204 The American Geologist. October, 1892 
covered in the br.ain. This organ la}' in the space between the 
su})ra-occipital behind and the parietals post-laterally. How 
much of this it actually occupied it is not possible exactly to de- 
termine. The cavity measures five inches from side to side, but 
if analogy is a safe guide, as it probably is, some of this was oc- 
cupied by the ear- capsules. It is probable that the brain proper 
was limited to the space within the forward projections of the 
parietal plates measuring about two and a half inches. This area 
is well outlined in Dr. Newberrj'^s figures where its boundaries are 
much more clearly marked than in the specimen now described. 
(6.) The Frontal plates, in consequence of their thinness, are 
usually, as in the present case, crushed down so that the brain- 
cavity is almost effaced. But the lateral spaces (ear-capsules) 
being protected by the massive post-orbitals are uninjured. 
(7.) The Post-orhital plate continues the outline of the head 
from the marginal behind to the pre-orbital in front, and the post- 
orbital process forms the hind margin of the orbit. On the upper 
face this plate overlaps the parietal, the frontal and the marginal, 
and is slightly overlapped by the pre-orbital. It ends backward 
in a V)lunt point. As the marginal it folds under and forming a 
forward continuation of the above-mentioned ridge that bounds 
the temporo-masseter fossa protects the ear-capsule and the lateral 
aspect of the brain. This ridge gradually sinks until it is lost or 
is merged in another on the inner surface of the pre-orbital plate. 
The natural strength of this plate due to its weight is largely 
increased by its form which may be seen by comparing the sec- 
tions with the figure of the skull. 
Just behind the post-orbital process, and on the lower face, is a 
small and shallow notch (indicated in the figure) for the reception 
of one of the angles of the sub-orbital plate. 
On its lower and inner margin is a strong, stout and cylindrical 
process an inch and a quarter long which evidently joined by a 
suture some one of the plates that formed the roof of the mouth. 
It slants downward and inward at a low angle (about 15° with the 
horizontal) so as to meet a plate that must in some way have cor- 
responded in position and function to the vomer or the presphenoid 
of a recent fish. But no trace of any such plate remains in the spec- 
imen here described, though the two processes approached at their 
distal ends within half an inch of each other on the median line. 
(8.) The Pre-orhital plate is large and outlines the orbit in 
