10 TBIONYCniD^, 



Distribution. Rivers of Asia, Africa, and North America. Of 

 the six known genera, four are represented in the Indian Eegion. 



The Trionychoids are thoroughly aquatic Turtles, living chiefly 

 in rivers ; Pcloclielys even enters the sea. Specimens of Emyda, 

 however, are occasionally found at some distance from water, 

 according to the observations of Kelaart and Blanford. All are 

 carnivorous, and their ferocious habits, together \\ith the extreme 

 rapidity with which they project their necks, render the larger indi- 

 viduals dangerous to men bathing. Of no commercial value. 



Synopsis of Indian Genera. 



A. Plastron without cutaneous valves; hyoplastrou 



distmct from hypoplastron ; no marginal ossi- 

 fications. 

 n. Orbit nearer the temporal than the nasal fossa ; 



bony choanre between the orbits Thionyx, p. 10. 



h. Orbit nearer the nasal than the temporal fossa ; 



bony choanae between the orbits Pelochelys, p. 15. 



c. Orbit nearer the nasal than the temporal fossa ; 



bony choanse behind the orbits Chitba, p. 10. 



B. Plastron with a cutaneous femoral valve, 



under Avhich the hind limb may be con- 

 cealed ; hyoplastron coossified with hypo- 

 plastron ; marginal bones present Emyda, p. 10. 



Genus TRIONYX, 

 Geoffr. Ann. Mus. xiv, 1809, p. 1 (part.). 



Outer extremities of the nuchal plate overlying the second 

 dorsal rib ; neural plates well developed. Limbs completely 

 exposed. Hyoplastron distinct from hypoplastron ; not more 

 than live plastral callosities. Bony choana; between the orbits ; jaws 

 strong; postorbital arch narrower than the diameter of the orbit ; 

 posterior border of pterygoids free, without ascending process. 



Distribution. Africa, Asia, North America. 



15 species are recognized, 7 of which are found in India and 

 its dependencies. The dimensions given are those of specimens in 

 the British Museum : individuals may be found considerably larger, 

 some attaining probably 5 feet in length of carapace. 



Synopsis of Indian Species. 



A. All the costal plates separated on the median 



line by the neural plates; head very large . T. suhplamis, p. 11. 



B. Last pair of costal plates in contact on the 



median line. 

 a. Two neural plates between the first pair 

 of costals; alveolar surface of lower jaw 

 without a strong longitudinal ridge at the 

 .symphysis. 



