178 S. W. WILLISTON. 



Diapsida. " Large supra- and laterotemporal fenestrae ; latero- 

 temporal fenestra sometimes secondarily closed. Bony elements 

 of arch widely separated. Lower arch tending to degenerate 

 first. 



" Squamosals and prosquamosals often reduced, more generally 

 separate, partially covering or withdrawn from the quadrate." 



The closed or nonfenestrate condition of the temporal region 

 has long been recognized as a primitive character in the reptilian 

 skull. Cope, Baur and Seeley, and other authoritative writers 

 have repeatedly called attention to the striking resemblances in 

 the arrangement of the bones forming this region in some of the 

 early reptiles and the Stegocephalia. Largely because of this 

 resemblance some authors have urged the reptilian nature of the 

 Stegocephalia, either uniting them with the reptiles as a branchiate 

 division of the class, or placing them in a distinctive class, as 

 " Proreptilia." 



While these elements are so nearly alike in the stegocephs and 

 cotylosaurs as to leave no doubt of their homologies, in the 

 higher or more specialized reptiles the changes have been so 

 great that the identification of some of the bones is doubtful. 

 As a result of this uncertainty, many names have been proposed 

 for the different temporal elements, aside from the postfrontal, 

 postorbital and jugal, about which there has been no doubt or 

 dispute. For the other four bones, however, I find the following 

 names in use within recent years : epiotic, os tabulare, paroccip- 

 ital plate, squamosal, prosquamosal, suprasquamosal, supratem- 

 poral, mastoid, supramastoid, supraquadrate, paraquadrate, zygo- 

 matic, quadratojugal, squamosal I., squamosal II. At the present 

 time, the terms squamosal, prosquamosal, quadratojugal and 

 epiotic seem to have most acceptance, though supratemporal is 

 largely used for prosquamosal. 



The temporal bones in the Stegocephalia and Cotylosauria 

 are practically identical in number and arrangement (Figs, i, 1 1). 

 In -both these forms it will be observed that the squamosal artic- 

 ulates broadly in front with the postorbital or postfrontal ; on the 

 inner side with the parietal ; on the outer side with the prosqua- 

 mosal, and sometimes the jugal. The prosquamosal unites 

 broadly in front with the jugal ; on the outer side with the 



