PERISSODACTYLA. 
253 
premolars. The canines are large, divergent, and acute, leaving space 
between them for several small incisors, which are lost from the specimen. 
The symphysis is long and coossified. The first premolar possesses a simple 
crown and a single root; the other molars are two-rooted. The second 
premolar has a low acute heel, and no cusp accessory to the main one; the 
third has a more elevated acute heel, and an accessory anterior cusp. The 
fourth has two posterior cusps, the outer continued forward as a crest, and 
two anterior cusps much larger than the others. In the remaining molars, 
the cusps are subequal; the inner subconical, the outer sending a low 
oblique crest forward and inward. The last molar has a prominent heel. 
A specimen of what I suppose to be the 0. vintanum embraces the 
third, fifth, sixth, and seventh superior molars, the fifth, sixth, and seventh 
inferior molars, and numerous bones of the skeleton. The superior molars 
do not differ in their characters from those of Hyracotlierium. The crown 
supports four principal conic cusps, of which the external are flattened and 
connected at the base. Between the posterior part of each of these and the 
corresponding inner cusp is a low tubercle, which is more or less united 
with the latter. There is a cingular cusp at the anterior base of the anterior 
outer cusp. The third premolar has two approximated outer crests, and an 
internal one with low connecting ridges. The palate is deeply excavated 
as in other Perissodactyla. 
The humerus of this specimen is a slender bone, much more so than 
the femur, and has a smooth oval shaft. The head is large and much 
incurved; it possesses a prominent deltoid ridge and a wide bicipital groove. 
The condylar fossa is entirely perforate. The trochlear character of the 
condyles is well marked, there being an angular internal marginal crest, 
and a rounded one at the other end within the margin. This is the “troch¬ 
lear crest” of the more specialized Mammalia, and it is important to note 
that this is the only genus of the New Mexican fauna in which I have 
observed its presence, although it doubtless exists in the three other genera 
of Perissodactyla here enumerated. The external epicondyle is not prominent. 
The head of the radius is a transverse oval without inferior angle, and, in 
accordance with the humeral condyles, the horizontal section of the articular 
face is an open sigmoid. The distal end of the radius is narrow, confirming 
