22 REVISION OF THE PELYCOSAURIA. 



(5) Only a slight difference in the lengfth of the bottom line of the vertebrse 



in different parts of column. Anterior dorsals without wide face for 

 the intercentrum. 



(6) Character not shown. 



(7) Spines short. 



(8) Spine of axis low and broad. 



(9) Limb bones without well-developed articular faces. 



(10) Character not shown. 



(11) Abdominal scutes present. 



(12) Tail long. 



(13) 600 to 800 mm. long. 



It is evident that Varanosanrus closely resembles Poltosaui-us; the sole 

 diflferences that can be detected in a comparison of the specimen of Polio- 

 saurus with the description of Varanosaurus are the single-headed ribs, 

 the neural arches coossified with the centra, and the elongate head. The 

 first of these characters is most interesting ; in the other members of the 

 Poliosauridce^ which Varanosaurus closely resembles, the ribs are dis- 

 tinctly double-headed throughout the presacral region ; indeed there is not 

 another member of the Pelycosauria in which the ribs are single-headed. 

 The elongate head of Varanosaurus is probably a good character distin- 

 guishing it from PoHosaurus, but the difference was not great ; the head 

 of Poliosaurus was elongate, but probably rather wider and more flattened 

 than Varanosaurus. 



Varanosaurus was almost equally close to the next genus Theropletcra. 

 It dififers in the single-headed ribs and the less well-developed articular 

 condyles on the limb bones of the former. It agrees in the coossification 

 of the neural arches with the centra. The skull of Thcropleura is very 

 fragmentary, but enough remains to show that it was quite elongate ; it 

 seems, however, to have been rather wider and more flattened than that of 

 Varanosaiirus. 



Recent statements made by Broili indicate that the ribs are not truly 

 single-headed, so the distinction between the three genera is not great ; see 

 morphological revision, p. 79. 



Genus THEROPLEURA Cope. 



Chpsydrops Cope. Proc. Am. Phil. Soc, vol. xxii, 1884, p. 30. 

 Diofeiis Cope. Trans. Am. Phil. Soc, vol. xvn, 1892, p. 11. 



Type : An imperfect skull ; complete pelvis ; nearly complete vertebral column ; 

 both femora and tibiae. No. 4155 Am. Mus. Nat. Hist., Cope, coll.; from the valley 

 of the Big Wichita river, Texas. 



Original description : " The quadrate bones of both sides are distinctly displayed. 

 They are rather short, and articulate above by squamosal suture with the squamosal 

 bones, which overlap them posteriorly. They narrow upwards, and are deeply 

 grooved on the anterior face below. Each edge of the groove is produced forwards ; 



