26 MAURICE G. MEHL 
The greatest interest of the specimen probably lies in its mandi- 
bular dentition. Beyond a doubt the larger number of teeth are 
on the splenial bone instead of the dentary. Unfortunately the 
crowns of most of the teeth of the mandible were destroyed in 
the separation of the rami of the skull. One is able nevertheless 
to make out the arrangement of all the teeth except for a short 
distance on the anterior border. This space is well beyond the ter- 
mination of a regular, definitely outlined inner pad of teeth, how- 
ever, and most likely only the outer row is continued forward. 
Judging from the size of the teeth exposed in the outer row, there 
are four teeth hidden in this anterior part of each ramus by the 
matrix of the projecting muzzle. As suggested above, the teeth 
are arranged in two groups, an outer row of sixteen teeth, the pos- 
terior twelve of which are shown, and an inner pad or series. In 
the outer row they apparently do not vary greatly in cross-section. 
As to any variation in height of crown I am unable to say. This 
series, I am confident, comprises the only teeth on the dentary. 
The inner series is arranged in a pattern of regular shape. The out- 
line of this pattern is formed by a band of twenty-five teeth which 
become progressively smaller posteriorly from nearly 3mm. in 
cross-section at the anterior border to 1.5 mm. at the posterior 
side. Within this peripheral band are fifteen irregularly disposed 
teeth. In cross-section these range from 4mm. to 2mm., the 
larger being disposed anteriorly. It is impossible to determine the 
height of the crowns of this inner series but it is certain that some 
of them were higher than the regularly placed peripheral group. 
It is interesting to note that while the teeth of the inner series show 
a circular section midway between the base and the apex, the base 
often shows a polygonal cross-section and here only small inter- 
spaces are left between the teeth. 
In Cope’s description of P. coicodus, the second species of this 
genus, the chief distinguishing features are found in the teeth. 
They have a pointed apex like the grass seed Coix lachroma, while 
those of P. cordatus are obtuse. P. coicodus also has “partially 
pleurodont”’ teeth with a swollen crown on a shanklike base. Case 
suggests that the obtuse tooth of P. cordatus is simply that of P. 
coicodus with the pointed apex worn down and that the two species 
