28o 



HISTORICAL PALyEONTOLOGY. 



trunk greatly shortened ; whilst the digits were enclosed in the 

 integuments, and constituted paddles, closely resembling in 

 structure the '•' flippers " of Whales and Dolphins. The neck 

 is sometimes moderately long, but oftener very short, as the 

 great size and weight of the head would have led one to anti- 

 cipate. Bony plates seem in some species to have formed an 

 at any rate partial covering to the skin ; but it is not certain 

 that these integumentary appendages were present in all. Up- 

 on the whole, there can be no doubt but that the Mosasauroid 

 Reptiles — the true " Sea-serpents " of the Cretaceous period — 

 were essentially aquatic in their habits, frequenting the sea, 

 and only occasionally coming to the land. 



The " Mosasauroids " have generally been regarded as a 

 greatly modified group of the Lizards (Lacertilia). Whether 

 this reference be correct or not — and recent investigations 

 render it dubious — the Cretaceous rocks have yielded the 

 remains of small Lizards not widely removed from existing 

 forms. The recent order of the Chelonians is also represented 



in the Cretaceous rocks, 

 by forms closely re- 

 sembling living types. 

 Thus the fresh -water 

 deposits of theWealden 

 have yielded examples 

 of the "Terrapins" or 

 " Mud-Turtles" (i5';;y'j-); 

 and the marine Creta- 

 ceous strata have been 

 found to contain the 

 remains of various spe- 

 cies of Turtles, one of 

 which is here figured 

 (fig. 2 1 1). No true 

 Serpents ( Ophidia)\\2L\Q. 

 as yet been detected in 

 the Cretaceous rocks; 

 and this order does not 

 appear to have come 

 into existence till the 

 Tertiary period. Last- 

 ly, true Crocodiles are 

 known to have existed 

 in considerable num- 

 bers in the Cretaceous period. The oldest of these occur 

 in the fresh-water deposit of the Wealden ; and they differ from 



Fig. 211. — Carapace o^ C lie lone Be7istedi. 

 Lower Chalk. (After Owen.) 



