238 PERMIAN FOSSILS. 



Genus TJiecodontosaurus, Riley and Stutchbury. 



"The genus Thecodontosaurus \s founded on the structure of the teeth, and their 

 having been deposited in distinct alveoh."^ In these characters it is alhed to the 

 typical Varanian Monitors ; but with this difference, that the teeth are " imbedded in 

 distinct sockets ; to this condition, however, the Varani, among the squamate Saurians» 

 make an approach in the shallow cavities containing the base of the teeth along the 

 bottom of the alveolar groove. 



" In the ancient extinct genus in question the sockets are deeper, and the inner 

 alveolar wall is nearly as high as the outer one ; the teeth are arranged in a close-set 

 series, slightly decreasing in size towards the posterior part of the jaw ; each ramus of 

 the lower jaw is supposed to have contained twenty-one teeth. These are conical, 

 rather slender, compressed and acutely pointed, with an anterior and posterior finely- 

 serrated edge, the serratures being directed towards the apex of the tooth, as in the 

 genus Bho^alodon of G. Fischer ; the outer surface is more convex than in the inner 

 one ; the apex is slightly recurved ; the base of the crown contracts a little to form 

 the fang, which is sub-cylindrical. The pulp-cavity remains open in the base of the 

 crown. In their microscopic structure, the teeth of Thecodontosaurus closely correspond 

 with that of the teeth of the Varanus, Monitor, and Megalosaurus. The body of the 

 tooth consists of compact dentine, in which the calcigerous tubes diverge from 

 an open pulp-cavity at nearly right angles to the surface of the tooth ; they form a 

 slight curve at their origin, with the concavity directed towards the base of the tooth ; 

 then proceed straight, and at the periphery bend upwards in the contrary direction. 

 The diameter of the calcigerous tube is T^,Vo"o-tb of an inch ; the breadth of the 

 interspace of the tubes is ^oVo of ^^ inch. The crown of the tooth is invested with a 

 simple coat of enamel."' 



" The microscopic examination of the structure of the teeth, which I have been 

 enabled to make by the kindness of Mr. Stutchbury, satisfactorily establishes the 

 distinction between the Saurian of the Bristol conglomerate, and the reptiles of the 

 later member of the new red sandstone system in Warwickshire, which I have 

 described under the name of Lahyrinthodonr (Owen, Op. cit.) 



Thecodontosaurus antiquus, Biley and Stutchbury. 



Saurian, Williams. Proceedings of the Geol. Soc. Lend., vol. ii, p. 112, 1834. 

 Thecodontosaurus, Riley and Shitchbury. Proceedings of the Geol. Soc. Lend,, 



vol. ii, p. 398, 1836. 



^ Riley and Stutchbury Proceedings of the Geol. Soc, vol. ii, p. 398. 



