TRIONYCHID. O41 
Fam. 11. TRIONYCHIDA. 
Trionycide, Gray, Ann. Phil. (2) x. 1825. 
Trionychide, Bell, Zool. Journ, iii. 1828. 
Steganopodes, part,, Wagler, Syst. Amph. 1830. 
Trionycidee, Gray, ‘Syn. Rept. 1831. 
Potamites, Duméril § Bibron, Erp. Gén. ii. 1855. 
Trionycidee, Gray, Cat. Tort. 1844, and Sh. Rept. i. 1855. 
Trionychidee, Agassiz, Contr. N. H. U. 8. i. 1857. 
Trionychida, Strauch, Chelon. Stud. 1862. 
Chitrade, Trionychidee, Emydinade, Gray, Suppl. Cat. Sh. Rept. i. 
1870. 
Trionychid, Cope, Proc. Amer. Philos, Soc. xx. 1882, p. 145. 
Carapace and plastron without epidermal shields. Jaws concealed 
under fleshy lips; snout ending in a proboscis. Head and neck 
completely retractile. Kar hidden. Only the three inner digits 
clawed. 
Rivers of Asia, Africa, and North America. 
Synopsis of the Genera. 
I. Plastron without cutaneous valves ; hyoplastron distinct from 
hypoplastron ; outer extremities of the nuchal bone overlying 
the second dorsal rib; posterior border of the pterygoids 
free, without median process ; walls of the labyrinth com- 
pletely exposed behind. 
Orbit nearer the temporal than the nasal fossa; bony choanw 
between the orbits * 
ee on 1. Trionyx, p. 242. 
Orbit nearer the nasal than the temporal fossa; bony choanse 
between the orbits. 2.3 6¢..9..6 se ae 2. Pelochelys, p. 262. 
Orbit much nearer the nasal than the temporal fossa; bony choane 
DeMIMds CHS: OLDIES esr crass theests suas oe 3. Chitra, p. 263. 
II. Plastron with a cutaneous femoral valve, under which the 
hind hmb may be concealed; hyoplastron coossified with 
hypoplastron ; outer extremities of the nuchal bone under- 
lying the first costal plate; posterior border of pterygoids 
with a median ascending process forming a suture with the 
opisthotic, behind the labyrinth. 
Neural plates forming a complete series; no marginal bones. 
4. Cycloderma, p. 265. 
Neural plates forming a complete series ; marginal bones present. 
5. Emyda, p. 267. 
Neural plates forming an incomplete, interrupted series ; no marginal 
DOTS iret 1, care a yuma ac eek dare Nea ners 6. Cyclanorbis, p. 270. 
* The nasal ducts themselves are, in all Trionychoids, produced posteriorly 
beyond the level of the orbits, 
