25 



River and Niobrara Tertiaries just mentioned, are frequent in the Bridger 

 beds, and represent several species. 



Remains of lizards also, allied to the modern iguana and monitor, are 

 found as associates of the Bridger fauna. Professor Marsh has likewise 

 reported the discovery of remains of serpents, which he ascribes to several 

 species and genera. 



Multitudes of well-preserved fresh-water fishes are found in the Green 

 River shales. They are chiefly cyprinodonts and herrings, and, for the most 

 part, have been described by Professor Cope. 



Black, shining, enameled scales, teeth, and vertebras of ganoid fishes are 

 frequent among the fossils of the Bridger beds. 



The Tertiary strata of Green River and its tributaries, including the 

 latter, as indicated by the character of the vertebrate fossils, are much older 

 than the tertiaries of the Mauvaises Terres of White River, Dakota, and of 

 the Niobrara River, Nebraska. They overlie the cretaceous rocks, with which 

 they are unconformable, and they are probably contemporaneous with the 

 Eocene formations of Europe. 



Attention was first directed to the Green River Tertiary formation, 

 which has proved to be so rich in the remains of vertebrates, by the late Dr. 

 John E. Evans, as early as 1856. From Green River he obtained a speci- 

 men of shale, with a well-preserved fish, represented in Fig. 1, Plate XVII, 

 of the present work, and briefly described by the writer, under the name of 

 Clupea humilis, in the proceedings of the Academy of Natural Sciences of 

 Philadelphia, for October, 1856. 



In 1868 Dr. J. Van A. Carter, of Fort Bridger, in correspondence with 

 the author, informed him of the frequent occurrence of the remains of turtles 

 and other animals in the buttcs of the neighboring country. The same year 

 Professor Hayden, during his geological explorations, obtained remains of a 

 Trionyx from Church Buttcs. Colonel John H. Knight, United States Army, 

 also procured a vertebra of an extinct crocodile from the same formation of 

 Bitter Creek. These remains, together with those of a small insectivorous 

 animal, discovered by Dr. Carter on the Twin Butte, near Fort Bridger, were 

 described by the writer in the Proceedings of the Academy for April, 1869. 

 The little insectivore was named Omomys Carieri in honor of its discoverer, 

 and is also described in " The Extinct Mammalian Fauna of Dakota and 

 Nebraska." The specimen upon which it was characterized is represented in 

 4 G 



