PRIMITIVE REPTILES 645 



saurus and the Therapsida; the double vacuities to Ophiacodon 

 and the Rhynchocephalia, et cetera. 



The characters found constantly in all members of either order 

 are given in italics. 



COTYLOSAURIA 



Temporal region unperforate.^ Skull rugose or smooth; rarely 

 with spiny protuberances. Postparietals and quadratojugals al- 

 ivays present. Lacrimals always entering into the posterior border 

 of the nares. Teeth probably always on vomers (prevomers), 

 rarely also on splenials; either thecodont or acrodont. Inter- 

 temporal present or absent, as also either the supratemporal 

 or tabulare, possibly both; primarily with all temporal bones 

 of the StegocephaUa. Quadrate partly uncovered with a supra- 

 tapedial process, or wholly covered. Posterior coracoid some- 

 times unossified. Neck short. Neural arches of presacral verte- 

 brae stout; hyposphenes sometimes present; spines rudimentary 

 or of moderate length; one or two sacral vertebrae; tail moder- 

 ately short or long. Ribs single- or double-headed; abdominal 

 ribs present or absent. Cleithrum well-developed, vestigial, or 

 absent. No puboischiadic vacuity in pelvis. Ungual phalanges 

 often obtuse, sometimes claw-hke. Legs never elongate; ectepi- 

 condylar foramen never present. Rarely with supracostal dermal 

 plates (Diadectes). From twenty-three to twenty-six presacral 

 vertebrae. 



THEROMORPHA 



One or two temporal vacuities on each side. Skull rugose 

 (Casea) or smooth, rarely with spinous protuberances. Post- 

 parietals rarely (Edaphosaurus?) or never present, the tabulare 



8 TheProcolophonia have in no sense a perforated temporal region. I suggested 

 several years ago (Biol. Bull., 1904, p. 166) that the uncovering of the temporal 

 region in Procolophon was due solely to the extension backward of the orbit, and 

 not to the fusion of supratemporal fossa and orbit. This view has been adopted 

 by Huene (Paleontographica, 1912, p. 101) who would, however, give a distinctive 

 term, pseudostegocrotaphic, to the condition found in this genus and its allies. 

 But if this term be used with the Procolophonia, one must consistently use both 

 terms, stegocrotaphic and pseudostegocrotaphic, for the conditions found in 

 the living Chelonia, in Chelone and Chelydra, for instance. 



JOURNAL OF MORPHOLOGY, VOL. 23, NO. 4 



