the existing families, Stejmano- phyllia amongst the Eupsammidce, Porites amongst the Poritidcc, and Actinacis amongst the Madreporidce. In the Eocene rocks a much more striking development of the Perforata takes place. The Eupsammida are now represented by Eupsammia, Slereo- paimmia, Lobopsammia, Endopachys, Balanophyllia, Stephano- phylha, Dendrophyllia, &c. The Madreporidce appear under such forms 03 Madrepora, Alvcopora, Astrceopora, and Dendracis ; and the Poritidcc are represented by such genera as Porites and Lith arcca. In the Miocene period the Eupsammidce are represented by Balanophyllia, Stcphanophyllia, Dendrophyllia, Eupsammia, &c., the Madreporidce by Madrepora and Turbinaria, and the Poritidce by Porites and Jihodarcea. In the Pliocene period the Perforata appear to be principally represented by Eupsammidce, such as Balanophyllia, Stephanophyllia, Dendropliyllia, and C ceno- psammia. In discussing the geological distribution of the Tabulate Corals, it will be convenient to consider the group as a merely provisional as semblage of forms, which cannot at present be finally systematized. The genus Ildiopora and its allies Hdiolitcs, Plasmopora, &c., have been shown to be Alcyonaria, and will be considered under that head. Here, therefore, the order Tabulata will be taken as tempo rarily including the groups of the Milleporidce (Millepora, Axopora), the Thecidce (Thecia), the Favositidce (Favosites and its allies), the Chcetetidce (Ckcetetes and its allies), and the Halysitidce (Haly sites, Syringopora, &c. ) Accepting the order in this provisional aspect, it will be found that the Tabulata are mainly, indeed almost exclu sively, confined to the Paleozoic period. The Milleporidac,, how ever, belong to the Tertiary and recent periods ; Koninckia is Cretaceous ; whilst Michelinia and some of the Chcetetidce have been stated to occur in the Oolitic series, though this determination is not free from doubt. The family of the Thecidce, including the single genus T/iecia, is exclusively Upper Silurian. Amongst the Favositidce, the type-genus Favosites is Silurian, Devonian, and Carboniferous, attaining its maximum of development in the Devo nian ; Emmonsia has nearly the same range as Favosites ; Miche linia is found in the Devonian and Carboniferous, and is doubtfully quoted from the Oolites ; Striatopora belongs to the Upper Silurian and Devonian ; Alveolites is abundant in the Silurian and Devonian, and disappears in the Carboniferous ; Rxmcria is Devonian, and Koninckia is only known from the White Chalk. Of the Chcetetidce, Ckcetetes, Monticulipora, and Stenopora are three imperfectly sepa rated and closely allied groups, which are represented, collectively orseparately, in all the Palseozoic formations from the Lower Silurian to the Permian, inclusive ; and forms very similar, if not identical, (Heteropora, Neuropora) occur in deposits of Mesozoic age. The genera Dania and Constcllaria are closely allied to the preceding, and are Silurian. Labechia may be temporarily placed here also, and is likewise Silurian. Fistulipora and Callopora are nearly related to the preceding and to one another (if not identical), and they range from the Silurian to the Carboniferous. Lastly, Beaumontia is Carboniferous. Amongst the Halysitidce, the type-genus Haly- sites is Silurian ; Syringopora ranges from the Silurian to the Car boniferous, attaining its maximum in the Devonian ; whilst the singular genus Fletcheria, though typically Silurian, is said to bo represented by a species in the Trias (Muschelkalk). Lastly, the aberrant family of the Millcporidce does not seem to have come into existence till the Eocene Tertiary, where it is represented by the genus Millcpora. The remarkable genns Axopora also dates its fii st appearance from the Eocene. There remain some other so-called Tabulate corals which have not been noticed in the above summary, but they are not of sufficient importance to require special mention. The small group of the Tiibulosa is confined exclusively to the Paleo zoic period. The type-genus Aulopora is found in the Lower and Upper Silurian, the Devonian, and the Carboniferous, attaining its maximum in the Devonian. The genus Pyrgia is only known as occurring in the Carboniferous rocks. Regarding the geological history of the Zoantharia sderodermata in a summary form, it will be seen that the Palaeozoic period is characterized by the exclusive possession of the 2 ubulosa, the great development of the Tabulata, and the very small number of Aporosa and Perforata, the place of these latter groups being takenby the Tabulate and Rugose corals. The Mesozoic period is characterized by the great development of the Aporosa, and, towards its close, of the Perforata, though in a less degree ; whilst the Tubulosa are wholly gone, and the Tabulata, along with the Rugose corals, have very nearly disappeared. Finally, the Kainozoic period is charac terized by the greatly increased development of the Perforata, the Aporosa being proportionately diminished, though still remaining in great force, and the great recent group of the Millepores (Tabulata?) now for the first time making its appearance. ORDER II. RUGOSA. The members of this order agree with the Zoantharia sderodermata in possessing a well-developed sclerodermic corailum, with a true theca, and generally presenting both tabulae and septa combined. The septa, however, are generally (though apparently not always) some multiple of four, and there is commonly a single predominant septum, or a vacant space (fossula) representing such a septum. Some of the Jtngosa are simple, others are compound,

but the latter are destitute of a true ccenenchyma.