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Show 187L] MR. W. S. KENT ON NEW MADREPORES. 279 whether the characters given may prove sufficient for the recognition of two distinct genera on other species becoming known. A. oculata (Ehr.) was the single form referred to the genus Allopora by Milne-Edwards in his work just quoted. Recently Count de Pourtales has discovered a second species, off the coast of Florida, which he describes in the Bulletin of the Museum of Comparative Zoology, Cambridge, U. S. for 1868, under the name of Allopora miniatu; and my examination of the collection in the British Museum has resulted in m y detecting three other distinct and undescribed species, undoubtedly referable to this same genus. The mass of evidence now accumulated demonstrates that Allopora and Stylaster constitute two natural and easily defined genera. The character of the presence or absence of ampullae, however, as shown in the following description of A. explanata, is not trustworthy even for the purpose of making specific distinctions. The whole and great difference must be based on their widely separated mode of development or gemmation, which is easily recognized on reference to figs. 1 a and 2a of Pl. XXV., and fig. 1 a oi Pl. XXIV. accompanying this communication. In Allopora the corallum is aborescent, more or less massive, and has the calices distributed irregularly throughout its surface, this last character being likewise applicable to the mode of their first appearance at the extremities of the branchlets. In Stylaster the corallum is wanting in that massive and robust mode of growth characteristic of Allopora, and the gemmation is invariably alternate distal, as in Amphihelia, Lophohelia, and other Oculinidae, and which, though sometimes disguised by the increase of the ccenenchyma in the basal portions of the corallum, is always apparent at the growing termination. Even in the former parts the peculiar primary mode of gemmation is betrayed by the more or less regular disposition of the calices in a linear series on either side, rendered sessile by the outgrowth of the ccenenchyina. This distinction makes easy our appreciation of the, at first sight, somewhat obscure characters of the form referred to the genus Allopora by Dr. Duncan, to be presently referred to. In Allopora this latero-linear distribution of the calices is altogether absent. ALLOPORA NOBILIS, n. sp. Corallum arborescent, the main stem and branches very massive, slightly flattened; the branchlets subflabellate, thick, terminating obtusely. Surface of the ccenenchyma smooth to the unassisted eye, but presenting a delicate shagreened appearance when examined with the pocket-lens. Calices densely distributed throughout the surface of the corallum, slightly prominent; very minute, scarcely exceeding one-third of a line in diameter. Septa varying in number from three to seven, more usually six; their inner edges joining laterally a little below the entrance to the calice, and forming minute pit-like interseptal chambers, within each of which, as in Stylaster erubescens (Pourtales), is enclosed a vertical fringe of small points resembling hairs. Columella deeply immersed, cylindrical, its apex |