414 ^- W. WILLISTON 



further, and showed their availability, but it was Osborn and 

 McGregor who first applied them definitely. They assumed too 

 much, as we have seen, but the credit is due to Osborn, more than 

 to anyone else, for the foundation of a true reptilian phylogeny, 

 and to him we owe especially a better knowledge of the double- 

 arched reptiles. He has called them the Diapsida, and there is 

 no better name for them. After the elimination of the forms which 

 we are sure do not belong with them, we are all now, I think, in 

 accord as to their phyletic unity. It is only in details that further 

 research (and there is much yet to be done) will be of value. The 

 separation of the great group called the dinosaurs, first proposed 

 by Seeley and warmly espoused of late by von Huene, into two 

 co-ordinate divisions, the Saurischia and Ornithischia, has much 

 to commend it. Valid arguments for the phyletic unity of the 

 pterosaurs, crocodiles, and pseudosuchians have been offered by 

 Huene, and their close relations with the phytosaurs and other 

 "thecodonts" is probable. All of these have certain annectant 

 characters, which, to me at least, are impressive. Altogether they 

 constitute the phyletic group of the Archosauria, a term we owe 

 to Cope. 



The Diaptosauria, the other component group of the Diapsida, 

 is much smaller than when Osborn named it; and of the few forms 

 that are left, one, the Thalattosauria of Merriam, is discordant 

 and uncertain. It has been offered as a connecting link between 

 the true rhynchocephalians and the squamate reptiles; I would 

 rather shift it bodily to the Parapsida. The Diaptosauria are the 

 more generalized diapsids; the distinction between them and 

 the Theromorpha is not great. The earliest assured member of 

 the Diapsida has been carried back, I believe, no farther than late 

 Permian, in Youngina, to which Broom has given the inappropriate 

 group name of Eosuchia, inappropriate because Eosuchus Dollo 

 is a true crocodile. 



The origin of the Diapsida, thanks chiefly to Baur and Case, 

 seems clear. These authors thought that the Pelycosauria were 

 really a part of the Rhynchocephalia, and for years they were 

 classed among them in our textbooks. It was an error, but the 

 error has shown, definitely I think, how the Diapsida arose, by the 



