rEEISSODACTYLA. 
263 
It is evident from the above tables that I am not certainly acquainted 
with the superior molars of H. tajpirimim, H. index, and H. sylvaticmn, nor, 
with the mandibular teeth of H. xorocyoninum and H. cuspidatim. I have 
however, numerous teeth, which are not associated with those of the oppos¬ 
ing series, and which doubtless cover nearly the entire ground of compari¬ 
sons. 
It would have been desirable to have compared specimens of these 
species with the types of those described by Professor Marsh, which belong 
presumably to Hyracotherium. But I have been precluded from access to 
his collections by circumstances beyond my control. On application to 
Professor Leidy for similar facilities with his own types, permission was 
granted, with the accompanying information that the larger portion had been 
lent to Professor Marsh, so that they also have been inaccessible to me. 
Hyracotherium tapirinum, Cope. 
Plate Ixvi, figs. 12-16. 
Orohippus tapirinus, Cope, System. Cat. Vert. Eocene New Mexico, U. S. Geog. Survs. 
W. of 100th M., 1875, p. 20. 
Represented by mandibles with teeth, of five individuals, which exceed 
in size those of the species heretofore known, being larger than the smaller 
Hyrachyi. The opposite cusps of the molars are not separated by so deep 
a notch as in some of the other species, while the oblique ridges extending 
forward from the outer tubercles are well developed; the same is true of 
the ridge which extends from the prominent heel of the last molar. The 
anterior ledge is horizontal, and is bounded by a ridge which descends from 
the anterior external tubercle and becomes transverse. It is less marked in 
all the other species. Enamel nearly smooth. The external cingulum is 
very faint on the last molar, but becomes more distinct on the anterior 
molars; none on the inner side. 
Measurements. 
M. 
Length of the bases of the last two molars (No. 1). 0. 025 
Length of the basis of the penultimate molar. 0. 011 
Width of the basis of the penultimate molar.......... ... 0. 008 
Depth of the jaw at the penultimate molar. 0.022 
Depth of the jaw at the last premolar (No. 2). 0. 020 
