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Show 70 DR. J. E. GRAY ON THE TRIONYCHlDcE. [Jail. 7, portional size as regards each other, which may be the shells of this genus. In the Supplement Cat. Sh. Rept. p. 113, I thought that the variety with additional sternal callosities (fig. 38) might ^ be a Baikiea ; but since that time the British Museum has obtained a specimen with its head and limbs, and the examination of the jaws shows it is a true Cyclanosteus, and that the adult state of Baikiea is still a desideratum. tt Alveolar edge of the lower jaw sharp in front, wider and concave on the sides. TETRATHYRA. Tetrathyra, Gray, P. Z. S. 1865, p. 332, fig. ; Suppl. Cat. Sh. Rept. p. 110, fig. 36 (sternum). Sternal callosities four, the lateral pair well developed, the anterior pair small and rounded, on the end of the front pair of bones. Hinder pair of sternal bones, and the odd anterior bone, small and without callosities. The flexible margin of the dorsal disk without any odd central bone in front, or any bones on the hinder margin. The skeleton of this animal is only known in the young state; perhaps the front odd bone and the posterior bone may have callosities in the adult state. The lower jaw is narrow and shelving internally in front, with a much wider concave alveolar edge on the side. 1. TETRATHYRA BAIKII. Tetrathyra baikii, Gray, P. Z. S. 1865, p. 324, fig. of sternum ; Ann. & Mag. N. H. 1865, xvi. p. 205, fig.; Suppl. Cat. Sh. Rept. p. 110, fig. 36 (sternum). Hab. Rivers of Western Africa, Niger? (Dr. Baikie). CYCLANOSTEUS Cyclanosteus, Gray, Suppl. Cat. Sh. Rept. p. Ill, fig. 37 (skull). Sternal callosities nine :-two pairs on the front pair of bones, the hinder pair generally the largest; a single semiovate callosity on the front central bone, generally longer than broad; one pair lateral, large, well-developed, deeply notched in the centre of the hinder edge; one pair posterior, on the separate simple posterior bones of the sternum : this pair is sometimes small and rounded, at others larger and ovate, placed obliquely as regards each other. The front part of the lower jaw is narrow and shelving, with a concave much wider alveolar edge on the side. The front bone of the dorsal disk short, broad, and transverse, differing in this respect from the much larger and longer first odd bone in Heptathyra. The front flexible margin of the dorsal disk with a well-developed central marginal bone. 1. CYCLANOSTEUS SENEGALENSIS. Cryptopus senegalensis, Dum. et Bibr., Erpel. Ge'n. p. 505. Emyda senegalensis, Gray, Cat. Tort. B. M . p. 47; Cat. Sh Rept. p. 64 ; P. Z. S. 1860, p. 316 (junior). |