DOUGLASS: THE TERTIARY OF MONTANA 219 
slender in proportion to the size of the skull. The anterior portion of the zygomatic arch 
as proportionally more like that of I. intermedius. The skull is one fifth broader than in 
the latter between the orbits and one third broader at the post-orbital constriction. Though 
the mandible is nearly one third longer, it is no deeper at the last molar. 
Derrattep DrscripTION AND COMPARISONS. 
Dentition.—No upper incisors are preserved. On each side are alveoli for the 
third incisors, but it does not appear that there were functional first and second in- 
cisors. If there were, they were separated from I* by a diastema, and were not 
crowded like the corresponding lower teeth. ‘The canine was small. Only the root 
is preserved. All] the teeth on the right side anterior to P? are gone and appear to 
have been shed when the animal was young, as the alveoli are more or less nearly 
obliterated. 
> is larger than in I. montanus but it is a simple, one-rooted, laterally compressed 
tooth. The diastema between it and P* is the same. P¥* is about the same in both 
specimens. P#* and P* are longer in the present specimen and P* is wider. As in J. 
montanus the anterior cusps of the molars are higher than the posterior ones. The 
molars have nearly the same antero-posterior diameter in the two species, but in 
P. tenuis the transverse diameter is much greater, and the inner portion of the 
tooth is very narrow. Taking Matthew’s figure of J. thompsoni as a basis for measure- 
ment the teeth of the present specimen are even wider in proportion to the length 
than in that species. The last molar is absent from both sides. 
The snout is very slender as compared with the size of the skull. The skull 
is very broad at the zygomatic arches, but narrows rapidly at their anterior portions 
and just in front of the orbit. The palate is broad behind and narrows gradually almost 
to a point in front. The posterior narial opening is in the plane of the last molars. 
There is a median point at the posterior portion of the palate. Though the skull 
was larger, the depth of the malar portion of the zygomatic arch is about the same 
asin I. montanus. The depression on the face at the anterior root of the arch has 
about the same depth but is smaller, leaving a heavier ridge between that and the 
orbit. The nasals are long and slender and are broadest at the anterior portions. 
The skull is broader on top than in any other specimen of Jctops that I have seen. 
The Mandible. — The greater portion of the left side of the mandible is present. 
The coronoid process and the condyle are gone, and the angle is probably not quite 
complete. 
Portions of the first incisors, canine, and second and third premolars are pre- 
served. <As in J. intermedius and I. major there are no diastemata in the lower jaw. 
