AGES OF NATTJBE. 405 



sidered as the prototypes of the whales, having, like them, 

 limbs in the form of oars. The Plesiosaurus (fig. 383) agrees, 

 in many respects, with the Ichthyosaurus in its structure, 

 but is easily distinguished by its long neck, which somewhat 

 resembles the neck of some aquatic birds. A still more ex- 

 traordinary reptile is the Pterodactylus (fig. 384), with its 

 long fingers, like those of a bat, for the support of wings, by 

 which it was enabled to fly. 



Fig. 384 . Pterodactylu8jerassirostris.--G()\3fass t 



6/4. It is also in the upper stages of this formation that 

 we meet with the skeletons of tortoises. Here also we find 

 the remains of several families of insects (Lifiellulce, Coleop- 

 tera, Ichneumons, $-c.) Finally, in these same stages, the slates 

 of Stonesfield, the first traces of mammals are found, namely, 

 the jaws and teeth of animals belonging to extinct forms of 



