INTRODUCTORY. 



The study of two genera oi the Dinocerata forms the first of a series of 

 Palaeontological Memoirs that will be published by the E. M. Museum of Prince- 

 ton College. 



The Museum already contains a very interesting collection of Tertiary 

 fossils, chiefly procured by parties going out from the college. The first of 

 these field-parties was formed in the summer of 1877. After four weeks in 

 Colorado they camped for the remainder of the season in the country lying near 

 Fort Bridger, Wyoming Ter. In 1878 a second party, smaller but better 

 equipped for collecting fossils, returned to the same field, extending their jour- 

 ney into the Loxolophodon beds of the Bitter Creek country, and making their 

 way back to Twin Buttes, and thence to Fort Bridger, after a short trip up 

 Ham's Fork. During both seasons the principal collections were made in the 

 Bridger Beds (Upper Eocene), so that the fauna of this group is finely repre- 

 sented in the Museum. 



In the first Bulletin the collections made during the summer of 1877 

 were described. The writers there stated that they were fully aware they 

 were upon ground already quite familiar to science. The same thought 

 occurs in some measure in connection with this Memoir. Two distinguished 

 palaeontologists in this country, with large collections at their command, 

 have been contributing to a general knowledge of the Bridger fauna for years. 

 But many features that have not been brought to light are discovered 

 among our collections, so these studies are offered, in the belief that they con- 

 tain much that is original. At the outset, the writer acknowledges with 

 pleasure his indebtedness to the works of these authors, to whom full credit 

 is accorded in the text 



The horizon of the genera whicli are the subject of the present Memoir is 

 the Bridger group. Upper Eocene. They had quite an extensive range in the 

 Tertiary basin in which these beds were formed, and were the largest in size of 

 the many varieties of animals which roamed on the borders of the great Eocene 

 lakes. The sub-order of Dinocerata is of more interest from a consideration of 

 the many varieties which it includes than from a phylogenetic point of view ; 

 for its genera possess many characters by which we must consider them as form- 



