REPTILIA. 
35 
Plesiosaurus cramptoni, from the Upper Lias of Whitby Wall-case 
(original in National Museum, Dublin), shows the large 13 - 
size sometimes attained. This specimen (Wall-case 13) 
measures 22 feet in length, and the span to the tip of the 
paddles is 14 feet. 
The Triassic Sauropterygia comprised not only typical Table-cases 
Fig. 31.—Mandibles of Sauropterygia, upper view, without teeth. (A) 
Peloneustes 'philarchus, from the Oxford Clay of Peterborough; one- 
eighth nat. size. (B) Thaumatosaurus indicus, from the Upper 
Jurassic of India; one-seventh nat. size. (C) Plesiosaurus dolicho- 
deirus, from the Lower Lias of Lyme Regis ; one-quarter nat. size. 
aquatic reptiles such as Nothosaurus (Fig. 32) and Pistosaurus 
from the German and Italian Muschelkalk (Table-cases 24 
and 25), but also smaller reptiles with limbs less completely 
adapted for swimming. These are commonly regarded as 
the ancestors of the Plesiosaurs, and as proof that they were 
descended from land animals. Lariosaurus (Fig. 33) and 
