14 THIONYCHIDjE. 



border of shell light-dotted ; head with large yellow spots, viz. 

 across the snout, behind the orbit, at the angle of the mouth, 

 on the tympanic region, and on the chin ; these spots become 

 indistinct in the adult, the head of which is more or less closely 

 spotted or vermiculated with black ; dorsal disk in the young with 

 dark marblings and four or six very large ocelli. 



Length of dorsal disk 16 inches. 



Hob. Granges and its tributaries. 



8. Trionyx formosus. 



Trionyx formosus, Gray, P. Z. S. 1869, p. 217, pi. xv, fig. 1 ; Theob. 



Cat. p. 31 ; Bouleng. Cat. Chel. $c. p. 250. 



Trionyx peguensis, Gray, Supjjl. Cat. Sh.Rept. i, p. 99 ; Theob. Cat. p. 31 . 

 Trionyx grayii, Theob. P. A. S. B. 1875, p. 176, pi. iii ; id. Cat. p. 31. 



Costal plates eight pairs, the last well developed and in contact 

 throughout on the median line ; a single neural between the first 

 pair of costals ; plates coarsely pitted and verrniculate. Dorsal 

 skin of young with longitudinal ridges of small tubercles. Epi- 

 plastra separated from each other ; entoplastron forming an obtuse 

 or right angle ; plastral callosities well developed, hyo-hypoplastral 

 and xiphiplastral, and coarsely sculptured like the carapace. Head 

 moderate : snout (on the skull) about as long as the diameter of 

 the orbit ; interorbital region, in the adult, as broad as the nasal 

 fossa ; postorbital arch, in the adult, a little less than half the 

 diameter of the orbit ; mandible with a strong ridge along the 

 symphysis, the diameter of which equals or a little exceeds that 

 of the orbit. Olive-brown above, white below; head of young 

 ornamented with yellow black-edged markings, the largest being 

 a cross-band on each side of the back of the head ; these markings 

 disappear in the adult, the head of which is closely spotted with 

 black above and uniform white inferiorly ; young with four large 

 dorsal ocelli, as in T. hurum. 



Size of T. hurum. 



Hah. Irrawaddy, Sittoung, and Salween rivers, Burma. 



9. Trionyx phayrii. 



Trionyx phayrei, Theob. Journ. Linn. Soc. x, 1868, p. 18 ; id. Cat. 



p. 30; Bouleng. Cat. Chel. #c. p. 251. 

 Trionyx jeudi. Gray, P. Z. S. 18H9, p. 217, figs. 

 Trionyx cariniferus (non Gray), Theob. P. A. S. B. 1874, p. 80, pi. iv. 



Costal plates eight pairs, the last well developed, with slightly 

 concave posterior border, and in contact on the median line ; a 

 single neural between the first pair of costals ; plates rather 

 coarsely pitted and vermiculate. Epiplastra in contact in front of 

 the entoplastron, which forms an obtuse or right angle ; plastral 

 callosities hardly developed, the hyoplastra bearing a mere trace of 

 sculpture. Head moderate ; skull as in T. formosus, but snout a 

 little longer in the adult. Head of adult spotted or vermiculated 

 with black above and uniform whitish inferiorly, as in T. formosus. 



Length of dorsal disk 20 inches. 



Hob. Pegu, Arrakan range, Tenasserim and Sumatra. 



