LABYRINTHODONTS. 199 



Of such reptiles the least ambiguous and most characteristic remains 

 were the occipital bone of the Salamandro'ides giganteus of Prof. 

 Jaeger : and the teeth of the so called Mastodonsaurus and Phy- 

 tosaurus. On the other hand, the reptilian remains of the War- 

 wick sandstone were still more meagre : no portion of the skull 

 whereby their batrachian character could be tested was then known ; 

 the vertebra, as figured in the Memoir cited, apparently presented the 

 characters of those of the Saurian re ptiles(l) ; and the teeth, therefore, 

 appeared to be the only fossils on which any comparison likely to solve 

 the question of the relationship between the reptiles of the German 

 Keuper and of the Warwick sandstone could be founded. 



Now it has been seen that the teeth of the Mastodonsaurus are of 

 a simple and common form ; that they are far from possessing those 

 well-marked external characters whereby the anatomist can dis- 

 tinguish the teeth of the Iguanodon, Megalosaurus or Pleiosaurus. 



Of the teeth which had been discovered in the Warwick sandstone, 

 the specimen figured in Messrs. Murchison and Strickland's Memoir, 

 and which was transmitted to me for examination together with 

 a similar but larger tooth, most nearly resembled the teeth of the 

 Mastodonsaurus, in its conical figure and longitudinal striation ; but 

 as these were the commonest characters of Saurian teeth no weight 

 could be attached to them as proving a specific or generic identity, 

 bearing upon a geological problem of so much nicety as the one 

 which related to the Warwick sandstones. 



There only remained, therefore, to resort to the test of the inti- 

 mate structure of the teeth in question, and upon application to Prof. 

 Jaeger of Stuttgard, I was favoured with some portions of the teeth 

 of the Mastodonsaurus Jaegeri from which were prepared trans- 

 verse and longitudinal sections for microscopical examination. 



Hitherto in investigating the intimate texture of the teeth of the 

 Saurian reptiles, as the Crocodile, Plesiosaur, Megalosaur, Monitor, 

 and most recent Lacertians, I had found the dentine or body of the 

 tooth to consist of the finest calcigerous tubes, radiating according to 

 the usual law, from the pulp-cavity, at right angles to the external sur- 

 face of the tooth, which is covered by a simple investment of enamel ; 



(1) Subsequent examination has pi'ovecl this vertebra to have a concave articular surface 

 at both ends of the body, and to agree in other characters with the Salamandroid type. 



