THE SKULL OF PALEORHINUS 133 
the quadrate above and behind the quadrate foramen. It has a 
height of three-fourths inch, with a maximum width of five-eighths 
inch, at its lower, open end. 
Otic capsule-——The ear opening is about the same size as the 
quadrate foramen and lies almost directly above it and separated 
from it by seven-eighths inch of bone. It is irregularly oval in out- 
line with a height of seven-eighths inch and a width of five-eighths 
inch. The axes of this opening, and of the small notch which lies 
below and slightly behind it, le in the same line, and the two open- 
ings are <9 close together that their margins are confluent. 
Within the skull the ear cavity enlarges slightly and extends 
inward to a depth of seven-eighths of an inch. At the bottom of this 
subspherical cavity a smaller opening three-eighths by one-fourth 
inch leads into the cranium through the large cavity between the roof 
and the floor of the skull. The angle at which the ear opening enters 
the skull is about 55° from the median line of the skull, similar to that 
formed by the posterior end of the supratemporal vacuity. 
So far as can be ascertained this is the first time this opening has 
been figured and described. Fraas does not show it in his illustrations 
of Belodon kapffi and Mystriosuchus planirostris, nor does Cope 
figure it in his illustrations of Belodon buccros. Von Meyer in his 
illustrations of Belodon kapffi shows an opening in the skull which at 
first sight appears to correspond with this one, but on further exam- 
ination it proves to be the posttemporal fossa. Neither is the open- 
ing shown on McGregor’s excellent illustrations of Mystriosuchus 
planirostris and other forms, given in his recent paper on the Phyto- 
sauria. 
THE UNDER SURFACE OF THE SKULL 
This surface presents, in general view, a long triangular depres- 
sion which extends from the anterior portion of the snout backward 
as far as the basipterygoid processes of the basisphenoid. This 
depression is very narrow where contained by the premaxille, but 
widens gradually in the posterior part of these bones and behind them, 
until it attains its greatest width opposite the anterior portion of the 
transverse bones. It is bounded laterally by the premaxille and 
maxilla, postero-laterally by the transverse bones and _ posteriorly 
by the short, transverse, wedge-like processes of the pterygoids and 
