236 



WATER REPTILES OF THE PAST AND PRESENT 



front legs were strong flippers, the humerus was long and stout, 

 with the crest for the attachment of muscles far down on the 

 shaft; the digits were greatly elongated and clawless, etc. The 

 plastron only was less reduced than in the case of the modern sea- 

 turtles. No traces of horny shields have been discovered. As to 

 the nature of the covering and the general appearance of the 



Fig. 125. — Archelon; skeleton from below: Av, hyoplastron ; A/»/>, hypoplastron. 

 (From Wieland.) 



turtle when alive, Dr. Wieland has kindly given the writer his 

 views, as follows: 



''After direct study or fairly close examination of all the fossil 

 material of importance thus far collected representing the Pro- 

 tostegidae, it seems certain that in all the members of the group 

 an external leathery layer was well developed. In no instance is 

 there the slightest trace of horny shield sulci, or grooves; though 

 it seems probable that there was some gradation toward a thin and 

 perhaps even slightly horny hide. In Archelon ischyros the re- 

 duced condition of the carapace and the presence of the continuous 



