1 92 S. W. WILLISTON. 



neither upper nor lower temporal fenestra, and probably never 

 had. 



These, it seems to me are legitimate conclusions from the evi- 

 dence now available. But the evidence is yet meager, and all our 

 present views may undergo material modification when more of 

 the early reptiles from the Trias and Permian are known. 



EXPLANATION OF FIGURES. 



ep., epiotic. p'-, premaxilla. 



exo., exoccipital. pof. or//;-., postfrontal. 



fr., frontal. po., or pto., postorbital. 



j., jugal. psq., prosquamosal. 



/. , lachrymal. //. , pterygoid. 



mx.y maxilla. q. , quadrate. 



n. or na., nasal. qj., quadratojugal. 



/. or pa., parietal. so., supraoccipital. 



pf., prefrontal. sq., squamosal. 



In Fig. 4, Procolophon , the determination of the squamosal and prosquamosal is 

 that of Woodward. According to the interpretation of Seeley, Broom and Osborn, 

 sq. is the epiotic, psq. the squamosal. I am under obligations to Prof. Case for per- 

 mission to use his figure of Dimetrodon in advance of publication by him. 



