OLIGOTOMUS, Cope. 



Ann. Rep. U. S. Geol. Survey of the Terrs., 1872, p. 607. 



" Molars constructed much as in Hyopsodus and Lophiothc- 

 rinm, viz., with two external subtrihedral cusps which wear 

 into crescents, the posterior connected by a low oblique ridge 

 with the basis- of the anterior cone of the inner side ; the 

 latter with two conic cusps. It differs from these genera and 

 from Orotherium in the possession of two premolars ; the in- 

 ferior molars are probably six, leaving four true molars." 



OLIGOTOMUS CINCTUS, Cope. 



Loc. cit. 



Represented in our collection by the penultimate lower 

 molar, and a caudal vertebra, which has a remarkably long, 

 slender, and simple centrum, with rudimentary metapophyses 



OPISTHOTOMUS, Cope. 



Wheeler's Survey, Pal. v. iv., pt. n, p. 152. 



" The inferior lower molars do not display a bifid or double 

 anterior cusp ; and the crowns exhibit two anterior cones, and 

 an inner cone and outer crescent posteriorly. The posterior 

 crescent is well defined, and is continued on a narrow crest 

 to the anterior inner tubercle. The posterior molar presents 

 the peculiarity of a series of three cusps in one line, the me- 

 dian having another or lateral cusp near it." 



This genus has hitherto been found only in the Wahsatch 

 formation ; but we have discovered it to be represented in the 

 Bridger series by the species O. astutus, Cope. Our specimen 

 consists of a part of the ramus mandibuli containing a single 

 molar tooth. 



