164 Records of the Indian Museum. [Vor. VII, 
5. Trionyx nigricans, Anderson (pl. v, fig. 5). 
Anderson, Ann. Mag. Nat. Hist., (4), XVI, p. 284 (1875). 
The first pair of costals are separated by two neutal plates. 
The posterior paired bones of the plastron are provided with well- 
developed callosities on which the sculpturing is only a little less 
strong than in T. gangeticus, and in some individuals there is also 
a callosity on the entoplastron. The hyoplastra do not meet in 
the middle line and are strongly divergent posteriorly, although 
they are relatively larger than in 7. phayrei ; their median process 
is single, short, stout and blunt, indistinctly bifid at the tip. The 
epiplastra are narrowerly separated or actually in contact in front 
of the entoplastron. 
The skull is moderately broad, the snout a little longer than 
the diameter of the orbit; the interorbital width is greater than 
that of the nasal fossa and the postorbital arch is about one-third 
as wide as the orbit; the zygomatic arch is horizontal, less 
distinctly curved than in T. phayrei. 
The alveolar surface of the upper jaw bears low median and 
internal longitudinal ridges. ‘The lower jaw has a strong longi- 
tudinal ridge on the symphysis, which is a little longer than the 
orbit ; there is no internal alveolar ridge. 
Anderson describes the external characters as follows :— 
‘“Carapace rather flattened on the back, with the vertebral 
groove ill-defined anteriorly, but well marked posteriorly. Nuchal 
swelling broader than in 7. gangeticus, but not prominent, the 
carapace on either side being flattened. Alae of plastron well 
defined, projecting equally beyond the carapace. Nuchal flap 
narrow, and covered with rather large nodose folds; and the 
hinder portion of the cartilaginous margin of the carapace with 
little nodosities. The rugosities of the osseous carapace coarser 
than in T. gangeticus. 
The under surface of the thighs and tail and of all the soft 
parts, including the head and neck, covered with little papillae. 
No trace of rugosities on the axygos plate of the plastron visible 
through the skin. : 
The tail in the female does not reach to the margin of the 
cartilaginous portion of the carapace. 
Colour of the carapace dark blackish plumbeous, with a tinge 
of olive due to the presence of blackish spots, among which are 
inter-mixed many rusty brown spots, which overlie as it were the 
black spots. The head, neck, and upper surface of the limbs are 
almost black; the upper lip in its two posterior thirds is white; and 
there is a great white blotch over the ear. 
The area between the neck and the four legs is whitish; and 
there are some white spots on the margin of the carapace. The 
head is reticulately spotted; and there is a distinct infraprae- 
orbital band, and a trace of another above the eyes; but the head 
is so black that these markings are difficult to distinguish. The 
under surface of the head and neck is almost black; and the 
