THE GREAT SEA-LIZARDS AND THEIR ALLIES. 55 



to ten feet in length. But in the rocks of the Cretaceous period, 

 which was later, are found larger specimens. There is a cast of a 

 very fine specimen from the Upper Lias on the wall of the east 

 corridor (No. 3 on Plan) of the geological galleries at South 



FiG. 7. Mandibles of Fish-lizards. A, Peloneustes philarchus (Seeley) ; 

 from the Oxford Clay. B, Thaumatosaurus indicus (Lydekker) ; Upper 

 Jurassic of India. c, Plesiosaurus dolichodirus (Conybeare) ; from the 

 Lower Lias, Lyme Regis. 



Kensington, which is twenty-two feet long. But some of the 

 Cretaceous forms, both in Europe and America, attained a length 

 of forty feet, and had vertebrae six inches in diameter. The 

 bodies of the vertebrae, or " cup-bones," are either flat or slightly 



