PALiEOSAURUS. 267 



rather slender, compressed and acutely pointed, with an anterior and 

 posterior finely serrated edge, the serratures being directed towards the 

 apex of the tooth ; the outer surface is more convex than the inner 

 one : the apex is slightly recurved : the base of the crown contracts a 

 little to form the fang, which is subcylindrical. The pulp-cavity 

 remains open in the base of the crown. 



In microscopic structure, the teeth of the Palseosaurus closely 

 correspond with that of the teeth of the Varanus, Monitor and Mega- 

 losaurus. The body of the tooth consists of compact dentine, in 

 which the calcigerous tubes diverge from the 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 30^0^1^ of an inch : the breadth of the interspaces is -ith of an inch. 

 The crown of the tooth is invested with a simple coat of enamel. 



This examination, which I have been enabled to make by the kind- 

 ness 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, already 

 described under the name of Labyrinthodon. 



1 l^.Palceosaurus.—ln the same formation as contained the jaw and 

 teeth of the Thecodontosaurus, two other teeth were separately dis- 

 covered, differing from the preceding and from each other ; the crown 

 of one of these teeth, measuring nine lines in length and five lines in 

 breadth, is represented at PL 62 a, fig. 7. It is compressed, pointed, 

 with opposite trenchant and serrated margins, but its breadth, as 

 compared with its length, is so much greater than in the Thecodon- 

 tosaurus, that Dr. Riley and Mr. Stutchbury have founded upon it 

 the genus Palaosaurus,{\) and distinguish it by the specific name 

 of platyodon, from the second tooth which they refer to the same 

 genus under the name of Palcsosaurus cylindrodon. The portion of the 

 tooth of the Pal. cylindrodon which has been preserved, shows that the 

 crown is sub -compressed and traversed by two opposite finely-serrated 

 ridges, its length is five lines ; its breadth at the base two lines. 



(1) Loc. cit. p. 352. 



