O. C. Marsh— American Jurassic Mammals. 331 
Allodon fortis, sp. nov. 
The present species appears to be generically identical with 
the type specimen of A//odon laticeps, but is represented by re- 
mains of much larger size. The premaxillary shown on Plate 
VII, figures 7-10, may be taken as the type specimen. A num- 
ber of upper molar teeth, and the large lower incisor (figures 
14 and 15, of the same Plate), are also referred to this species. 
The first incisor in this premaxillary was very small, and sit- 
uated close to the median line. It is wanting in the present 
specimen, but its size and position are indicated in the above 
figures. The second incisor is large and prominent, and is the 
principal front tooth. It has a distinct crown, which is covered 
with enamel, and consists of one large main cusp, with a small 
posterior cone. The lower surface is much worn, evidently by 
an opposing lower tooth which bore directly against it, from 
its apex to the small posterior prominence. The sides of the 
crowns show no signs of wear. The third and last incisor is 
much smaller, and is separated from the second by a short 
diastema. It has a distinct crown covered with enamel, but 
shows no marks of attrition. It is situated a little in advance 
of the suture with the maxillary, shown in figure 7, s, Plate 
VIL. 
A second specimen referred to this species is shown in figures 
11-13, Plate VII. It is a portion of a left upper jaw con- 
taining three premolars, apparently the first, second, and third. 
The first two of these have a single external cone, and two 
inner cones, and the second tooth is larger than the first. The 
third premolar is still larger, unlike the corresponding tooth in 
Allodon laticeps, and has a second exterior cone behind the 
main one. Above this tooth, there is a large cavity, appar- 
ently the entrance of the antorbital foramen. This is shown 
in figure 11, 7, Plate VII. 
The large lower incisor which met the prominent one above 
is probably represented in figures 14 and 15. This tooth is 
faced with enamel in front, and grew from a persistent pulp, 
like the incisor of a rodent. The summit is incomplete, and 
hence, the shape of the worn surface cannot be determined. 
The specimens here described indicate that Adlodon fortis 
was the largest mammal of this group hitherto discovered in 
the Jurassic. In bulk, it was three or four times as large as 
Allodon laticeps, and about the size of a rat. 
The only known remains of this species are from the 
Atlantosaurus beds of the Upper Jurassic, in Wyoming. 
