DOUGLASS: THE TERTIARY OF MONTANA OA 
this place. The inferior dental series is 32 per cent. (nearly $) larger than that of 
I. intermedius and 10 per cent. larger than I. tenwis. 
DENTITION. 
Superior Dentition. —The width of P* is about two-thirds its length. In I 
fenuis it is about one-half. The posterior cusp is more distinct from the protocone 
than in J. montanus. There is a cingulum on the posterior outer portion of the tooth. 
P+ has a low and minute but distinct anterior basal cusp, and a strong cingulum 
on the posterior outer portion. The protocone is a little higher than the cusp be- 
hind it. Both are lens-shaped in section and rather blunt pointed as seen from the 
side. The tooth has minute traces of anterior and posterior intermediate cusps. 
The posterior interior cusp appears as a cingulum-like ledge. 
The molars have distinct cingula on the outside tending to form anterior and 
posterior outer basal cusps, except on the posterior of M#. ‘There is a minute cin- 
gulum on the anterior portion of the inner cusp in M+ and the posterior inner cusp 
is small but well developed. M®* has also an anterior cingulum but the posterior 
cusp is smaller than on M+. M® is smaller than the other molars and its posterior 
outer cusp (metacone) is minute. It has a trace of the posterior inner cusp. 
Inferior Dentition. — The first incisor is wanting. The other incisors and the 
canine are arranged in an antero-posterior row in line with the premolars and 
molars. I, and I; are spatulate, not much unlike the lower incisors of modern 
ruminants. Is is larger than I. 
The canine has a higher crown than the incisors, but is narrow toward the top, 
instead of expanding like the incisors. 
‘P+ is one-rooted and it inclines forward, but less so than the canine. 
Ps is two-rooted and has a small heel. The protoconid is quite high and nearly 
erect. 
P has anterior and posterior cusps on the protoconid of nearly equal size and 
height, and a minute basal heel. 
On P, the anterior cusp is larger than on Pg. The outer principal cusp is larger 
and higher than the inner one. On the heel the outer cusp is higher and larger 
than the inner one, and this in turn is larger than the median one. 
M,; differs from Pz in having the anterior cusp higher and more confluent with 
the two principal cusps which are more nearly equal in size and height and are 
flatter behind, in the outer cusps of the heel being more nearly even, and in the 
median posterior cusp being larger. On Mg the posterior cusp on the heel is higher 
than the other two. 
