li 



DR. R. BROOM ON THE 



ancestor wliich had a single temporal opening and whose imme- 

 diate descendants lost the posterior squamoso-parietal bar. 



The lizards, though held by most to be derived from a two- 

 arched ancestor like Youngina by the loss of the lower bar, are 

 held by others to be the modified descendants of ancestors which 

 never had more than one temporal opening. 



Some discussion of these debatable points may not be nn- 

 pi'ofitable. 



Text-figure 1. 



A. Skull of Capforliinus acfuti (Cope). 



B. Skull of Pareiasaurns sp. After Watson. 



Cope, Smith Woodward, and all later writers have taken as the 

 primitive reptilian condition of the temporal region a roofed 

 temporal region such as is seen in the Labyrinthodonts or in one 

 of the early Cotylosaurs, such as Pantylus or Lahidosaurns or the 



