486 



MESOZOIC ERA— AGE OF REPTILES. 



which were twenty to twenty-five feet in alar extent, and another eigh- 

 teen feet. 



The American Pterosaurs differ from all other known Pterosaurs 

 in the fact, recently brought 

 to light by Marsh, that their 

 jaws were entirely toothless, 

 and probably sheathed with 

 horn, as in birds. They have 

 therefore been placed by 

 Marsh in a distinct order, 

 Pteranodontia, from the 

 type genus Pteranodon 

 (winged-toothless). Proba- 

 bly all the American Ptero- 

 saurs belong to this order. 

 One of them, P. ingens, had 



. toothless jaws four feet long, 



1 and an expanse of wing of 



{ twenty-two feet. 



> Among the many Chelo- 



\ nians (turtles) found in the 



I Cretaceous of the Western 



I Plains, of the Rocky Mount- 



f ain region, and of New Jer- 



| sey, one, the Atlantochelys 



I gigcis, had a length of near- 



\ ly thirteen feet, and a 



I breadth across the extended 



g flippers of fifteen feet 



J (Cope). The structure of 



i this huge turtle was singu- 



i larly embryonic. The flat- 



61 tened ribs, which by their 

 coalescence make the greater 

 part of the shell of a turtle, 

 were in this species, as in 

 the embryo of modern tur- 

 tles, not yet cocdesced. 



But the most remarka- 

 ble and characteristic rep- 

 tiles found in the Cretaceous 

 are the Mosasaurs (Pytho- 

 nomorpha of Cope). The 

 first specimen of the order 



