342 Records of the Indian Museum. [VoL oes 
The skull (pl. x xxiii, figs. 1, 1a) resembles that of T. gangeti- 
cus in general appearance, but is considerably smaller and nar- 
rower. ‘The interorbital space is slightly concave and consider- 
ably narrower than either the nasal cavity or the orbit; the post- 
orbital arch is rather more than half as broad as the orbit and the 
post-orbital foramen remarkably small. The snout is longer than 
the orbit and distinctly declivous; it is more pointed than in 
T. gangeticus, but less so than in 7. hurum and T. leithii. The 
symphysis of the lower jaw is long, equalling the orbit in length; 
the jaw itself is bluntly pointed; there are no ridges either longi- 
tudinal or transverse in this region; the two rami are more con- 
vergent than in 7. gangeticus. 
i) 
I 
Fic. 1.—Head of Trionyx sulcifrons (from life), 3 nat. size. 
,  2.—Head of Trionyx gangeticus mahanaddicus (from type specimen), 
1 14 
} nat. size. 
The branchial skeleton resembles that of T. gangeticus,’ but 
the greater cornua are more slender and the ceratobranchials 
stouter and shorter; the hypobranchials are distinct and show 
traces of segmentation into 2 or 3 pieces; this is, however, less 
marked than in T. gangeticus. 
The margin of the bony carapace is concave in front and 
almost straight behind ; the sculpturing of the posterior region is 
coarser than that of the anterior and near the posterior border 
there are small scattered bony tubercles. There are two or three 
neural plates between the first pair of costals. The plastron 
closely resembles that of T. gangeticus, but the hypoplastra and 
hyoplastra of the two sides apparently remain widely separated 
in the adult and all the bones are smaller. 
1 Annandale, Rec. /nd. Mus. VU, p. 159, fig. 1 (1912). 
