138 
MESODONTA. 
thick inferior border, regularly convex from side to side. Masseteric ridge 
prominent. 
The last molar is wanting in the next specimen, only the first and 
second true molars remaining. In the first, the two anterior interior cusps 
are low and well separated. The anterior exterior cusp is larger, and is 
approximated to them iri position. It is connected with the anterior 
interior cusp by a curved ridge, which forms the anterior border of the 
crown, and with the posterior of the two, by a yoke directed slightly 
backward, whose superior margin is emarginate between the cusps. The 
posterior part of the crown is wider than the anterior, and consists of a 
basin-shaped concavity surrounded by an acute, raised margin, which rises 
into a large subtrihedral cusp at the posterior exterior border, and a smaller 
angular elevation at the posterior interior position. The ridge bounding 
this basin reaches the posterior of the two anterior interior cusps; its external 
line curving inward to the base of the cusp. The same description applies to 
the second true molar, excepting that the two anterior interior cusps are 
closely approximated, and that the cusps of the external side are less 
elevated. It is also slightly larger than the second. The enamel of both 
teeth is of glassy smoothness, and the base of the crown is marked on the 
external side only by a continuous cingulum. 
A 
Measurements. 
M. 
Depth of the mandibular ramus of No. 1 at the anterior part of the last molar 
tooth... . . 0.015 
Thickness of the same at the anterior part of the last molar tooth. 0.008 
Length of the last molar tooth... 0. 007 
Width of the same in front.. ... 0.0045 
Width of the second molar behind.■- 0.0050 
Width of the*econd molar of No. 2 behind. 0.0055 
Width of the same in front. 0.0045 
Length of the same.... 0.0005 
Length of the first molar of No. 2. .. 0. 0003 
Width of the same in front. 0.0040 
Width of the same behind. 0. 0054 
Elevation of the crown of the same at anterior interior cusps. 0.040 
Among the bones which accompanied this specimen were a few teeth 
of Hyracotherium. I cannot trace any of the bones to this genus, however, 
