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 
I llinois. 
Genus Cinosternum, Wagl. 
107. C. pennsylvanicum , Bose. 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 EMYDIDJL 
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 Malaeoclemys. 
b. 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. 
b. 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 
