70 dr. j. e. gray on the trionychidjE. [Jan. 7, 



portional size as regards each other, which may he 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. 



ff 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). 



Hah. Rivers of Western Africa, Niger? (Dr. Baikie). 



Cyclanosteus 



Cyclanosteus, Gray, Suppl. Cat. Sh. Rept. p. 1 1 1, 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., Erpe't. Ge'n. p. 505. 

 Emyda senegalensis, Gray, Cat. Tort. B. M. p. 47; Cat. Sh. 

 Kept. p. 64 ; P. Z. S. 1860, p. 316 (junior). 



