986 The Reptiles of the American Eocene. [December, 



posterior crowns are oval, bean-like bodies, with a median line 

 from which fine incised lines radiate. 



Species with obtusely conic crowns are C. antiqnus Leidy ; C. 

 clavis Cope ; C. clliottii Leidy ; and C. affiuis Marsh. C. subidatus 

 Cope has the crowns acutely conic and curved or straight, while 

 in C acer Cope, they are compressed and have cutting edges. 

 Finally, in C. xipJiodon Marsh, they are much compressed and 

 sharp-edged. 



The Crocoii serratus Cope, of the New Jer- 



sey Eocene, presents the remarkable peculiarity of a finely serrate 

 ridge along the middle line of the front and back of the neural 

 spines of the vertebrae. 



In C. Iietcrodon the osseous scuta of the back are articulated 

 together by suture, as in some of the alligators. 

 Plerodon Meyer. 



This genus only differs from Crocodilus in the presence of two 

 large teeth in each jaw in the position usually occupied by the 

 single so-called canine tooth. It includes the P. rateli, an abun- 

 dant species in the French Miocene. I detected a species in the 

 Wasatch formation of New Mexico, the P. sphcnops Cope. It is 

 about the size of the alligator, and has a narrow muzzle. 



The following list shows the distribution of the Eocene croco- 

 diles now known : 



Puerco epoch. -Three species undetermined. 



Wasatch epoch. Crocodilus wheeleri, C. grvpus, C. heterodon, 

 C. acer. 



Bridger epoch. C. s'ubulatus ; C. sulciferus ; C. xiphodon ; C. 

 polyodon; C.affinis; C. clhotti ; C. clavis. 



Claiborne epoch (marine). C antiquus ; C. fastigiatus ; C. 

 squaukcusis ; C. serratus. 



In general characters, so far as known, there is considerable 

 resemblance between the Eocene and existing species of Croco- 

 dilus. The C. acer, for instance, resembles in the form of its skull 

 the C americanus, of the West Indies and Mexico, but differs in 

 the absence of the strong convexity of the frontal bone, and the 

 more strongly grooved teeth. In general, the recent species have 

 more pronounced cranial ridges than those of the Eocene period. 

 Testudinata. 



The Eocene forms of this order are of unusual interest. I h^ ve 

 seen sixteen species from the Wasatch formation, and thirty-two 



