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, Peloneiistes philarchus (Seeley) ; 
from the Oxford Clay. B, Thaumaiosaurus indicics (Lydekker) ; Upper 
Jurassic of India. c, Plesiosaicrus dolichodirns (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 
