650 THE WASATCH FAUNA. 



Hybacotherium index Cope. 



Report U. S. G. G. Expl. Surv. W. of 100th Mer., G. M. Wheeler, IV, Part II, p. 262. Orohippus index 

 Cope. Systematic Catalogue Vertebrate Eocene New Mexico, 1875, p. 20. Orolherium index Cope. 

 Paleontological Bulletin No. 17, p. 4, 1673. 



Represented by the mandibular ramus with many of the molars in good 

 preservation. These number P. M. 3, M. 3. The last premolar is some- 

 what like the first molar, but has but one posterior tubercle, and adds a cin- 

 gular projection in front of the anterior pair. The first premolar has two 

 roots; 'the second is compressed, and with a broad heel behind. In the 

 molars the anterior tubercles are connected by a cross ridge; the posterior 

 are a little more distinct from each other. The inner anterior tubercle is 

 obtuse but not bifid, and its base is connected with the apex of the poste- 

 rior outer by a diagonal ridge. There is a small median posterior tubercle 

 on the No. 2, and a large heel on the last molar. It supports a conic 

 tubercle, which is connected by sharp ridges with the tubercles preceding 

 it. There is a cingulum on the outer face of the true molars, which does 

 not extend on the base of the tubercle of the posterior pair. 



Measurements. 



M. 



Length of molar series 0.0350 



Length of first premolar 0032 



Length of third premolar 0055 



Width of third premolar 0040 



Length of second molar 0065 



Width of second molar 0045 



Length of last molar 0098 



Depth of ramus at first premolar 0021 



Depth of ramns at second molar 0023 



I took this species from the bed on Bear River, Wyoming, from which 

 were obtained the typical specimens of Bathmodon radiatis, Coryphodon latij)es, 

 and Phenacodus primoevus. It is the typical locality of the Wasatch forma- 

 tion of Hayden. The type specimen having been mislaid, is not now figured. 



PLIOLOPHUS Owen. 



Quarterly Journal of the Geol. Soc, XIV, 1857, p. 66. Orotherium "Marsh" Cope. Ann. Report U. S. 

 Geol. Surv. Terrs., 1872 (73), p. 606. Report U. S. G. G. Expl. Surv. W. 100th Mer., IV, II, p. 

 258: numMarshii? 



This genus differs from Hyracothenum, so far as I am able to ascertain, 

 in only one point. This is in the presence of two tubercles on the heel of 



