34 GUIDE TO THE FOSSIL REPTILES, AMPHIBIANS, FISHES 
Cases P, Q. 
Table-case 
26. 
Wall-case 
10 . 
Wall-cases 
11-14. 
fin-membrane extended in a vertical plane (Fig. 29). The 
joints (phalanges) of the toes which form the paddles are 
more numerous than usual, as in the modern whales and 
porpoises. There is no trace of armour. 
The latest Sauropterygia of Cretaceous age seem to have 
been world-wide in distribution, but are illustrated in the 
collection only by fragments. Among these the powerful 
teeth of Polyptychodon (Fig. 30), from the Chalk, Greensand, 
and Gault, are noteworthy (Table-case 26). In the Upper 
Jurassic there are the large-headed short-necked Pliosauria, 
besides the small-headed long-necked Plesiosauria, Plio- 
saurus itself musk have been a gigantic reptile, the skull and 
Fig. 30. — Tooth of Polyptychodon interruptus, from the Cambridge Green¬ 
sand ; one-half nat. size. A portion of the ribbed enamel of the crown 
is shown_on the right, nat. size. (Table-case 26.) 
jaws of P. grandis, from the Kimmeridge Clay, measuring 
6 feet in length, while those of P. ferox , from the Oxford 
Clay, are not much smaller (Wall-case 10). Peloneustes 
(Fig. 31, a), with a slender snout, is an allied animal from the 
Oxford Clay. Cryptoclidus (Plate V.), well represented by 
the two skeletons from the Oxford Clay of Peterborough 
already mentioned (Cases P, Q), does not differ much from 
the Liassic Plesiosaurus (Fig. 29), except in the relations of 
the bones supporting the fore limbs. Plesiosaurus and 
'closely similar genera from the English Lias are represented 
by a unique series of skeletons in Wall-cases 12, 13, 
14. The plaster cast of a partially restored skeleton of 
