25 



River iind Niobrara Tertiaries just mentioned, are frequeiil in the Ijiidger 

 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 cypi'inodonts and herrings, and, for the most 

 part, have been described by Professor Cope. 



Black, shining, enameled scales, teeth, and vertebrae of ganoid fislies are 

 frequent among the fossils of the Bridger beds. 



The Tertiary strata of Green River and its tributai'ies, including the 

 latter, as indicated l)y the character of the vertebrate fossils, are much older 

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

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

 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 tlie remains of vertebrates, by the late Dr. 

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

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

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

 Clupea humiUs, 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 occuri-ence of the remains of turtles 

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

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

 Trionyx from Church Buttes. 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 liy 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 



