156 



Key to the Gene k a of Testudinidce. 



A. Parts of tlie plastron immovably sutured to one another and to 

 tlie carapace, 

 a. Alveolar surface of the upper jaw Avith a median ridge par- 

 allel with the cutting edge of the jaw. 



Chrysemys, p. 156. 

 aa. Alveolar surface without a ridge. 



b. Alveolar surface broad. Choanse even with posterior 



borders of the orbits. Malademys, p. 164. 



bb. Alveolar surfaces narrow. Choanse between the eyes. 



Clemmys, p. 168. 

 AA. Plastron with at least its anterior lobe movable on a transverse 

 ligamentous hinge. 



c. Upper jaw not hooked. Shell two-thirds as wide as 



long. Emydoidea, p. 170. 



cc. Upper jaw hooked. Shell three-fourths as wide as 



long. Cistuda, p. 171. 



Genus CHRYSEMYS, Gray. 



Chrysemys, Gray, 1844, 91, 27 ; Boulenger, 1889, 84-, 69 ; Pseudemys, 

 Gray, 1855, 25, 33; Ptychemys, Trachemys, and Chrysemys, Agassiz, 1857, 

 4, i, 431, 434 and 438. 



Shell moderately depressed. Bridge wide ; the axillary and inguinal 

 processes of the carapace (seen in the skeleton) well developed, the latter 

 united to the 5th costal plate. Entoplastron lying wholly in front of the 

 suture between the humerals and the pectoral scutes. Alveolar surfaces 

 of the jaws broad, that of the upper with a median ridge parallel with 

 the cutting edge of the jaw. Choanse well toward the antei'ior border of 

 the eyes. Hind legs stout, all the digits webbed beyond the bases of 

 the claws. Skull with a bony arch bounding the eyes behind (temporal 

 arch). 



Key to the Indiana Species of Chrysemys. 



A. Alveolar surface of the upper jaw broad, with the median ridge 

 tuberculated. Upper jaw slightly or not at all notched in 

 front. (Ptychemys, Ag.) 

 a. Cutting edges of both jaws smooth or nearly so ; tubercles 

 of alveolar surface not prominent. Shell quite flat, 

 deeply serrated behind. Plastron with its hinder bor- 

 der distinctly notched. Head small. 



hieroglyphica, p. 157. 



