226 Trans. Acad. Sci. of St. Louis. 



Cryptodira, and the Chelydoideae, equal to the Pleurodira. 

 Only members of the first group enter our State. 



Superfamily Testudinoideae. 



Neck bending by a sigmoid curve in a vertical plane; cervical verte- 

 brae without or with mere indications of transverse processes; cen- 

 trum of the last cervical articulating with the centrum of the first 

 dorsal. Mandible with articular concavities; outer border of tym- 

 panic cavity deeply notched; pterygoids narrow in the middle, in con- 

 tact on the median line. Pelvis not anchylosed to the carapace and 

 plastron. Digits with not more than three phalanges. Epiplastra in 

 contact with hyoplastra; entoplastron, if present, oval, rhomboidal or 

 T-shaped. A complete series of marginal bones connected with the 

 ribs. 



Family Testudinidae. 



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 estimated as delicacies. (Stejneger.) 



Subfamily Chelydridae. 



Nuchal plate with long costiform processes underlying the marginals. 

 Plastral bones nine. Shell covered with epidermal shields. Caudal 

 vertebrae mostly opisthocoelous. Neck completely retractile within 

 the shell. Temporal region incompletely roofed over. No parieto- 

 squamosal arch. Digits moderately elongate. Phalanges with condyles; 

 claws four or five. 



Genus chelydra. 



No supramarginal shields. Orbit directed outwards and upwards. 

 Tail with large shield inferiorly. 



85. Chelydra serpentina Linnaeus. Common Snapping 

 Turtle. 



Testudo serpentina, Emys serpentina, Chelonura serpentina, Emysaura. 

 serpentina. 



Description. — Head rough, covered with soft skin. Snout short, point- 

 ed. Eyes superior. Interorbital space narrow. A small pointed pro- 



