THE COTYLOSAURIA 147 



ally be placed there, and in the genus Labidosaurus until such time 

 as Cope's types have been examined and compared. The specitic or 

 even generic identity, however, matters little at present. The more 

 important matter is, what relation does the form have to Procolophon 

 and Telerpeton especially. 



Boulenger has shown, forcefully I think, the relationship between 

 Procolophon and Telerpeton,^ about the only differences which he 

 found being the absence of ventral ribs in Telerpeton. Seeley^ and 

 Broom^ have, more recently, added to this the newly discovered 

 characters of the acrodont and transverse teeth, ^ and it is on the 

 strength of these differences, in face of the resemblances, that Broom 

 would associate Procoloplwn with the Rhynchocephalia, et al., in the 

 superorder Diaptosauria and in the phylum Diapsida, arguing that, 

 in any phylogenic classification the separation of the phyla should be 

 carried back to the very beginning, even though the earliest forms may 

 differ vastly more from the later ones than they do from those immedi- 

 ately preceding them. It is true that, so far, no reptile with a roofed 

 over skull, save Procolophon (and of course the Chelonia) has been 

 found to possess abdominal ribs, so commonly present among the 

 saurocrotaphous reptiles. Indeed, of the single-arched reptiles only 

 the Sauropterygia and Ichthyosauria have such ribs, and, carrying 

 the argument to its extreme, Broom would unite both of these with 

 the subclass Diapsida of Osborn, quite vitiating the original meaning 

 of the term and requiring a new name for the modified phylum. But 

 it is a more difficult thing to treat the Chelonia in the same way. No 

 one has yet had the temerity to transfer the Chelonia to the Diapsida 

 and we are forced to the inevitable conclusion that both of these 

 reputed subclasses, the Diapsida and Synapsida, had abdominal 

 ribs. And indeed such a conclusion is beyond dispute; certainly 

 the oldest reptiles must have had ventral ribs and they must have 

 been essentially Cotylosaurian in structure, for these reptiles, espe- 



I Proceedings of the Zoological Society, London, 1904, p. 476. 



' Ibid., London, 1905. 



3lbid., 1905. 



4 It is of interest to observe that the genera Phanerosaurus and Stephano spondylus 

 according to Stappenbeck, have acrodont teeth placed transversely, and surely they 

 are not also related to the Rhynchocephalia {Zeitschrift d. deutsch. Geolog. Gesell- 

 schaft, 1905, p. 379). 



