CORALS AND CORAL-ANIMALS. 189 



Gorgoniaceae towards the other racial groups of the Alcyonaria. The feature held in common 

 by the two groups compared, is that they are both distinguished for the secretion of an axial 

 skeleton or " sclerobase," usually of a dendritic or tree-like form, and of a distinctly horny 

 or chitinous consistence. Here, however, the parallel ends. This horny axial skeleton, or 

 corallum, is, in the case of the Antipatharia, of a denser consistence than that of the Gorgo- 

 niaceae, while its surface, in place of being smooth, is almost invariably minutely echinate, or 

 hispid. A more essential distinction obtains with respect to the morphological structure of the 

 associated polyps, which in both instances form, as it were, a living bark around the axial 

 sclerobase. In the Gorgoniaceae hereafter described, the tentacles of the polyps are invariably 

 eight, while among the Antipatharia the smaller number of six only is dominant, if not universal. 

 It is on account of this normally small number of the tentacles, and of the corresponding 

 mesenteries or sarcosepta, that the Antipatharia are placed in a separate order. 



The typical species of the Antipatharia, Antipathcs arborca, constitutes what is popularly- 

 known as black coral, and is an important article of commerce. The branching corallum in this 

 type attains to a height of from three to four feet, the main trunk and larger branches, in well- 

 matured specimens, measuring one or two inches in thickness. Its structure, as shown in 

 transverse section, consists of closely aggregated concentric layers of a dense, wood-like, 

 tissue of the colour of ebon}', but susceptible of a much higher polish. An important fishery 

 for this black coral was formerly conducted in the vicinity of Jeddah in the Red Sea, its 

 produce finding a ready sale in the Indian market, for the manufacture of charms and 

 amulets. This Red Sea fishery has within recent years become nearly exhausted. The 

 development of a new field for collection would be attended with considerable profit; and such 

 a field undoubtedly exists on the Queensland coast. Fine examples of an almost identical black 

 coral, Antipathcs abies, are commonly brought in to Thursday Island by the Torres Strait pearl- 

 shell divers ; and entire, or more or less fragmentary, specimens are abundantly washed up 

 on the reefs and foreshores, as far south as the Capricorn Islands. An illustration of the 

 Queensland black coral with its associated polyps is included in Fig. 2, 2a, and 2B of Chromo 

 plate No. XI. 



A second species of black coral, Cirrhipathcs sp. (? spiralis), which forms a more or less 

 spirally twisted or simple, straight, rod-like corallum, several feet in length, is not unfrequently 

 obtained by the pearl-shell divers in Torres Strait ; and Mr. Brook has identified a specimen 

 collected by Professor H addon in the same locality as the C. angiiina of Dana. 



ORDER v.— ALCYONARIA. 

 The order of the Alcyonaria, briefly defined on a previous page, includes a considerable 

 assemblage of polyp-animals, all of which are distinguished by the possession of eight tentacles, 

 never more and never less, which tentacles, with rare exceptions, are fringed or pinnate. 



