HEPTILIA 



285 



The diagram 

 (fig. 83) gives a 

 concise view of 

 the geological re- 

 lations, or distri- 

 bution in time, 

 of the principal 

 groups of the class 

 Reptilia. In the 

 column opposite 

 the right hand, the 

 dark mark shows 

 that the ganoce- 

 phalous group re- 

 presented by the 

 Archcgosaurus be- 

 gan, culminated, 

 and ended in 

 the carboniferous 

 period. The Laby- 

 rinthodonts, cul- 

 minating in the 

 ferias, disappear at 

 the base of the 

 ddli tic system. Of 

 the true Batra- 

 chia, those retain- 

 ing the tail appeal' 

 to have been at 

 their maximum 

 during the upper 

 tertiary period, 

 and to have begun 

 to decline after 



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