The Skull of Labidosaurus. 79 
in a short clyindrical rod lying under the proximal posterior end of 
the quadrate and articulating at the extremity with the facet already 
described on the lower part of the inner end of the ‘‘epiotic.” 
This articular arrangement is the normal one of the opisthotie with 
the epiotic in the Stegocephala. Chiefly because of this fact I am 
loath to identify the bone with the quadratojugal, to say nothing of 
the anomalous position of the bone for a quadratojugal. Anteriorly 
the suture separating the paroccipital from the supraoccipital passes 
nearly directly forward to the outer side of the posterior lateral pro- 
jections of the supraoccipitals where the dividing suture turns 
inward. Of the suture separating the prodtics I am less certain, 
though it seems to be quite_apparent in the position I have figured 
it in the drawing. The supraoccipital is a large element, when seen 
from above having a marvelous resemblance to the arch of a dorsal 
vertebra. A small dorsal spine in the middle posteriorly is inter- 
ealated in the angle between the inner ends of the postparietals, but 
there is no sutural attachment. Anteriorly the two sides of the supra- 
occipital diverge in the form of zygapophyses, with an emargination 
between them exposing the cerebral cavity. From the median pos- 
terior spine a ridge runs outwards to each ‘‘zygapophysis.” In 
front of each lateral projection, the prodtic, distinguished suturally, 
descends in a rounded margin to form the optic notch. In front 
of these optic notches there is, on either side, a thin, vertical plate, 
attached either to the protic or basisphenoid below the meeting in the 
middle above, leaving an opening of rather small size between them. 
The upper end of these plates is fractured, but it is very evident that, 
in position, relations, and shape they agree quite with similar bones 
bounding the cerebral cavity in most lizards, a small bone, usually 
lost in the macerated skull, whose homology is not well understood. 
Since their position is in front of the optic nerve it would seem to 
preclude the possibility of their being alisphenoids. These elements 
in the mosasaurs I have identified as orbitosphenoids (see University 
of Kansas Geological Survey, Vol. IV, Pl. xxix, f. 5; Kans. Univ. 
Quarterly, Vol. XT, p. 249), but neither identification is quite satis- 
factory. The upper oblique surface of the pterygoid wings is 
concealed posteriorly by the quadrates. In front of the quadrates, 
