1092 The American Naturalist. [December, 
protoconid and paraconid. The slight prominence on the posterior 
edge of the protoconid seen in Figs. 1 and 2, is due to wear by the 
opposing superior tooth. The protoconid is larger than the paraconid. 
The Ramus :—The most striking feature of the jaw is the extreme 
downward projection of its anterior angle or flange, which is about 
equal to the depth of the jaw proper. The flange is deeply concave 
exteriorly, its lateral surface is separated from the anterior by a sharp 
ridge of bone. The mental foramen opens far down, almost on a line 
with the inferior border of the ramus. Near the middle of the jaw, 
and just in front of pm. ;, there is a small foramen directed forward 
and upward. The exterior surface below the molars is convex longi- 
tudinally. The masseteric fossa is deep, and is not enclosed posteriorly. 
The posterior angle is very strong, it is but slightly deflected, and is 
directed outward and backward. The condyle is low, being placed a 
little beneath the line of the alveolar border, it decreases in strength 
from within outward, and its articular surface describes accurately a 
reclining semi-cone. The coronoid process is strong, low and rounded. 
The inner side of the jaw is a nearly plane surface. The dental fora- 
men is situated just back of the sectorial and a little below the middle 
of the jaw. The symphysis is very characteristic, it extends far down 
on the flange, and is greatly expanded superiorly and inferiorly, and 
much constricted medially. The chin was broad and very deep. About 
one-third the distance from the incisive alveolar border to the bottom 
of the anterior angle of the jaw there is a large foramen. 
Eusmilus dakotensis is easily distinguished from Æ, bidentatus, 1, By 
its size, which is about two-fifths greater than that of the European 
species; 2, By the structure of the sectorial, which is without the pos- 
terior cusp seen in bidentatus; 3, By the structure of pm. ,, in this 
tooth—in E. bidentatus the posterior cusp is much smaller than the 
anterior, while in dakotensis these cusps are about equal in size. Com- 
pare Figs. 141 and 142, Filhol’s Phosphorites du Querey, with Figs. 
1 and 2 in the plate accompanying this paper. 
The discovery of Eusmilus in the White River beds is additional 
evidence in favor of referring those deposits to the Oligocene as pro- 
posed by Cope and Scott. 
MEASUREMENTS: 
mm. 
Longitudinal diameter of m. ,, . eRe ohio 23 
Transverse diameter of m.,, . ; ; ‘ $ $ 10.5 
Longitudinal diameter of pm.;, . . ., . . 16 
Transverse diameter of pm. q, ; : j ý ‘ 8 
