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Show 1899.] ASTRcEID CORALS FROM THE SOUTH PACIFIC. 751 Genus ORBICELLA. Orbicella, Dana, Zooph. p. 205 (1848). Heliastrcea, Milne-Edwards & Haime, Cor. ii. p. 457 (1857). Heliastrcea, Duncan, Rev. Madrep., Journ. Linn. Soc, Zool. xviii. p. 104 (1885). Plesiastrcea, Milne-Edwards & Haime, Compt. rend, de l'Acad. des Sc. xxvii. p. 494 (1848), and Cor. ii. p. 489 (1857). Plesiastrcea, Duncan, Rev. Madrep., Journ. Linn. Soc, Zool. xviii. p. 107 (1885). L,eptastrcea, Milne-Edwards & Haime, Compt. rend, de l'Acad. des Sc. xxvii. p. 494 (1848), and Cor. ii. p. 493 (1857). Leptastrcea, Duncan, Rev. Madrep., Journ. Linn. Soc, Zool. xviii. p. 119 (1885). Orbicella and Leptastrcea, Klunzinger, Die Korall. des R. Meeres, iii. pp. 43-50 (1879). There are in my collection 20 specimens of this genus, in addition to which I have examined a very large number of colonies in the British and Cambridge Museums. The genus Plesiastrcea was separated from Heliastrcea by Milne- Edwards and Haime in 1848, and stated to have well-developed pali before all the cycles of septa except the last, while the pali in Heliastrcea are absent or rudimentary. In Heliastrcea acropora the pali are exceedingly well-developed before all the cycles of septa except the last; while in Plesiastrcea versipora the pali, although generally very distinct, are in some calices not recognizable. Again, these two genera are stated to have their whole septal edges toothed, while Leptastrcea has the upper edges of its septa entire and the lower edges toothed. This also is rather a question of degree, for in Leptastrcea solidior, while the upper edges are generally almost entire, in some calices they are finely and in others very markedly toothed. One of my specimens, too, of Orbicella (Heliastrcea) heliopora presents calices which, examined separately as to the above characteristics, would be placed in all the three so-called genera. Indeed, any large colony of almost any species of these genera has calices intermediate between those of the other two genera. Further, all these three genera have the same method of budding and plan of structure ; and indeed, from the study of the hard parts alone, there is no valid reason to separate them. For the genus I have, following Klunzinger, employed the term Orbicella, as it has clearly the priority, being first used by Dana for a subgenus of Astrcea. The genus Orbicella would then be characterized as follows:- Corallites forming massive and incrusting colonies, sometimes growing out into lobes, but usually forming rounded masses, covered below by a distinct epitheca. Calices generally completely separate, with the edges more or less prominent, often elevated. Corallites joined together by exotheca only, the costae never being continuous between calices, except where a young polyp has recently been budded off. Calices usually deep and closed in |