1873.] dr. j. e. gray on the trionychidji. 4? 



3. Trionyx. 



Trionyx, Gray, P. Z. S. 1864 j Suppl. Cat. Sh. Rept. p. 88, fig. 32. 



Palate of the skull with a broad shallow concavity to the internal 

 nostrils, of the same width before and benind. 



The alveolar surface of the lower jaw is usually more or less con- 

 cave, and often marked with a central longitudinal ridge over the 

 suture of the jaw. 



The form of the alveolar surface, and the comparative width of 

 various parts of it, and the various concavities and ridges on the dif- 

 ferent parts of its surface afford excellent characters for the species. 



The dorsal disk in the young animals is generally marked with 

 three pairs of black spots, which have concentric pale rings within. 

 These spots often last, in a more or less perfect degree, through the 

 life of the animal. Sometimes the anterior, and sometimes the 

 posterior pair, and rarely a spot on one side of these pairs, are de- 

 ficient. The crown of the head of the young specimens is generally 

 marked with spots of various colours, which become more and more 

 indistinct as the animal grows. I believe that these spots are cha- 

 racteristic of the species ; and sometimes whole series of species 

 have characteristic spots — that is to say, on the side of the crown 

 and face. 



The skulls of the species of this genus which we have in the 

 British Museum may be divided into two sections : — 



1. Nose of skull broad, rounded in front. Trionyx gangeticus. 



2. Nose of skull tapering, converging in front. T. sewaare, T. 

 jeudii, T. leithii. 



* Crown of head olive, with radiating black lines behind. 

 I. Trionyx gangeticus. The " Dekoolee." (Plate VIII.) 



Skull short, broad ; nose suddenly bent down, with a rounded out- 

 line. Eyes within a very short distance of the cavity of the nostrils, 

 which is not as long as the diameter of the orbit ; alveolar surface of 

 the lower jaw deeply concave, with a very slight indistinct central 

 longitudinal ridge. 



The Dekoolee, Hardwicke, icon. ined. 



Trionyx du Ganges, Cuvier, Oss. Foss. v. pt. 2. p. 187, tab. ii. 

 figs. 5-8 (skull). 



Trionyx gangeticus, " Duvaucel," Cuvier, Regne Animal, vol. ii. 

 p. 16 ; Gray, Cat. Sh. Rept. B. M. p. 66, tab. 42. fig. 1 ; Suppl. p. 97, 

 fig. (skull only). 



Gymnopus duvaucelii, Dumeril and Bibr. Erpet. Generale, vol. ii. 

 p. 47. 



Aspidonectes gangeticus, Wagler, Amphib. Taf. ii. figs. 13-22; 

 copied from Cuvier. 



Trionyx javanicus, Gray, Cat. Sh. Rept. p. 67 (not synonyma). 



Potamochelys stellata, Gray, Suppl. Cat. Sh. Rept. B. M. p. 104 

 (animal only, not skull). 



Variety 1 The black lines irregular. 



