CEOCODILIA. 151 



Measurements. 



If. 



Length of an anterior marginal scute 045 



Width of an anterior marginal scute 039 



Thickness of bone at anterior marginal scute 023 



Length of a free marginal bone 050 



Width of a free marginal bone 057 



Length of first marginal of bridge 060 



Thickness at simple end 023 



From the bad lands of Ham's Fork, AVyoraing. 



CKOOODILIA. 



The fauna of the Eocene periods of the United States inckided a num- 

 ber of species of Crocodilia, some of which were represented by great 

 numbers of individuals. They were equally numerous in the Wasatch and 

 Bridger epochs, but none have been found in the Green River fomiation 

 proper. They are moderately abundant in the Wind River beds, and a 

 species is known from the Manti beds of Utah. None are known from 

 the Miocene formations west of the Rocky Mountains, and but one species 

 from that formation to the east of them ; but they are not rare in the marine 

 Miocene of the Atlantic coast. All the species belong to two genera, Diplocy- 

 nodus Pomel, and Crocodilus Linn. One species of the former is found in 

 the Wasatch beds, with three or four species of Crocodilus. In the Bridger 

 beds I know of six species of the latter genus. 



CROCODILUS Linn. 



The Eocene species of true crocodiles differ much in size and characters, 

 ranging from the C heterodon, which is not larger than an Iguana, to the 

 C. clavis, which rivals the existing species of the East Indies. 



The species are divided into two sections, which are distinguished by 

 the form of the frontal bone. In the one it is thin, and has low lateral olfac- 

 tory crests. Such species are as yet only known from the Wasatch forma- 

 tion. They are the G. grypm Cope and C. wheeleri Cope. Thq. species of the 

 second section have massive frontal bones with strong lateral olfactoiy 

 crests. The C. chamensis and C. heterodon of the Wasatch belong here ; 

 also the C. eUiottii of the Bridger and the C. clavis of the Washakie forma- 

 tion. The frontal bones of C. subulatus and C. polyodon of the Bridger are 



