O. C. Marsh—American Jurassic Mammals. 335 
front backward. The canine is inserted by two fangs, more or 
less distinct, and in most forms, its crown is prominent and 
trenchant. Three or four premolars follow, increasing in size 
backward, with the last usually very prominent, and in some 
forms, larger than the canine. These premolars all have two 
roots, and a compressed crown. All have one main cusp, and 
a small posterior heel. There is usually a small anterior cusp, 
especially on the posterior teeth. 
The molar teeth are from six to eight in number, and are 
essentially identical in form, and usually distinct from the pre- 
molars. The crown consists of one main external cone, high 
and pointed, and three internal cusps, which vary much in 
development in the different genera. Seen from the outside, 
these teeth appear to be inserted by a single fang, but, in most 
cases, each has two roots, although these are nearly or quite 
connate. When the jaw is embedded in the matrix, and the 
diminutive teeth uncovered as far as safety will permit, the 
features of one side only of thé molars can be determined. 
Thus in figure 1, Plate LX, the outer exposed side of one lower 
jaw (Stylacodon) is shown, while in figure 2, the inner side of 
another, jaw (Drvyolestes) is represented. In figures 3 and 4, 
the two sides of the same jaw are placed together, and the 
main characters of the lower molar teeth of Dryo/estes are thus 
made evident. . 
There are seven superior molars, and these have one main 
inner cone, and three outside cusps that vary in size and pro- 
portions in the different genera. 
DRYOLESTES AND STYLACODON, 
The two genera most nearly allied in dentition are Dryolestes 
and Stylacodon, typical examples of which are shown on Plate 
IX. The number of lower teeth in the best preserved speci- 
mens appears to be the same in each, while the incisors, canine, 
and four premolars, show no marked differences. In Dryo- 
lestes, the eight molars which follow are all of one type, and 
differ but little except in size. Al] have the inner middle cone 
of the crown as high as, or higher than the outer main cone. In 
Stylacodon, the first two of these teeth resemble the anterior 
premolars in shape, and like them show from the outside 
double fangs. The main external cone is quite as high as the 
Opposite cusp. 
In Dryolestes, moreover, the lower jaw is comparatively 
short and massive, deep below the molar teeth, with its lower 
margin strongly convex. The condyle in the best preserved 
specimen is concave transversely, and has its lower margin 
nearly on a line with the summits of the molar teeth. 
