LABYRINTHODONTIA 187 



nary characters of size, form, number, and even of presence 

 or absence of teeth, vary much in existing Batrachians ; and 

 the location of teeth on the vomerine bones is the only dental 

 character in winch they differ from all other orders of reptiles. 



The writer's acquaintance with the remarkable fossils 

 under consideration was begun by the examination, in 1840, 

 of portions of teeth from the new red sandstone of Coton End 

 quarry, Warwickshire. The external characters of these teeth 

 corresponded with those (fig. 66) which had previously been 

 discovered by Professor Jaeger in the German Keuper forma- 

 tion in Wirtemberg, and on which the genus Mastodonsavrvs 

 had been founded. 



The results of a microscopic examination of the teeth of the 

 Mastodonsaurus from the German Keuper, and of those from 

 the new red sandstone of Warwickshire, proved that the teeth 

 from both localities possessed in common a very remarkable 

 and complicated structure (fig. 67), to the principle of which, 

 — viz., the convergence of numerous inflected folds of the 

 external layer of cement towards the pulp-cavity, — a very 

 slight approach was made in the fang of the tooth of the 

 Ichthyosaurus, whilst a closer approximation to the labyrinthic 

 structure hi question was made by the teeth of several species 

 of ganoid fishes, and by those of Archegosaurus. 



Thus, inasmuch as the extinct animals in question mani- 

 fested in the intimate structure of their teeth an affinity to 

 fishes, it might be expected that, if they actually belonged to 

 the class of reptiles, the rest of their structure would manifest 

 the characters of the lowest order, — viz., the Batrachia, the 

 existing members of which pass, though not by the dental cha- 

 racter alluded to, yet by so many other remarkable degrada- 

 tions of structure, towards fishes. 



In the same formation in Wirtemberg from which the laby- 

 rinthic teeth of the so-called Mastodonsaurus had been derived, a 

 fragment of the posterior portion of the skull lias been obtained, 



