of Wirtemherg and Warwickshire. 505 



wise, between the Warwick sandstone reptiles and those of the German Keuper, can 

 be founded. 



It happens, however, that the teeth of the so-called Mastodonsaurus or Salaman- 

 dro'ides are of a very common and simple form ; they are far from possessing those 

 well-marked external characters that enable the anatomist to distinguish at a glance 

 the teeth of the Iguanodon or Megalosaurus. 



Of the teeth which have been discovered in the Warwick sandstone, the specimen 

 figured in the memoir of Messrs. Murchison and Strickland (Trans. Geol. Soc. vol. v. 

 PI. XXVIII. fig. 8.), and which has been transmitted to me for examination, 

 together with other fossil teeth, by Dr. Lloyd of Leamington, most nearly resembles 

 the teeth of the Mastodonsaurus, in its conical figure and longitudinal striation ; 

 but as these are the commonest characters of reptilian teeth, no weight could be 

 attached to them as proving a specific or generic identity, bearing upon a geological 

 problem of so much difficulty as the one which attaches itself to the Warwickshire 

 sandstones. 



There only remained, therefore, to resort to the test of the intimate structure 

 of the teeth in question ; and by the kindness of Professors Jaeger and Plieninger 

 of Stuttgard, I have been favoured with some portions of the teeth of the Masto- 

 donsaurus Jageri, from which have been prepared the requisite sections for mi- 

 croscopical examination. 



A close similarity prevails in the intimate texture of the teeth of the Crocodile, 

 Plesiosaur, Megalosaur, Monitor, and most recent Lacertians, in which the dentine, 

 or body of the tooth, consists entirely of the finest calcigerous tubes, radiating, 

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

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

 from the prevalence in the Saurian order of this, the ordinary structure of simple 

 conical teeth, I did not build any very strong hopes of detecting such modifications 

 of dental structure in the similarly shaped teeth of the so-called Mastodonsaurus, 

 and of the reptile from the Warwick sandstone, as would be sufficiently marked 

 and obvious to convince those who might not be familiar with the value of such 

 characters, of their specific or even generic identity; but from this fear I have been 

 agreeably and unexpectedly relieved. 



The first transparent transverse section of the tooth of the Mastodonsaurus 

 Jcsgeri which was placed under the microscope, and viewed by transmitted light 

 with a low magnifying power, presented the singularly complicated structure ex- 

 hibited in the subjoined woodcut ; which structure, the anatomist conversant with 

 the known modifications of dental structure in the animal kingdom, may well con- 

 ceive not to have been contemplated without much surprise. 



It was not, indeed, until I had caused sections of the portions of the tooth of this 



