254 



PALEONTOLOGY. 





sides, which are rounded off into each other, and alone shew 

 the longitudinal ridges of the enamel ; these are there very 

 well defined. The vertebrae of the neck are so compressed 

 from before backward as to resemble the vertebrae of the Ich- 

 thyosaurus (fig. 92, c), but the articular surfaces are flat, and 

 as many as twelve may be compressed within the short neck 

 intervening between the skull and scapular arch, as shewn in 



Fig. 94. 

 Pliosaurus (Kimmeridgian). 



fig. 94. For the rest, save in the more massive proportions of 

 the jaws and paddle-bones, the bony framework of Pliosaurtis 

 closely accords with that of Plesiosaurus ; and, as the verte- 

 brae of the trunk resume the plesiosaurian proportions, they 

 give little indication of the genus of reptile to which they truly 

 belong, when found detached and apart. Some individuals 

 of Pliosaurus brachydeirus appear to have attained a length 

 of upwards of 40 feet. A tooth of a Pliosaurus grandis, 

 from the Kimmeridge clay near Oxford, presents the following 

 dimensions : — girth of base of the crown, 7i inches ; diameter 

 of do., 2 in. 7 lines. Both ends of the tooth are broken 

 away, but its length may have exceeded 8 inches ; the general 

 size rivalling that of the teeth of the full-grown cachalot, or 

 sperm-whale.* The remains of this modified form of Sauro- 

 pterygian are peculiar to the Oxfordian and Kimmeridgian 

 divisions of the upper oolitic system ; and, in the counties of 

 England where those clays have been deposited, vertebrae and 



* This specimen is in the collection of the Hon. Kobert Marsham, to whose 

 kindness I am indebted for its inspection. 



