LABYRINTHODONTS. 207 



that the results of the comparison might be deemed to be decisive 

 as to the existence of reptiles in the latter formation, which belong 

 to the same natural genus as does one of the most peculiar of the 

 extinct reptiles of the German Keuper. 



So far, therefore, as the geological question, to which reference 

 was made at the beginning of the present section, depends upon the 

 determination of the generic identity of the reptilian fossils in these 

 formations, it must be regarded as supporting the view entertained by 

 Dr. Buckland of the correspondence of the Warwick and Bromsgrove 

 sandstones with the Keuper sandstones of Germany. And if, on the 

 one hand, geology has, in this instance, derived any benefit from 

 microscopical investigations of animal tissues, on the other hand it 

 must be admitted that in no instance has comparative anatomy been 

 more directly indebted to geology than for the fossils, and the 

 stimulus to their microscopic investigation, by means of which a 

 knowledge has been obtained of the most beautiful and complicated 

 modification of dental structure hitherto known, and of which no 

 adequate conception could have been gained from investigations, 

 however close and extensive, of the teeth of existing species of animals. 



88. Labyrinthodon leptognathus. — When the results of this com- 

 parison of the microscopic structure of the tooth of the Lobyrinthodon 

 Jaegeri and of the smaller tooth of the Warwick sandstone were 

 communicated to Dr. Lloyd, he transmitted for my inspection all the 

 fossils from the same stratum which had been deposited in the local 

 or private museums of Warwick and Leamington, with permission to 

 apply the microscopic test to any of the teeth which these fossils 

 might contain. I shall here briefly notice such of these fossils as 

 throw additional Ught on the dental characters of the species to which 

 they belonged. 



The most valuable and characteristic fossil in this respect is the 

 anterior part of one side of the upper jaw, including the nasal 

 bones (PL 63 a, figs. 1 and 3). It shows that the maxillary or facial 

 division of the skull was broad, much depressed and flattened, 

 resembUng in this respect the skull of the gigantic salamander and 

 aUigator, and having the outer surface of the bones strongly sculp- 

 tured by depressions and furrows as in the crocodilian family. 



