The Skull of Labidosaurus. 81 
diately back of the orbits. They also form a part of the lower 
margin of the mandible, visible from below as far back as the middle 
of the orbits, having between them and the hinder end of the dentary, 
an elongate and acute projection of the angular. The suture between 
the angular and the articular continues the curve of the inner border 
of the mandible to the outer side of the extreme posterior end of the 
angular process. The suture between the angular and the surangular 
passes forward nearly midway of the mandible, and nearly parallel 
with the upper border in the closed jaws, to the hind end of the 
dentary, that is to nearly opposite the posterior end of the orbits. 
The thin ascending plate of the surangular reaches at the summit 
nearly as high as the lower margin of the orbits on the inner side 
of the temporal roof. Over the summit the slender posterior end 
of the coronoid is visible in the closed jaws, but its anterior part is 
concealed by the transverse bones. The articular is a short bone, 
turned inward, with a thin inner margin. It is apparently continued 
forward as a slender prolongation above the margin of the splenial 
or angular and forming the lower border of the mandibular cavity, 
to a slender, acute point nearly as far as the hind end of the mandibu- 
lar tooth series. Whether or not it is separated from the articular 
as a distinct bone, the prearticular, or indeed of its precise relations 
I will not be sure. Sixteen teeth I count in the mandibular series 
in three different skulls. They resemble the maxillary teeth, but are 
somewhat smaller. The first or second is distinctly larger than the 
following ones. : 
A minute comparison of the skull of Labidosaurus with that of 
Procolophon or Pareiasaurus would be most interesting and instruc- 
tive, but since this is impossible for me to make I trust that the 
figures and descriptions herewith given may furnish the basis for 
such a comparison by others. With the exception of the form 
described by Broili (Seymouria), I believe that we have no positive 
assurance of the simultaneous possession of all four roof-bones, 
supraoccipital, epiotic, squamosal and prosquamosal in any coty- 
losaurian, using the term in its broadest sense. That all these four 
elements should occur concurrently in the primitive reptiles is of 
course to be expected, and Broili’s genus seems to furnish an example. 
