202 



REPTILIA 



CLASS III 



without representatives in the fossil state. The same is true of the third 

 superfamily r.ecognised by Baur, the Platysternoidea, comprising the family 

 Platysternidae with the solitary genus Flatysternum, Gray. 



Superfamily 4. TESTUDINOIDEA. Baur. 



Skull without parieto-squamosal arch, and squamosal separaied from iiostorhito- 

 frontal, with a foramen palatinum hetween the palatine and maxilla. Articulm 

 faces hetween the sixth and seventh cervical vertebrae not plane, and two of the cervicals 

 biconvex. Nuchal without well-developed costiform processes ; series of inframo/rginals 

 incom 



Family 1. Emydidae. Gray. (Marsh Turtles.) 



Shell completely ossified in the adult, covered with epidermal shields. Carapace 

 onhj moderately convex. Plastron sometimes hinged, with long sternal bridge and 

 large sternal Chambers, the marginals of bridge without median processes interlocking 

 with the rib-ends. Plastral bones nine, mesoplastron and intergulars wanting. Lateral 

 temporal arch usually present, quadrate open behind. Digits short and st out, the 

 second and third ivith more than two phalanges ; claws four or five. Tertiary and 

 Recent. 



The Emyds or Marsh Turtles are very closely related to the Land Tortoises, 

 and are sometimes included with them in the same family. The shell, how- 



Stylemys nebrascensis, Jjeidy. 



Fig. 304. 



White River Oligocene ; South Dakota. 

 1/3 (after Leidy). 



riastrou and carapace, 



ever, in the Emyds is less convex, the sternal Chambers are larger, and their 

 limbs are without dermal ossifications. Their distribution at the present day 

 is World -wide with the exception of the Australian region. Fossil marsh 

 turtles make their first appearance in the Eocene, and belong for the most 

 part to existing genera. 



Emys, Dumeril (Lutremys, Gray). Neural bones short, hexagonal ; nuchal 

 not distinctly emarginate. Plastron united to the carapace by ligament, and 

 more or less hinged in the adult. Eocene to Recent. 



