1873.] DR. J. E. GRAY ON THE TRIONYCHID.dE. C9 



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 jaio concave. 

 Baikiea. Sternal callosities ? 



tt Alveolar edge of the lower jaw sharp in front, ivider on the 



sides. 



Tetrathyra. Sternal callosities four — one pair anterior, and 

 one pair lateral. 



Cyclanosteus. 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 mar- 

 ginal bones on the hinder lateral edge. India. 



Emyda. 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. 114, fig. 39 (skull). 



The alveolar surface of the lower jaw flat, as wide in front as be- 

 hind ; 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), Grav, 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 callosi- 

 ties ; 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- 



