FIG. 18. A. Left- arm of Crocodile, showing the normal form of the 

 walking limb in Reptiles. B. The arm of an extinct ally of the 

 long-necked Lizards (Plesiosaurs), showing the conversion of the 

 limb into a paddle. C. The arm of the Plesiosaur, showing 

 further evolution of the paddle. D. The arm of the extinct 

 Crocodile Geosaurus, showing its transformation into a paddle. 

 E. The arm of the Hawksbill Turtle, showing the same modifica- 

 tion. F. The paddle of the old Fish-lizard Ichthyosaurus, showing 

 the most extreme point reached in the evolution of the paddle. 



A=Humerus or arm bone. F= Fore-arm. w= Wrist-bones. 

 D= Digits. 



