TRIONTCniDJE. 241 



Fam. 11. TRIONYCHID^. 



Trionyciclrc, Gra;/, Ann. P/iil. (2) x. li^2o. 



Trionycliidio, JJc/l, Zuul. Joiirn. iii. 1828. 



Steg'iUiopDcle.s, part., Ifdi/frr, Si/tf. A)nph. 1830. 



Trionycid;c, dntij, Si/n. Itcpt. IH.'U. 



PotamitiM, Duiiu'-ril Sf Blhron, Erp. G4n. ii. IS-"!."), 



TrionvcidiC, ^//y///, Cat. Tort. 1844, and Sh. llcpf. i. ISo-j. 



Trioiiyc-Iiiilie, Ai/dssiz, Vunfr. N. II. U. H. i. 1857, 



Triiiiiychida, tStraacli, Clu'lon. Stud. 18G2. 



Chitradas, Trionychidse, Emydinadte, Gray, Suppl. Cat. Sh. Rcpt. i. 



1870. 

 Ti'iouycliid;T3, Cupe, Proc. Amer. Philos. Soc. xx, 1882, p. 143. 



Carapace and plastron -without epidermal shields. Jaws conocaled 

 under tleshylips; snout cudiujj: in a prohoscis. Head and neck 

 coin[)letely retractile. Ear hidden. Oidy the three inner digits 

 clawed. 



llivers of Asia, Africa, and North America. 



Synopsis of tlie Genera. 



I. Plastron without cutaneous valves ; hyoplastron distinct from 

 hypoplastrou ; 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 choanso 

 between the orbits * 1. Trionyx, p. 242. 



Orbit nearer the nasal than the temporal fossa ; bony choana) 

 between the orbits 2. Pelochelys, p. 2G2. 



Orbit much nearer the nasal than the temporal fossa ; bony choanal 

 behind the orbits o. Chitra, p. 2G3. 



II. Plastron with a cutaneous femoral valve, iinder which the 

 hind limb may bo concealed ; hyoplastron coossificd with 

 hypoplastrou ; outer extremities of the nuchal bono under- 

 lying the first costal plate ; jjosterior 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. 2G7. 



Neural plates forming an incomplete, interrupted series ; no marginal 

 bones (J. Cyclanorbis, p. 270. 



* The nasal ducts themselves are, in all Trionychoids, produced posteriorly 

 beyond the level of the orbits. 



