206 EEPTILIA : TESTUDINATA. — XXX. 



aa. Nostrils terminal, crescent-shaped ; a prominent longitudinal ridge project- 

 ing from each side of septum ; head broad ; edge of upper jaw entire. 



ASPIDONECTES, 306. 



305. AMYDA Agassiz. (Lat., turtle.) 

 509. A. mutica (Le Sueur). Leather-Turtle. A depres- 

 sion along median line of carapace ; no spines nor tubercles along 

 anterior margin nor on back. Olive, young spotted ; feet not mot- 

 tled below. L. 12. Canada to Ohio R., and N. W. (Lat., un- 

 armed.) 



306. ASPIDONBCTES Wagler. (dtrrTis, shield ; i/ij/cn^s, 

 swimmer.) 

 a. Lower parts of body and feet spotted with dark. 



600. A. spinifer (Le Sueur). Common Soft-shelled Tur- 

 tle. Carapace olive brown with dark spots ; head and neck olive 

 green with light and dark stripes ; legs and feet mottled every- 

 where with dark ; ^ with the tubercles on the front of the carapace 

 smaller than in the 9 , the body also longer and the tail extending 

 considerably beyond the margin of the carapace. Canada to Ky. 

 and Minn., abundant. (Lat., spine-bearing.) 



601. A. nuchalis Agassiz. A marked depression on either side 

 of the blunt median keel, which is dilated and triangular anteriorly ; 

 spines and tubercles prominent in ^. Cumberland and LTpper 

 Tenn. Rivers. 



aa. Lower parts of body and feet white. 



602. A. agassizi Baur. Tubercles on shell largest in ^; back 

 blotched in adult ; young with black spots and ocelli and with 2 or 

 3 concentric black marginal lines. S. Ind. to Ga. and La. 



Family CXX. CHBLYDRID.^. (The S-Xapping 



TUKTLES.) 



Shell high in front, low behind ; body heaviest forward ; head and 

 neck very large, the snout narrowed forward; jaws strongly hooked, 

 and very powerful ; tail long, strong, with a crest of horny, com- 

 pressed tubercles ; plastron small, cross-shaped, with 9 plates be- 

 sides the very narrow bridge. Claws 5-4, strong, the web small. 



Large turtles of great strength and voracity, chiefl\- aquatic ; 2 

 of the 3 species are American, the third (Plalysternnm) is from 

 China. 



a. Eyes close together, partly superior; head covered with soft skin ; tail mtli 

 two rows of moderate scales beneath ; ridges of carapace becominn- obsolete 



with age; jaws moderately hooked Cheia'dra 307. 



aa. Eyes distant, lateral; head very large, covered with smooth, symmetrical 

 plates ; tail with many small imbricate scales beneath ; carapace with 3 

 large persistent keels; jaws very strongly hooked. 



ALVCROCHELYS, 308. 



