218 O. C. Marsh—New Tertiary Mammals. 
Helaletes boops, gen. et sp. nov. 
Among the Tapiroid mammals in the Green River Tertiary 
deposits, there are two distinct genera which have been referred 
to Lophiodon. Dr. Leidy has given the name Hyrachyus to one 
of these, which embraces the larger species, and the other may 
be called Helaletes. In this genus the last lower molar has a 
third, posterior lobe. The upper molars resemble those of Lo- 
phiodon. The astragalus differs widely from the Tapiroid type, 
and in its narrow oblique condyles is very similar to that of the 
Equide. Other characters of the genus will be given in the 
full description. 
The present species is based upon the greater portion of a skull 
with teeth, and the more important parts of the skeleton of the 
same individual. The teeth agree in size with those of Lophio- 
don nanus Marsh, but the last upper molar has a small tubercle 
on the outer margin between the cusps, which appears to be 
wanting in the type specimen of the latter species. There are 
also other differences of importance. Both species doubtless 
belong to the same genus. 
Measurements. 
Longitudinal extent of last three lower molars,.......--- 33°57, 
Antero-posterior diameter of last lower molar,.......- itnlkae 
Depth of jaw below last lower molar,............2.0+¢0% 4 
Antero-posterior diameter of last upper molar,........--- 111 
SYRUOVETHO: TIMINOLOE FS re ee OA ek 11°5 
deny tls OF MERRINE eee Glatvieae ere 
Width between condylar ridges,....... Seca eens avs nee) 2% 
The type specimen of this species was discovered, last au- 
tumn, at Grizzly Buttes, Wyoming, by Mr. G. G. Lobdell, Jr. 
Part IV. 
Paramys robustus, sp. nov. 
A new rodent, with lower molar teeth similar to those : 
Paramys, but a much larger animal than the known i sige 
Antero-posterior diameter of last lower molar,......-- ee sor 
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