344 
A MEMOIR UPON THE GENUS 
of the teeth than in the larger species of Palceosyops. In the last molar a 
very rudimentary hypocone is present. The position of this cone certainly 
corresponds with the large hypocone found in Limtiohyops laticeps, and I believe it 
is placed too far internally to be a metaconule. The posterior internal cingulum of 
the last molar bordering the metaconule is large but is distinctly separated from it, 
and extends along the posterior border of the tooth as far as the external lobes. 
Lower jaw. — The alveolus for the lower canine is as large as that for the upper, 
so that probably these teeth were equal in size, as in P. pahidosus. The post 
canine diastema is quite large and the diastema between premolar 1 and 2 
is very .small. The first inferior premolar has a well developed heel and 
a slight indication of an anterior tubercle. The protoconid of the second preniolar 
is unusually large and prominent ; it is very much higher than any of the other cones 
of the following premolars. In the third premolar the V’s are not well expres.sed; 
the anterior crests of the anterior lobes are large but run nearly directly forward. 
In the posterior V of this tooth neither the anterior or posterior limb is well 
marked. The last premolar differs from the one just described in having strongly 
marked double V’s, both of which are well developed and have their anterior and 
posterior crests high and continuous. As in all the species of this subfamily the 
entoconid of the last premolar is wanting, but the crest running to it in this species 
is large, and shows a decided advance in structure over the condition of this tooth 
in P. paludostis. All the premolars of this species have traces of an external cingu- 
lum, and in the last two an anterior and posterior cingulum are well seen. All the 
cones of the inferior true molars are very high and sharp, the external and median 
valleys separating the latter being very deep. The posterior tubercle of the last 
inferior molar is large ; its vertical height is equal to that of the anterior lohes 
of the molar. The .size of the incisor alveolus which is preserved in a jaw in the 
collection, indicates that the inferior median incisor was the largest of the three ; the 
external, judging from the size of its alveolus, being very .small or indeed rudi- 
mentary. 
Skidl, (PI. X, fig. .3). — The facial region of the skull of T. adtridens 
has been figured by Scott and Osborn in their report of 1877. This speci- 
men contains also the greater jaart of the lower jaw, bearing the teeth. 
There is one other fragment of a skull belonging to this genus in the 
collection, which from its large size seems to belong to T. validus. Owing to 
the lack of material and the damaged condition of the specimen, it is 
impossible to give the exact dorsal contour of the skull, although the parts 
preserved indicate that the facial region was very high and strongly com- 
pressed. The posterior part of the malar insertion is flat and elongated. Two 
fragments of the roof of the skull belonging to a specimen of this species in the col- 
lection indicate that the posterior narial and interorbital regions were flat and rather 
narrow. There is no frontal depression in the skull of T. adtrideiis like that of 
