72 Mr. D. M. S. Watson on the 



Preparietal. — Tliis bone is exactly similar to that of- 

 Anoniodonts ; its homologies remain obscure, but it is quite 

 certain that it does not represent a fused pair of parietals. 

 This is the first recorded occurrence of the bone out of the 

 order Anomodontia. 



General Discussion of the Palate. 



The specimen which is the subject of this paper agrees so 

 closely with Gorgonops that we are justified in combining the 

 well-known preorbital part of the skull of that genus with it 

 to get a complete knowledge of the palate. 



The palate of Gorgonops^ is on the whole very similar to 

 that of Scylacosaurus as described by Broom. There are the 

 same large prevomers separating very large posterior nares. 



Gorgonops siiows, however, in an exaggerated form a 

 feature which is present in many diverse early Therocephalian 

 genera; that the tooth-bearing edge of the premaxilla lies 

 considerably above that of the maxilla, so that there is a step 

 in the outline of the jaw. Tliis curious feature also occurs in 

 Dimetrodon, so that it is possible that it is a primitive feature. 

 I tiiink on the whole, however, that it has been indepen- 

 dently acquired, owing to latent homoplasty, on several 

 different lines of descent. 



It is of great importance, because it results in the pre- 

 vomers, which are directly attached to the palatal {)rocesses 

 of the premaxillse, being raised considerably above the level 

 of the tooth-bearing edge of the maxilla?. This is the explana- 

 tion of the fact that in mammals the palatine processes of 

 the premaxillai articulate with the anterior end of the vomer 

 in such types as the dogs. Like the vomer they belong to 

 the original primitive palate and lie above the level of the 

 secondary plates of the maxillte and palatines. In Gorgonops 

 the lower borders of the maxillge are somewhat approxi- 

 mated, so as to tend towards the formation of a secondary 

 palatal plate. This early stage in the formation of a 

 secondary palate by the raising of the prevomers above the 

 level of the lower edge of the maxilla? and the incipient 

 production of secondary palatal plates from the latter bones 

 is exactly paralleled by Belodon, which sliows a morpholo- 

 gical stage in the evolution of the Crocodilian secondary 

 palate. 



Another large much- weathered Therocephalian skull * in 



* BeloDging to a different family. 



