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Show 1873.] DR. J. E. GRAY ON THE TRIONYCHlDcE. 69 families, like the bones on the hinder margin of the flexible edge of the shield, which is the peculiar character of the Indian genus Emyda. This bone is not to be observed in the young specimens of Tetrathyra and Baikiea. Synopsis of the Genera. * The dorsal disk of adult without any marginal bones on the hinder lateral edge. Africa. t The front and sides of alveolar edge of the lower jaw concave. BAIKIEA. Sternal callosities ? tt Alveolar edge of the lower jaw sharp in front, wider on the sides. T E T R A T H Y R A . Sternal callosities four-one pair anterior, and one pair lateral. C Y C L A N O S T E U S . Sternal callosities nine-two pairs anterior, one pair lateral, one pair posterior, and a single one central. ** The dorsal disk of adult with a regular series of internal marginal bones on the hinder lateral edge. India. E M Y D A . Sternal callosities seven-a pair anterior, lateral, and posterior, and a single one central. * The dorsal disk of adult without any marginal bones on the hinder lateral edge. Africa. t Front and sides of alveolar edge of lower jaw broad, slightly concave. BAIKIEA. Baikiea, Gray, Suppl. Cat. Sh. Rept. p. U 4 , fig. 39 (skull). The alveolar surface of the lower jaw flat, as wide in front as behind ; margin of the dorsal disk in the very young specimen without any front central bone, and without any bones behind. Hab. Africa. The adult skulls in the British Museum received from Dr. Baikie are about five inches long; they are somewhat like the skulls of Fordia africana, but are much blunter and rounded in front. 1. BAIKIEA ELEGANS. Cyclanosteus senegalensis (part), Gray, P. Z. S. 1864, p. 96, figs. 19-21 (skull only). Baikiea elegans, Gray, P. Z. S. 1869, p. 222, t. (young) ; Suppl. Cat. Sh. Rept. p. 116, fig. 39 (skull). Hab. Rivers of Western Africa, Dr. Baikie. The adult state of the shell or bones of this species is not known with certainty, and therefore we cannot describe the sternal callosities ; but I received some specimens of shells, with the jaws, which differed from the other specimens of Cyclanosteus in the relative size of the sternal callosities of this genus, and in their pro- |