262 
PERISSODACTYLA. 
their superior molars and some of those called by the latter name by Dr, 
Leidy. As the teeth last described by Dr. Leidy under the name of Hip- 
posyus probably do not belong to the animal first referred to by him (and 
therefore to be regarded as the type), but to the one afterward named by 
Marsh OroJiippus, I subsequently described similar species under the latter 
head. But no characters have, as yet, been pointed out by which to dis¬ 
tinguish the latter from the genus previously described by Owen, whose 
name I therefore adopt. 
Next to the species of Corypliodon, those of HyracotJierium are most 
abundantly represented by individuals in the Wasatch beds of New 
Mexico, They were doubtless the predominant type of omnivores, and fur¬ 
nished food for the numerous cotemporary Creodonta. The jaws and teeth 
are far more frequently found than the bones of the other parts of the skel¬ 
eton, and, as usual, the rami of the lower jaws are the most numerous. 
The characters observed in the latter indicate, seven species, which ditfer 
very materially in size and proportions, but agree closely in general char¬ 
acters. Tliey may be distinguished as follows: first, by their mandibular 
bones and teeth; and, secondly, by their maxillary teeth. 
Mandibles. 
Largest; last molar, 0“.014 in length; ramus, 0“.020 in depth at the last 
premolar; molars with a produced ledge in front... tapirinum. 
Large; last molar, 0“.012; ramus, 0“.020; ledges not prominent. vasacciense. 
Last molar, 0“.011; first molar, 0“.0087; ramus, G“.0127; second and 
third premolars, 0“.0139 . sylvaticum. 
First molar, 0“.006o; ramus, 0“.0130; second and third premolars, 
0“.0135... angustidens. 
First molar, 0“,0059; ramus,* 0“.0115; second and third premolars, 
0“.0080 . index. 
Superior molars. 
Neither external nor internal cingulum of the crown. . f species. 
Cingula weak, interrupted; a vertical crest between the external lobes, procyoninur.i. 
External and internal cingula present, but the internal weak. angusiidens. 
External and internal cingula very strong; enamel rough, vasacciense. 
Larger; outer cusps flattened.. agile. 
Least species; outer cusps conic and well separated. cuspidaium. 
* The measurement 0“.020 in the Systematic Catalogue of the Vertebrata of the 
Eocene of New Mexico, p. 20, is an error. 
