INTRODUCTION 



of these resemblances are to be ascribed to actual relationship, and which of 

 them have been independently acquired as the result of a more or less parallel 

 or convergent course of development. 



To a considerable extent this difficulty has been removed by the explora- 

 tions of the last few years. The collections made in the White River and 

 Uinta formations by Messrs. Hatcher and Gidley for the museum of Princeton 

 University, and by Dr. Wortman and Mr. Peterson for the American Museum 

 of Natural History, in New York, have brought together a great number of 

 new and finely preserved fossils, which shed new and welcome light upon the 

 problem. For the opportunity of studying the collections belonging to the 

 American Museum I am indebted to the kindness of Morris K. Jesup, Esq., 

 President, and of Professor H. F. Osborn, and gladly take this opportunity of 

 expressing my cordial thanks to these gentlemen. 



The material to be described in the present paper consists principally of 

 fossils from the Uinta Beds, supplemented by some White River specimens of 

 Lcptomcryx and Hypcrtragiilus, which add in an important way to our knowl- 

 edge of those genera. 



The Uinta is the most ancient of the American Tertiary stages in which 

 the artiodactyls began to play an important role in the life of the times. 

 Indeed, the most striking and characteristic feature of the Uinta fauna, as 

 distinguished from that of the preceding Bridger stage, is in the very marked 

 increase of the artiodactyls in general and of the selenodonts in particular. 

 In the Bridger beds selenodonts are very rare as fossils, and not more than 

 two genera have been described from this horizon, while in the Uinta the 

 selenodonts are individually the most abundant fossils, and not less than nine 

 genera of them may be distinguished. More important than this mere increase 

 in numbers and variety is the fact that the Uinta selenodonts are so obviously 

 ancestral to those of the succeeding White River stage. It is hardly an 

 exaggeration to say that the forerunner of every White River selenodont, 

 except those of Old World origin, may be indicated, with more or less con- 

 fidence, in the Uinta fauna. This addition to the phylogenetic series is of the 

 utmost morphological significance, because of the help which it gives in work- 

 ing out the real taxonomic position of the problematical American families. 

 That the problems cannot even now be solved in all respects is due to the fact 

 that the record of most of the lines breaks off with the Uinta, and cannot yet 

 be traced back into the Bridger in any satisfactory way. This interruption 

 leaves the question regarding the position of certain families to some extent 



