54 NORTH AMERICAN BATRACHIA AND REPTILIA, 



imbricated; edged with black, and with black lines or dots radi- 

 ating from their posterior portion to their front and lower mar- 

 gins; no stripes along neck. Louisianian district; Northern 

 Illinois. 



Genus Cinosternum, Wagl. 



107. C. pennsylvanicum., Bosc. Mud Turtle. Jaws strong, 

 and hooked in front; scales smooth; color above dusky-brown; 

 below variable, yellowish to chestnut; head dark, with light 

 dots; throat yellowish. -Austroriparian and. Eastern sub-regions. 



Family EMYDID^. 



A. Plastron and carapace immovably united by a bony sym- 

 physis; no hinge across middle of plastron. 



a. Alveolar surface of jaws broad. 



1. Alveolar surface of upper jaw with a submedian 



ridge, parallel to margin; toes short and 

 strongly webbed; head with thin, hard skin; 

 upper jaw notched in front Pseudemys. 



2. Alveolar surface of jaws smooth; in front part 



of upper a deep groove; toes short; head cov- 

 ered with soft skin; upper jaw not notched in 



front Malaooclernys. 



h. Alveolar surface narrow. 



1. Alveolar groove well marked, except in front; 



toes strong, broadly webbed and spreading; 

 hind feet largest; carapace rather flat. 



Chrysemys. 



2. Carapace considerably arched; toes with a small 



web; feet nearly equal in size; species small. 



Chelopus. 



B. Plastron and carapace united by a cartilaginous lateral 

 suture; plastron hinged across the middle. 



a. Carapace somewhat depressed; plastron more or less 

 emarginate behind; feet strongly webbed. . .Emys. 



h. Body short and high; plastron rounded or truncate 

 in front and behind; feet nearly free of webs. 



Cistudo. 



Genus Pseudemys, Gray. 



A. No scales upon loose skin between legs; ridge on alve- 

 olar surface of upper jaw tuberculate; shield in young covered 



