1873.] DR. J. E. GRAY ON THE TRIONYCHIDjE. 65 



sities, like the Trionyx, very unlike the narrow transverse callous band 

 on the edges of the central suture in Aspilus. The hinder sternal 

 bones are smooth. 



The skull is exceedingly like that of Trionyx ; but the front of the 

 upper jaw is broader and rounded in front. The distance between the 

 orbit and large quadrangular transverse nose-hole is not half the length 

 of the diameter of the large orbit. The alveolar surface of the upper 

 jaw is moderate, rather narrow in front, and gradually rather broader 

 at the hinder part. The longitudinal depression in front of the 

 inner nostrils is moderately deep, rounded in front, and rather 

 broader behind. 



1. Rafetus euphraticus. (Fig. 12, p. 66.) 



Testudo rafeht, Oliv. Voy. Pers. ii. p. 453, t. 41 (copied, Shaw's 

 Miscell. t. 2. p. 907). 



Testudo euphraticus, Daud. Rept. ii. p. 305 (from Olivier). 



Trionyx euphraticus, Geoff. Ann. Mus. iv. p. 17 (from Olivier). 



Gymnopus euphraticus, Dum. et Bibr. Erp. Gen. ii. p. 498. 



Tyrse rafeht, Gray, Cat. Tort. Brit. Mus. p. 49. 



Trionyx rafeht, Gray, Cat. Sh. Rept. Brit. Mus. p. 85, t. 30. 



Rafetus euphraticus, Gray, P. Z. S. 1864, p. 81, 1869, p. 213; 

 Suppl. Cat. Sh. Rept. p. 104. 



Hab. Euphrates (Chesney and Loftus); Tigris (Olivier). 



C. Dorsal disk truncated in front, with the odd bone separate from 

 it, and with a rounded central callosity in the adult ; lateral 

 bones of the sternum expanded, with a narroio linear callosity 

 on each side of the central suture ; posterior pair of bones 

 slender, not dilated, without callosities. 



The dorsal disk is truncated or concave on the front edge ; the 

 front edge of the first vertebral bone is generally rounded and pro- 

 minent in front towards the rounded callosity in the middle ot 

 the separate front odd bone. 



Aspilus. 



Aspilus, Gray, P. Z. S. 1864, p. 84, f. 4-6 ; Suppl. Cat. Sh. Rept. 

 p. 102, f. 33 (skull). 



Skull tapering in front ; the short space between the square nose- 

 hole and the orbits less than half the diameter of the latter, 

 which are large and rather close ; palate broad, rather deep, of the 

 same width the whole length ; alveolar process broad behind, 

 gradually narrower in front. Lower jaw with a concave alveolar 

 surface, rather broad in front, with a central longitudinal ridge, more 

 prominent in the centre of its length, and with a somewhat deeper 

 concavity on each side of the ridge. 



The young specimens have the odd bone in front of the dorsal 

 disk separate, smooth, and covered with the skin. In the older spe- 

 cimens it becomes nearer to lie front edge of the dorsal disk, and has 

 a small circular central callosity. 



Proc. Zool. Soc— 1873, No. V. 5 



