PRIMITIVE REPTILES 647 



quadrat ojugal; they have no cleithrum; ventral ribs are present; 

 and the thoracic ribs are single-headed. 



The Seymouriidae, on the other hand, have all the cranial 

 bones of the Stegocephalia, according to Broili and Williston, 

 namely, the postparietal, intertemporal, supratemporal, tabulare 

 sqamosal and quadratojugal. They have no cleithrum nor 

 ventral ribs; and the thoracic ribs are distinctly double-headed. 



The Pantylidae, known only from the skull, have all the known 

 stegocephalian roof elements of the skull, except the intertemporal; 

 the teeth are acrodont, and are, for the most part, attached to 

 broad palatal and splenial plates. 



The other families of American Cotylosauria all possess a 

 cleithrum, no ventral ribs, and single-headed thoracic ribs. 



While these differences may seem to be important, it is very 

 much of a question whether in such primitive reptiles they mean 

 what they would in later and less plastic types. They do mean, 

 as has been said by Case, that, even as early as the close of the 

 carboniferous times, the most primitive reptiles known to us 

 had already undergone many changes and divergences. 



PROTEROSAURIA 



Paleohatteria. The relationships of Paleohatteria with the 

 American Permocarboniferous Theromorpha are, I believe, in- 

 contestable. Already such relationships have been suggested 

 by Broili and Case, as well as others. Osborn, under the belief 

 that Dimetrodon and the true pelycosaurs possess two temporal 

 vacuities on each side, placed them in his superorder Diapto- 

 sauria; and, for a long while they were classed under the Rhyn- 

 chocephalia in our text-books. 



For many years, ever since its original description indeed, 

 Paleohatteria has been accepted as either directly ancestral to 

 or a member of the Rhynchocephalia. Baur united it with his 

 Proganosauria, which he considered ancestral to all later rep- 

 tiles. Nor can these relationships with the Rhynchocephalia, 

 as first emphasized by Credner, be denied. In my contestation 

 that the Proterosauria are really Theromorpha I am merely 



