Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/416

Rh 38G CORALS septa, the latter being twelve in number. The septa are thus seen to be pseudo-septa, and they cannot be regarded as homologous with the septa of the Zoantharia sclerodcrmata. The ccenen- chymal tubes are occupied by sacs lined by the endoderm, which are closed externally but communicate freely with the somatic cavi ties of the polypes by means of transverse canals. Mr Mosely eu^ests, with great probability, that the sacs lining the ccenea- chymal tubes are really of the nature of aborted polypes. (A similar suggestion was put forth by the present writer with regard to the ccenenchymal tubuli of Heliolites and its allies, upon other grounds. Trans. Eoy. Soc. Edin. t vol. xxvii. p. 248.) 6 A, Small colony of HeUolitts megaftoma, M Coy, of the natural size. B, Small portion of the surface of the same, magnified, showing the calicos (a) and coenenchymal tubuli (6). C, Vertical section of the same, enlarged, showing the tabulate corallites and the tabulate tubes of the coBnenchyma, The investigations and discoveries of Mr Mosely with regard to Heliopora are of special interest, as settling the true position of a number of fossil corals, which had previously been placed in the Tabulate division of the Zoantharia sclerodermata, but which must now be referred to the Alcyonaria. The discovery, also, of tabuloe combined with a genuine sclerodermic corallum in an undoubted Alcyonarian further raises a question as to the true affinities not only of the Tabulata generally, but also of the Rugosa; whilst the discovery of septa which do not correspond with the mesenteries of the living animal will produce important results in the study of the fossil corals generally. Without entering into any of these questions here, there can be no doubt but that the extinct genus Heliolites and its allies are so closely related to Heliopora as to necessitate their being placed in the Alcyonaria as members of the family Hdioporidce. In the genus Heliolites there is a well- developed sclerodermic corallum, the corallites being tubular, regularly tabulate, and usually with well-developed septa, whilst the ccenenchyma is composed of tabulate, geometric tubuli, smaller than the corallites and without septa, In the genus Plasmopora the corallum is very similar to that of Heliolites, differing chiefly in the fact that the crenenchyma is more vesicular, and the tubuli are not so distinct. Propora, again, can hardly be separated from Plasmopora, its chief distinction being that the calices are exsert. Lyellia, also, is closely related to Heliolites. Polytrcmacis, also, differs from Heliolites chiefly in its granular surface, and it is hardly separable from Hcliopora except by the fact that its septa are more developed. Finally, there are various extinct genera, such as Fistulipora, Callopora, &c., which have very close relationships to Heliolites, though they are destitute of septa, and which very probably will have to be ultimately associated in the same group. With regard to the distribution in space of the Alcyonaria, it is sufficient to say that they are very widely spread over the globe, occurring in all seas from the warmest to the coldest, and at almost all depths. The Alcyonidce are for the most part inhabitants of shallow water, but the Pennatulidce are represented up to almost the greatest depths yet sounded by the dredge. The Gorgonidoe are principally shallow-water forms, and attain their maximum of development in the seas of the tropics, abounding on coral reefs, to the beauty of which they greatly contribute. The red coral of commerce (Corallium rubrum) is a Mediterranean species, and occurs principally at depths of from 5 to 6 fathoms, though extending its range up to 120 fathoms or more. It is very largely sought after, aud obtains a high price for ornamental purposes. The &quot; coral fishery &quot; is carried on by means of machines of different construction, which are dragged over the sea-bottom, and which usually injure more of the coral than they actually bring to the surface. Hence many valuable coral-beds have been completely