2(10 TRIONYCHIDiE. 



Gymnopus spiniferus, part., Dum. ^- Bibr. ii. p. 477, pi. xxii. fig. 1 



(1835). 

 Trionyx ferox, Dehmj, N. Y. Faun. iii. p. 6, pi. \\. fig. 11 (1842). 

 Tyrso argus, Gray, Cat. Tort. p. 48 (1844), and Knowsleij Menay. 



pi. — (1846). 

 Trionyx argus, Gray, Cat. Sh. Rept. i. p. G8 (1855). 

 Aspidonectes spiiiifcr, Ayassiz, Contr. N. H. U. S. i. p. 403, pi. vi. 



figs. 1 & 2 (1857). 

 Gymnopus olivaceus, Wiecl, N. Act. Ac. Leop.- Carol, xxxii. i. p. 55, 



pi. V. (1865). 

 Calliuia spinifera, Gray, Proc. Zool. Soe. 1869, p. 222, and Snppl. Cat. 



Sh. Rept. i. p. 109 (1870), and Proc. Zool. Soe. 1873, p. 60, figs. 



Very closely allied to the preceding, but carapace flatter *, snout 

 and interorbital region narrower, and markings different. Dorsal 

 disk with small black spots and ring-like markings, which may 

 become indistinct with age ; young with a pale, black-edged border 

 to the dorsal disk ; a light, black-edged streak on each side of the 

 head, passing through the eye, uniting with its fellow at the base 

 of the proboscis ; limbs spotted and marbled with black. 



Length of dorsal disk 30 centim. 



Middle and Northern tributaries of the Mississippi ; Ohio ; Saint 

 Lawrence River. 



a. Hgr., spir. Foxbmy, Pensylvania. Smithsonian Institution. 



b. Ilgr., spir., skull Wabash River, 

 separate. 



c. d, e. Hgr. & yg., N. America, 

 spir. 



/. Hgr., stfid. ? Lord Derby [P.]. (Type 



of 7'. aryus.) 



15. Trionyx mtiticus t- 



Trionvx muticus, Lesueur, Mem. Mus. xv. p. 263, pi. vii. (1827) ; 



Leconte, Ann. Lye. N. Y. iii. p. 95 (1830) ; Holbr. N. Am. Herp. 



ii. p. 19, pi. ii. (1842) ; Gray, Cat. Tort. p. 50 (1844), and Sh. 



Rept. i. p. 69 (1855) ; Strauch, Chelon, Stud, p. 174 (1862), and 



Verth. Schildkr. p. 125 (1865). 

 Gymnopus muticus, Dum, Sf Bibr. ii. p. 482 (1835). 

 Amyda mutica, Ayassiz, Contr. N. H. U. S. i. p. 399, pi. vi. figs. 6 & 



7 (1857) ; Gray, Suppl. Cat. Sh. Rept. i. p. 95 (1870) ; Baur, 



Zool. Anz. 1887, p. 99. 

 Potamochelys ? microcephala. Gray, Proc. Zool. Soe. 1864, p. 87. 

 Callinia microcephala. Gray, Proc. Zool. Soe. 1869, p. 222, and Suppl. 



Cat. Sh. Rept. i. p. 108, and Proc. Zool. Soe. 1873, p. 62, figs. 



Differs from the preceding in the much narrower, sharply pointed 

 snout, the absence of conical tubercles on the anterior border of the 

 dorsal disk and on the posterior cartilaginous margin, and in the 

 absence of a papilla on each side of the nasal septum, which is 

 considerably wider than in other Trionychoids. Entoplastron, in the 



* A small eighth pair of costal plates is present in one of our specimens. 

 t In addition to the single specimen in the Museum, I have recently examined 

 a fully adult living specimen, from which the following notes are taken. 



