MESODONTA. 
145 
One of these is a portion of the mandibular ramns with a single perfect 
molar; another individual is known from an isolated molar. The former 
displays the characters of the larger species, viz, a crown narrowed in 
front, where it supports three approximated cusps, and widened behind, 
where an elevated border embraces a basin-shaped concavity. In this 
species, the anterior cusps are well defined and subequal in size, and the 
posterior angles of the posterior concavity each support a cusp. The outer 
posterior cusp is connected by a strong oblique ridge with the posterior 
of the two anterior inner cusps. A well-marked cingulum surrounds the 
external basis of the crown, and extends round its front nearly to the 
anterior inner cusp. Enamel smooth. 
Measurements. 
M. 
Length of the crown of the molar.. 0. 0034 
Width of the same. .. . 0. 0027 
Depth of the ramus at the same... 0. 0005 
Thickness of tbe same... 0. 0030 
As already observed, this species may be referrible to Microsyops. 
PANTOLESTES, Cope. 
Proceed. Amer. Pliilos. Soc,, 1872, p. 407 [separata August 30). 
The type of this genus resembles, in structural characters of the 
dentition of the lower jaw, the Hyopsodus and Sarcolemur, already known in 
the collections of the different explorations of the Kocky Mountain lake- 
basins. While it possesses the normal number of molar teeth belonging to 
these, it preserves a sectorial character of the premolars more posteriorly 
then in any of the allied genera. The typical specimen of the P. cliacensis 
presents four premolar and three molar teeth; the fourth premolar alone 
remaining with the three true molars. The premolars are all two-rooted, 
except perhaps the first. The fourth is a simple, flattened, triangular cusp, 
with a small tubercle at the base behind, wanting the inner cusp of other 
genera. The molars exhibit the usual four cusps, the external crescentoid, 
the inner discoid in section, excepting the inner anterior, which is double, 
an anterior twin cusp of smaller size being closely united with it. The last 
molar has a distinct fifth tubercle, or heel. 
10 G E 
