1^6 S. W. WILLISTON. 



if the differences of these reptiles are sufficiently great to separate 

 them into distinct orders, it would seem proper to distinguish the 

 Cotylosauria from both the Synapsida and the Diapsida. In- 

 deed Professor Osborn himself excludes them from union with 

 either group in some of his definitions. 



Furthermore, I cannot accept the conclusion as definitely 

 proven, or even probable, that the reptiles are really diphyletic. 

 The turtles seem, with much reason, to have had an independent 

 origin from the cotylosaurs. My views in general of the pylo- 

 genetic relations of the orders of reptiles are pretty well expressed 

 in the following diagram published by Cope in I896. 1 It will be 



Pterosauria. 

 \ 



Dinosauria Mammalia 



\ Squamata 2 



\ / 



Crocodilia 







Rhynchocephalia 



\ 



\ . - 



\ Theriodontia 



Sauropterygia 



/Anomodontia 



Ichthyosauria 



Testudinata 



\ N 



N - 



Cotylosauria 



seen that, with the exception of the Ichthyosauria and Testudi- 

 nata, the phylogeny scarcely differs from that of Professor Osborn, 

 save in details. Osborn's characters are as follows : 



Synapsida. - - " A single large supratemporal fenestra ; latero- 

 temporal fenestra rudimentary or wanting. Bony elements of 

 upper and lower arches not separated. Upper arch tending to 

 degenerate first. 



" Squamosals and prosquamosals large, expanded, early coal- 

 esced, forming a portion of the occiput, suturally covering the 

 quadrate, secondarily entering the glenoid fossa. 



1 " Primary Factors of Organic Evolution," p. 115. 



2 "It is uncertain whether this order originated from the Theriodontia or the 

 Rhynchocephalia." In the original it is derived from the Theriodontia. 



