150 
MESODONTA. 
abruptly. The enamel is smooth, and the ciugiilum is represented by a trace 
between the bases of the external tubercles. 
Measurements. 
Leugth of the second triie molar... 
Width of the same posteriorly.. 
Elevation at same point. 
Transverse diameter of the ramus... 
HYOPSODUS, Leidy. 
Leidj^, Keport Geol. Surv, Terrs,, i, p. 75. 
In this genus, the cusps of the true molars are all elevated and siiiiple, 
and the last premolar presents an internal cusp. According to Leidy, there 
are three incisors, which are in immediate contact with the canine, as the 
latter is with the premolars. Hyopsodus has been regarded by Leidy as a 
“ Pachyderm ”, as was done by Cuvier in the case of the allied iovm. Adapts. 
As observed by Leidy, the American genus nearly resembles the European 
(under the synonym Aplielotlierium). As the latter is believed by Gaudry 
and Gervais to be Lemuroid in affinity, Ilyopsodus must have a similar 
reference. This is confirmed by the approximation in dentition to Tomithe- 
rium through intermediate genera. 
The type is H. patdiis, Leidy; a second species is H. vicarius, Cope, 
both from the Bridger beds of Wyoming. A single jaw-fragment from 
New Mexico, was referred by me in the “Systematic Catalogue” to the 
former, but the material is insufficient for final determination. 
Hyopsodus miticulus, Cope. 
Plate xlv, figs. 10-12. 
Ilyopsodus miticulus.. Cope, System. Cat. Vert. New Mexico, U. S. Geog. Survs. W. of 
100th M., 1875, p. 18. 
Esthonyx miticulus., Cope, Report Vert. Foss. New Mexico, U. S. Geog. Survs. W. of 
lOOtli M., 1874, p. 8; Id., Ann. Report U. S. Geog. Survs. W. of 100th M., 1874, 
p. 120. 
Parts of several specimens of this species show that the molars are 
similar in size to the II. patdus, but that if has a much smaller last inferior 
molar, which has such a low heel as to resemble the corresponding tooth of 
the species of Esthonyx. The last two premolars are more robust than in 
II. paidus, and possess ludimental anterior basal tubercles, of which a trace 
M. 
0. 0080 
0. 0075 
0. 0040 
0. 0080 