exhausted, and the industry has no longer the importance that it formerly possessed. The &quot; Organ-pipe corals&quot; (Tiibipora) are confined to the warm seas of the &quot; coral-reef region &quot; and the genus Heliopora, the only living representative of the family HeUoporid&i is confined to the Pacific and Indian Oceans. As regards their distribution in time, none of the Alcyonaria, except the Hdioporidce, can be said to be known with certainty in deposits of Palaeozoic age. The genus Protovirgularia was founded by M Coy for the reception of a Silurian fossil which he believed to be allied to the living Virgularice, but it appears to be certainly not of this nature, and is probably a graptolite. The family of the Helioporidoe is well represented in the Palaeozoic period ; the genus Heliolites being Silurian aud Devonian, Propora and Li/Mia being Silurian, and Plasmopora Silurian and doubtfully Devonian. If Callopora and Fistulipora be referred to this group, then we may also consider that we have Carboniferous and Permian representatives of it. The genus Polytremacis, again, is confined to the Cretaceous period. The family of the Gorgonidce is not known to be represented with certainty earlier than the Eocene Tertiary, two genera (Hopsea and Webster ia) being found in the London clay. The genus Corallium has been doubtfully quoted from the Upper Oolites and Upper Cretaceous, and undoubtedly occurs as early as the Miocene. The Miocene deposits have also yielded species of Isis, Gorgonia, Gorgonella, and Melithcea. The family of the Pennatulidce is not represented earlier than the latest Secondary or the earlier Tertiary deposits. The genus Pavonaria is said to occur in the Pisolitic Limestone of France, whilst Grapliu- laria (and perhaps Virgidaria) is found in the Eocene. The Miocene Tertiary has also yielded species of Virgularia, Graphidaria, and C celograpJiula. The family of the Tubiporidoe has not been recognized at all in a fossil con dition. Lastly, the past existence of the Alcyonidce has only been recognized with any certainty in the Pliocene deposits, the P^ed and White Crags having yielded a species of Alcyonium. BIBLIOGRAPHY. Amongst the more important works and memoirs which may be consulted by the student of recent and fossil corals may be mentioned the following: Agassiz, Louis, Contributions to the Natural History of the United States, vols. iii. and iv., on&quot; Acalephs ;&quot; De Blainville, Manuel d 1 Actinologie et de Zoophytology, 1837 ; Bronn, Die Klassen und Ordnungen dcs ThierreicWs (Strahlcnthiere), vol. ii. parts 1-6, 1859-60; Cuvier, Regne Animal, 3ded. vol. iii., &quot;Zoophytes;&quot; Dana, Rep. of Wilkess Expl., Exped. &quot;Zoophytes, 1848 ; also Corals and Coral Islands, 1872 ; Edwards and Haime, Histoire Naturclle dcs Coralliaires, ou Polypes proprement dits, 1857-60 ; also by the same, &quot;Eecherches sur la Structure et Classification des Polypiers recents et fossiles, in Ann. Sc. Nat., 1848-52 ; Ehrenberg, Beitrdge zur Physiologischen Kcnntniss der Corallenthiere iin Allgemeinen, und besonders dcs Rothcn Mccres, Berl. 1834 ; Ellis, Essay towards a Natural History of the Corallines, &c., 1755; Ellis and Solander, The Natural History of many Curious and Uncommon Zoophytes, 1786; Gosse, Actinologia Britannica, A History of the British Sea- Anemones and Madrepores, 1860 ; Greene, Manual of the Ccelcnterata, 1861 ; Johnston, History of British Zoophytes, 2d ed. 1847 ; Kolliker, Icones Histiologies, Abth. ii., die Bindesubstanz dcr Ccelcntcraten, 1865; Lacaze-Duthiers, Histoire Naturelle du Corail, also &quot;Developpment Jes Coralliaires,&quot; in Archives de Zobl. Experimental, 1872-73 ; Lamarck, Hist. Nat. dcs Animaux sans Vert., 2d ed., 1836-39; Lamouroux, Exposition Methodique des genres de I ordre des Polypiers, 1821 ; also Histoire des Polypiers JlcxibUs, 1816 ; Leuckart, Uebcr die MorpJwlogie dcr wirbellosen Thiere, 1848 ; Pourtales, &quot;Deep-Sea Corals,&quot; No. 4 of the Ulust. Catalogue of the Mus. of Comp. Zoology, 1871 ; Quoy and Gaimard, Voyage de V Astrolabe, also Voyage do rUranie; Eapp, Ucber die Polypen im Allgemeinen und die