54 



THE HISTORY OF THE PELYCOSAURIA, WTTH 



of the skull, formed by a nearly vertical plate, concave from side to side, formed from 

 the union of the exoceipitals, the supraoccipital, the basioccipital and the paroccipitals, 

 the whole bearing a strong resemblance to the same region in Dicynodon. The upper 

 and lower temporal arches both present ; very short in the anteroposterior direction. The 

 parietal and the superior arch descend rapidly to join the posterior end of the lower arch. 

 The superior temporal vacuity much smaller than the lower. The quadrate greatly 

 depressed and nearly enclosed by the surrounding hones. The lower face of the quad- 

 rate marked by two deep parallel grooves which received two corresponding processes 

 on the articular hone of the lower jaw, thus limiting the motion of the lower jaw to the 

 vertical plane. The nares open directly into the mouth at the anterior extremity. The 

 pterygoids, palatines and vomers are covered by many small teeth. The ribs are two- 

 headed in the dorsal region, the capitulum attaching to the intercentrum preceding. The 

 neural spines of the vertebrae elevated or not. Limbs very short and strong. The humerus 

 with an entepicondylar foramen and a notch representing the eetepicondylar foramen. 

 The hind foot possessing both calcaneum and astragalus. A free; eentrale in the tarsus. 



Under the Pelycosauria, as here defined, it seems possible to place with a, consider- 

 able degree of certainty forms from all the regions which have furnished Permian verte- 

 brate fossils. The following are the genera comprising the group as well as can be made 

 out at present : 



American forms : 



Clepsydrops. 



Dimetrodon. 



Embolophorout. 



Theropkura (doubtfully distinct). 



Melar-mosaurus (doubtfully distinct). 

 Archaobolv,! (doubtfully distinct). 

 LysorophuB. 

 Naotaurui. 



Bohemian forms 



Naosaurua. 



French forms 

 OallibracMon. 



(?) 



b'tereoracJiis. 



Russian forms : 



Deuterosaurus. 

 RhopJialodon. 



C'liorhizodon (?). 



South African forms : 



, Wlurotaurus. 

 Lycosaurus. 



Oynodraco. 

 OynosucJius (?). 



