MESODONTA. 
151 
only exists in the li. paulus. The mandibular ramus is considerably shal¬ 
lower, and the species was probably more diminutive. 
Represented by portions of mandibular rami of three or four individuals 
of the same size as those referred to some of the species above described. 
There are represented two premolars and three molars; other teeth are 
lost. The molars differ from those of the tlwee preceding species in lacking 
the notch or groove dividing the inner anterior cusp of the crown, giving 
the worn surface a more simply sigmoid form; the anterior portion is, more¬ 
over, not materially more elevated than the posterior. The last molar has a 
large heel, an inner and two anterior tubercles when little worn. The pre¬ 
molars preserved are each two-rooted, and the penultimate is without heel 
or inner tubercles. 
Measurements. 
M. 
Length of the three true molars (No. 1). 0.0120 
Length of the two last premolars (No. 2). 0. 0064 
Length of the first true molar (No. 1) .. 0. 0040 
Width of the first true molar (No. 1). 0. 0030 
Depth of the ramus at first true molar (No. 1). 0. 0080 
The worn surfaces of the first and second true molars are much like 
those of the corresponding teeth of Menotherimi, Cope, That genus differs 
in the reduced form of the last inferior molar and in the premolars. 
OPISTHOTOMUS, Cope. 
Cope, System. Cat. Vert. Eocene New Mexico, E. S. Geog. Survs. W. of 100th M,, 1875, 
p. 15. 
Represented by inferior molar teeth of two species. These do not dis¬ 
play a bifid or double anterior interior 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 is also probably Mesodont, but differs widely in the form 
of the last molar from Tomitherium^ Pantolestes, &c. This tooth would 
appear by its form to be capable of a sectorial function in relation with the 
opposing tooth of the superior series. 
