12 TBIONYCHID.i;. 



narrow, forming a keel on its outer surface ; mandibular symphysis 

 shorter than the diameter of the orbit, without median ridge. 

 Brown above, yellowish beneath and on the sides of the neck ; 

 head and neck with yellowish dots ; some young with an oblique 

 dark streak behind each eye. 



Length of dorsal disk 10 inches. 



Hal. Mergui, Malay Peninsula, Sumatra, Borneo, Java. 



5. Trionyx gangeticus. 



Trionyx gangeticus, Cuvier, Oss. Foss. \, pt. 2, pp. 186, 222, pi. xi, 



tigs. 5-8 ; Souleng. Cat. CM. Sfc. p. 248. 

 Trionyx javanicus (non Geoffr.}, Gray, III. Ind. Zool. ii, pi. Ixv ; 



Giinth. Kept. .#. /. p. 48. 



Aspilus gataghol, Gray, A. M. N. H. (4) x, 1872, p. 339. 

 Trionyx gangeticus, part., Theob. Cat. p. 28. 



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

 throughout on the median line ; two neurals between the first 

 pair of costals ; plates coarsely pitted and vermiculate. Epiplastra 

 narrowly separated from each other in front of the entoplastron, 

 which forms an obtuse or a right angle ; plastral callosities very 

 large, hyo-hypoplastral, xiphiplastral, and, in old specimens, ento- 

 plastral. Dorsal skin of young with longitudinal ridges of small 

 tubercles. Head moderate ; snout (on the skull) about as long as 

 the diameter of the orbit ; interorbital region, in the adult, con- 

 siderably narrower than the nasal fossa ; postorbital arch one third 

 to one half the greatest diameter of the orbit ; mandible with the 

 inner edge strongly raised, forming a sharp ridge, which sends off 

 a short perpendicular process at the symphysis ; the diameter of 

 the mandible at the symphysis does not exceed the diameter of the 

 orbit. Olive above ; back of young vermiculated with fine black 

 lines, but without ocelli ; head with a black longitudinal streak 

 from between the eyes to the nape, intersected by two or three 

 A-shaped black streaks ; lower parts yellowish. 



Length of dorsal disk 2 feet. 



Hab. Gangetic river-system ; Indus ? 



6. Trionyx leithii. 



Trionyx leithii, Gi-ay, A. M. N. H. (4) x, 1872, p. 334; Bouleng. 



Cat. Chel. 8fc. p. 249. 

 ? Trionyx gangeticus, Murray, Zool. Sind, p. 342. 



Intermediate between T. gang elicits and T.lmrum. Agrees with 

 the former in the width of the interorbital space, the comparatively 

 short mandibular symphysis, and the markings of the head ; with 

 the latter in the longer and more pointed snout, the absence of a 

 strong ridge on the inner alveolar surface of the mandible, and in 

 the presence, in the young, of four or more dorsal ocelli, which are, 

 however, smaller than in T. hurum. 



Hab. Kistna Eiver, Deccan, and Nelambar Eiver, Malabar. 



This will probably prove to be a Peninsular form, ranging from 

 the Indus to Madras and Malabar. 



