238 The American Naturalist. (March, 
the canine and a shorter one between it and premolar two. 
Premolars two, three, and four are strong, well developed teeth, 
they increase regularly in size and are separated by diaste- 
mata. The sectorial is large as compared with molars two 
and three, its antero-posterior diameter being almost double 
that of both these teeth taken together. The. metaconid is 
exceedingly faint, the talon is low and flat and consists of both 
an external and internal cone of which the former alone has 
been subjected to wear. Molar two is quite small, not so large 
as premolar two. Molar three is missing but the alveole 
shows it to have been quite rudimentary and implanted by 
one root only in the slightly rising alveolar border of the jaw. 
The present species appears to be most closely related to 
A. wirsinus Cope and A: haydenii Leidy. From the former it 
is readily distinguished by the nearly uniform depth of the 
jaw, by the much smaller canine and by the relative and 
absolute size of the premolar and tubercular teeth. In A. urs- 
nus according to Cope? the first tubercular considerably 
exceeds in size the fourth premolar, in A. taxoides the fourth 
premolar is twice the size of the first tubercular. From 
haydenii it is at once distinguished by the much less elevated 
posterior portion of the alveolus, by the somewhat less massive 
appearance of the jaw and by the diastemata between the pre 
molars. The following are the more important measurements 
of the type specimen. 
. Mt 
Length of jaw from front of synphysis to middle of con- %1 
yle 
Length of premolar dentition = 
Length of molar dentition | 034 
Antero-posterior diameter of sectorial 012 
Antero-posterior diameter of first tubercular 022 
Antero-posterior diameter of fourth premolar 039 
Depth of ramus below first premolar 040 
Depth of ramus below first tubercular a 
In Plate I, figures 2 and 2* represent the side wee” 
views of the type and show well the more importan 
"See U. S. Geogr. S , G. M. Wheeler, part II, Vol. IV, p. 304, 1877. 
