THE MAMMALIA OK THE UINTA FORMATION. 505 



Part III. 



BY HENRY FAIRFIELD OSBORN. 



THE PERISSODACTYLA. 



It is necessary to open this section with some observations upon the synonymy 

 of the Eocene Perissoclactjda. With the assistance of Prof Marsh, the writer 

 recently examined the types in the Yale College collection, in comparison with those 

 at Princeton. The result shows that the entire nomenclature of these genera is in 

 utter confusion, arising from the attempts which have been made by others to work 

 from the brief descriptions given by Prof. Marsh and without the aid of figures. 

 This confusion extends through all the American and foreign literature which relates 

 to the American Eocene fauna, and invalidates a great deal of otherwise very useful 

 work. 



The synonymy of Helaletes (Marsh) is DUophodon (Scott) and Desmatotherium 

 (Scott). Lophiodon nanus (Marsh) also belongs to this genus. //. latidetis (nobis) 

 must be separated from it. It was originally distinguished from H)jraelujus by the 

 presence of a third lobe on the last lower molar ; this lobe is very small and forms 

 the only distinction between the type and the mandibular dentition of Diloplwdon 

 minusculus. The maxillary dentition is precisely like that of Hyrachyiis, except in 

 point of size and in the presence of two internal lobes upon the thiid and fourth pre- 

 molars. The latter feature was given by us as the generic distinction of Desmato- 

 therium. The dental structure (excepting only the rudimental third lobe) and the 

 tarsal characters remove it entirely from the tapir series, and relate it to Tr/plopus, 

 from which, however, it is probably generically distinct. Colonoceras has precisely 

 the dentition of Hyrachyics agrarini^ Leidy. The rudimental horn cores upon the 

 nasals may serve as a generic distinction, although, in the very limited knowledge 

 we have of the nasals of Ilyrachyus, this character is not altogether satisfactory. 

 Limnoliyus is a nomen nudum, having been applied to a type already preoccupied by 

 PaliP^osyops. Prof. Marsh will apply a new generic name to his L. laticeps. 



The primitive horses arc in much'confusion. Eohippus* (Marsh) is a synonym 



* Am. .lour. Sri. mid Art.s. Nov., 1870, p. 401. 



