249 TRIONYCHID 2, 
1. TRIONYX. 
Emys, part., Dumér. Zool. Anal. p. 76 (1806). 
Trionyx, part., Geoffr. Ann. Mus. xiv. p. 1 (1809) ; Fitzing. N. Class. 
Rept. p. 7 (1826) ; Gray, Syn. Rept. p. 45 (1881); Strauch, Chelon. 
Stud. p. 50 (1862). 
Aspidonectes, Wagler, Syst. Amph. p. 184 (1830) ; Agassiz, Contr. 
N. H. U.S. i. p. 403 (1857). 
Gymnopus, part., Dum. § Bibr. ii. p. 472 (1835). 
Platypeltis, Hitzing. Ann. Wien. Mus. i. p. 127 (1885) ; Agassiz, l. c. 
p. 400; Gray, Suppl. Cat. Sh. Rept. 1. p. 107 (1870), and Proc. 
Zool. Soe, 1878, p. 58. 
Pelodiscus, F%tzing. 0. e. 
Amyda, Fitzing. l. c.; Agassiz, 1. c. p. 898 ; Gray, Ul. cc. pp. 95, 62. 
Tyrse, Gray, Cat. Tort. p. 47 (1844), and ll. ec. pp. 107, 62. 
Trionyx, Gray, Cat. Tort. p. 49, and Sh. Rept. i. p. 64 (1855) ; 
Giinth. Rept. Brit. Ind. p. 46 (1864) ; Gray, Suppl. Cat. Sh. Rept. 
i. p. 97, and Proc. Zool. Soc. 1873, p. 47. 
Dogania, Gray, Ul. cc. pp. 49, 69, 105, 56. 
Rafetus, Gray, Proc. Zool. Soc. 1864, p. 81, and Suppl. Cat. Sh. 
Rept. i. p. 103, and Proce. Zool, Soc. 1873, p. 64. 
Aspilus, Gray, ll. cc. pp. 83, 101, 65. 
Potamochelys, part., Gray, Proc. Zool. Soc. 1864, p. 85, and Suppl. 
Cat. Sh. Rept. i. p. 104. 
Landemania, Gray, Proc. Zool. Soe. 1869, p. 215, and Suppl. Cat. 
Sh. Rept. i. p. 96, and Proc. Zool. Soc, 1878, p. 53. 
Fordia, Gray, ll. ce. pp. 219, 96, 43. 
Callinia, Gray, Ul. cc. pp. 221, 108, 60. 
Sarbieria, Gray, Proc. Zool. Soc. 1869, p. 220, and Suppl. p. 100. 
Nilssonia, Gray, Ann. §& Mag. N. H. (4) x. p. 3382 (1872), and Proc. 
Zool. Soe. 1873, p. 45. 
Isola, Gray, Proc. Zool. Soc. 18738, p. 51. 
Ida, Gray, 1. c. p. 55. 
Oscaria, Gray, Ann. § Mag. N. H. (4) xii. p. 157 (1878). 
Yuen, Heude, Mém. Hist. Nat. Emp. Chin. 1. p. 18 (1880). 
Psilognathus, Heude, l. c. p. 24. 
Temnognathus, Heude, 1. c. p. 25. 
Gomphopelta, Heude, 1. c. p. 27. 
Ceelognathus, Heude, l. ec. p. 29. 
Tortisternum, Heude, 1. ¢. p. 31. 
Ceramopelta, Heude, . ¢. p. 33. 
Coptopelta, Heude, 1. ¢. p. 34. 
Cinctisternum, Hevde, 1. c. p. 36. 
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 five plastral 
callosities. Bony choanz between the orbits; jaws strong; post- 
orbital arch narrower than the diameter of the orbit; pterygoids, 
posterior border free, without ascending process. 
Africa, Asia, North America. 
The fact that the width and shape of the alveolar surfaces of 
the jaws may vary considerably in Turtles of this genus which, in 
all other respects, must be regarded as closely related or even 
identical, was first pointed out by Agassiz, who seized upon the 
