848 HISTORICAL GEOLOGY. 



almost solely to a skull found in the uppermost Cretaceous beds of Belgium, 

 on the river Meuse, 1785, whence was derived the name Mosasaurus. The 

 first American species was a tooth in a fragment of a jaw, found at Mon- 

 mouth, ]Sr. J., and figured in S. L. Mitchill's Geology of North America, 

 1818, described by Dekay in 1830, and named Mosasaurus major by him in 

 1841. Previously it had been named M. Dekay i by Bronn (1838). The 

 tooth, according to Dekay, was 1-06 inches long and 1-02 and 1-33 broad 

 at base. Through the discoveries since made, the number of American 

 species described is near 50 ; and their remains have come from the borders 

 of the Atlantic and the Mexican Gulf, and from the Interior Continental 

 seas in Kansas, Dakota, Colorado, and beyond. Kansas is credited with 25 

 or more Mosasaurids from the Niobrara beds. 



The species are related, like true Snakes, to the Lacertians ; but they had 

 paddles, and a skulling tail which was nearly half the length of the body, as 

 shown in the restoration of Edestosaurus ( Cliclastes) velox of Marsh, by S. W. 

 Williston, in the following figure. The Clidastes iguanavus of Cope is from 



1417. 



Eestoration of Edestosaurus (Clidastes) velox (x 7*5). Williston. 



the Lower Greensand, New Jersey, and C. propytlion of Cope, from the 

 Rotten Limestone in Alabama. Baptosaurus platys2yondylus and B. fraternus, 

 both of Marsh, are from the Upper Greensand of New Jersey. 



One of the fore paddles of Lestosaurus of Marsh is represented, much 

 reduced, in Fig. 1420. Fig. 1418 represents the tooth of Mosasaurus princeps 

 of Marsh, from New Jersey, and 1419, the head extremity of one of the 

 Mosasaurids, showing the bases of four teeth. An anomaly in Mosasaurus is 

 the existence of an articulation for lateral motion in either ramus of the 

 lower jaw (at a in Fig. 1421), where there is in all other Reptiles a suture 

 only ; a fact first recognized by Cope. Besides, the extremities of the two 

 rami were free, so that they could serve like a pair of arms in the process of 

 swallowing whole a large animal. 



True >S'?iaA;es are rare species in the Mesozoic. The Coniophis precedens 

 of Marsh, the only one known in this country, occurs in the same beds with 

 the remains of the Ceratopsidae in eastern Wyoming. 



Crocodilians were represented by the Thoracosaurus of Leidy (the J^ew 

 Jersey Gavial, or Gavialis Neocesariensis of De Kay, 1833), Holops pneu- 

 maticus and Gavialis fraterculus, of Cope, from New Jersey, and other species 

 having the vertebrae concavo-convex, as in true _Crocodiles. The older type, 

 with biconcave vertebrae, also was represented; and Hyposaurus Rogersi 

 Owen (1849) from New Jersey, and H. Webbii Cope from Kansas are exam- 



