338 0. C. Marsh—American Jurassic Mammals. 
along the lower margin. The pter ygoid fossa is deep and wide. 
The coronoid process was large, but its exact form cannot be 
determined. 
The type specimen of the present species is from the Upper 
Jurassic deposits of Wyoming. 
Diplocynodontide. 
A third group of Jurassic Mammals is known at present 
from three genera, which have been found only in this country. 
The most typical form, Dplocynodon, is represented on Plate 
X, figure 3, by the specimen first described. This fossil indi- 
cates one of the largest mammals yet found in the Jurassic. 
In this genus, there were at least three lower incisors, directed 
well forward. The canine is very large, elevated, and trench- 
ant, and inserted by two strong fangs. Behind this, there are 
twelve teeth, all essentially of the same type, so that, from the 
outer side alone, it is difficult, if not impossible, to distinguish 
the premolars from the molars. The crowns of these teeth are 
composed of a main external cone, with a small, elevated lobe - 
in front, and a lower one behind. This is repeated on a re- 
duced scale on the inner side, except that the posterior cusp is 
rudimentary, or wanting. The antero-posterior faces of the 
crowns are deeply excavated, and grooved. 
The jaw is elongate, and eently curved below. The coronoid 
process'is large, and elevated. The condyle is placed very low, 
nearly on a line with the teeth. The angle of the jaw is pro- 
duced into a distinct process (d), the lower mar ein of which 
bends outwards, although the process as a whole has a slight 
inward direction. 
In Diplocynodon victor, the mental foramen is beneath the 
interspace between the second and third premolars. The dental 
foramen is large, and is situated intermediate between the last 
molar and the angle of the jaw. From its front margin, the 
narrow straight mylohyoid groove extends forward, nearly ~ 
parallel with ‘the lower mar gin of the ramus. 
An upper jaw referred to this species contains the canine and 
eight succeeding teeth in excellent preservation. The canine 
is very large, and has two distinct fangs. The molar teeth 
have one, main, external cone, and two lateral cusps, which rise 
from a strong basal ridge. On the inner side, there is one main 
cone, with a ‘small posterior heel. The outer face and the sides 
of the upper molars are deeply sculptured with irregular 
grooves. 
The European genus Amphithervwm may possibly belong to 
this family, but the lower canine has only a single root, and 
the molars appear quite different from those of the American 
forms. 
