DRAGONS OF THE DEEP. 199 



jaws well armed with teeth, and fed, as we 

 know from the remains of prey found in the 

 bodies of the fossils, on the mail-clad fishes which 

 abounded in the seas of that time, and on the 

 young of their own kind, many of the later 

 members of this tribe were entirely toothless. 

 These toothless forms occur in the Upper Jurassic 

 rocks. They probably lived on cuttle-fish and 

 similar boneless creatures. Furthermore, we 

 may trace other phases in the evolution and 



FIG. 17. Outline restoration of an extinct Fish-lizard (Ichthyosaurus). 

 Note the downwardly directed tail seen through the lower lobe of 

 the tail fin. After Fraas. 



decline of the teeth. In the members of the 

 Triassic age the teeth were irregular in size ; 

 during the Liassic times they became uniform in 

 size ; and finally in the Jurassic and Cretaceous 

 we find almost a quite toothless species. But 

 to this question of the teeth we must return 

 later. 



The general form of the body of these crea- 

 tures, as will be seen in Fig. 16, was remarkably 

 whale-like, but a little scrutiny will quickly 

 reveal many points wherein they are peculiar. 

 In the first place, the back was provided with 

 several fin-like structures, which served as 



