202 



EEPTILIA 



CLASS III 



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

 superfamily recognised by Baur, the Platysternoidea, comprising the family 

 Platysternidae with the solitary genus Flafysternum, Gray. 



Superfamily 4. TESTUDINOIDEA. Baur. 



Skull ivitJiout parieto-squamosal arch, and squamosal separated from postorbito- 

 frontal, with a foramen palatimim. between the palatine and maxilla. Articular 

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

 biconvex. Nuchal without well-developed costiform. processes ; series of inframa,rginals 

 incomplete. 



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



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

 only 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 intergidars wanting. Lateral 

 temporcd arch usually present, quadrate open behind. Digits short and stout, the 

 second and third tvith 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- 



f^tylemys nehrasccnsis, Leidy. 



Fig. 304. 



White River Oligocene ; South Dakota. Plastrou and carapace,- 

 Vs (after Leidy). 



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. 



Emijs, 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. 



