234 Trans. Acad. Sci. of St. Louis. 



Habits. — The habits of the Mud Turtle are strictly 

 aquatic. They prowl about the muddy bottoms of rivers 

 and ponds in search of food. My son caught this turtle 

 in Grinnell's Lake, near Poplar Bluff, Butler Co., April 

 29, June 6, and September 5th. 



Subfamily Emydinae. 



Web-footed turtles having the nuchal plate without costiform lateral 

 processes. 



The terrapins constitute the bulk of the species and genera of turtles, 

 widely distributed in the temperate and tropical countries. They live 

 in streams, lagoons, or on land, and are both vegetable and animal 

 feeders. Some species are highly esteemed as delicacies. (Stejneger.) 



Shell bony, moderately depressed or strongly convex, covered with 

 horny plates, of which there are five dorsals, eight costals, one nuchal, 

 twenty-two marginals, two caudals, twelve sternals, and generally two 

 axillaries, and tv/o inguinals. Head of moderate size, covered with a 

 smooth, soft skin, retractile within the cavity of the shell. Jaws naked. 

 Digits 5-4, generally fully webbed, rarely imperfectly so. 



■ Key to the Geneea in Missouei. 



Plastron and carapace immovably united by a bony symphysis; 

 no hinge across the middle of plastron. 

 Alveolar surface of jaws narrow. 



Alveolar groove well marked, except in front; toes 

 strong, broadly webbed and spreading; hind feet 

 largest; carapace rather flat. Chrysemys. 



Alveolar surface of jaws broad. 



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. 



Alveolar surface of jaws smooth; in front part of 

 upper a deep groove; toes short; head covered 

 with soft skin; upper jaw not notched in front. 



Malaclemys. 



Plastron and carapace united by a cartilaginous lateral suture; 

 plastron hinged across the middle. 



Body short and high; plastron rounded or truncate in 

 front and behind; feet nearly free of webs. 



Terrapene. 



