744 S. W. WILLISTON 
below and a greater mobility, or streptostyly, of the quadrate. 
Our specimens show a loose union of the squamosal with the 
quadrate, and it was the absence of the squamosal and postorbital 
in one specimen which induced me at first to believe that the whole 
temporal region was open. It is very possible that a like condition 
existed in Varanosaurus and that it may eventually be found to 
have a superior temporal vacuity only. I hope to decide this point 
by a study of additional material later. 
I cannot be sure of the differentiation of the elements of the 
slender parietal arch, but I think it is very probable that it is formed 
Fic. 1.—Araeoscelis gracilis Williston. A, skull, from above; B, the same from 
the side, both % natural size; fr, frontal; j, jugal; m, maxilla; , nasal; p, pre- 
frontal; pa, parietal; pf, postfrontal; po, postorbital; pp, supraoccipital and parocci- 
pital; g, quadrate; sg, squamosal; ¢, tabulare. 
more or less by the tabulare, as in the Lacertilia. The exclusion 
of the postorbital from the orbit seemed almost incredible, but I 
am convinced that such was the case in Araeoscelis by the agree- 
ment of several specimens. This exclusion would seem to mean 
that the single bone found here in the Lacertilia and Mosasauria 
is really the fused two bones, the postfronto-orbital. 
Whether or not Araeoscelis was phylogenetically related to the 
Squamata scarcely a doubt can remain that the single arch in lizards 
was the result of the progressive loss from below of the squamosal, 
and not the loss of the lower arcade in some rhynchocephalian 
reptile, as has been generally believed. The Squamata undoubt- 
edly arose from just such a type of skull as is shown in Araeoscelis. 
