404 



GEOLOGICAL SUCCESSION OF AJSTIMALS. 



therium, from the resemblance of the impressions to a hand. 

 The mollusca, articulate, and radiata approach those of the 



fauna of the suc- 

 ceeding period. 



673. The 

 Oolitic fauna is 

 remarkable for 

 the great number 

 of gigantic rep- 

 tiles it contains. 

 In this formation 

 we find those 

 enormous amphi- 

 bia, known under 

 the name Ichthy- 

 osaurus, Plesio- 

 saurus, and Me- 

 galosaurus. The 

 first, in particular, 

 the Ichthyosauri, 

 greatly abounded 

 on the coasts of 

 the continents of 

 that period, and 

 their skeletons are 

 so well preserved, 

 that we are ena- 

 bled to study even 

 the minutest de- 

 tails of their struc- 

 ture, which differs 

 essentially from 

 that of the rep- 

 tiles of the pre- 

 sent day. In 

 some respects 

 they form an in- 

 termediate link 

 between fishes 

 and mammals, 

 Fig. 383. Plesiosaurus rvgosus.Ovren. and may be con- 



