VERTEBEATA 65 



The order Theromora includes five saborders, and per- 

 haps others. They differ as follows : 



I. Palate imperforate ; interior nares posterior. 

 Teeth molariform ; one occipital condyle ; Placodonta. 



II. Palate perforated anteriorly for internal nares. 



a, Occipital condyle single. 

 Dentition complete, teeth compressed ; Thcriodonta. 



Teeth absent or reduced to one pair above ; Anoinodonfa. 



aa, Occipital condyles two. 

 Teeth compressed ; Ci/nodonta. 



Teeth molariform ; Gomphodonta. 



Some of the suborders are imperfectly known. In all of 

 them it is probable, and in many of them certain, that the 

 supratemporal bone extends forward above the malar nearly 

 to the orbit, and that it sometimes includes, with the latter, 

 a foramen (Cynodonta), thus simulating two postorbital 

 bars. In the Gomphodonta and Cynodonta the two occipi- 

 tal condyles correspond with those of Mammals, and the 

 quadrate is so abbreviated as to render it highly probable 

 that these groups are the ancestors of the Mammalia. With 

 the extreme shortening of the quadrate the quadrato-jugal 

 bone disappears, and the supratemporal becomes the zygo- 

 matic part of the squamosal of the Mammal. In these 

 suborders and in many of theTheriodonta, the canine teeth 

 are greatly enlarged. The families are as follows : 

 Placodonta : Placodontidse, Trias of Europe. 

 Theriodonta: PProterosauridee, Permian of Europe; Rhyn- 



chosauridse, Trias of Europe and India ; Lycosauridas, 



Permo-Trias of South Africa and Europe. 

 Axomodonta; Dicynodontidse (Fig. 20), Permo-Trias of 



South Africa, Asia and Europe. 

 Cynodonta : Galesauridse, Permo-Trias of South Africa. 

 Gomphodonta : Tritylodontidse, Permo-Trias of South 



Africa. 



