"Molars constructed much as in Hyopsodus and Lophiotherium, 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 inferior 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. 11, 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 median 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.