LONG-NECKED SEA-LIZARDS. 97 



The general dimensions, although perhaps not the 

 absolute length, of these monsters were, however, 

 greatly exceeded by those of a closely allied group 

 of marine reptiles whose remains occur in the Oxford 

 and Kimeridge clays of the great Oolitic series of 

 rocks. These creatures, which are known by the name 

 of Pliosaurs, although agreeing with the Long-Necked 

 Lizards in the structure of their paddles and back- 

 bone, differ very widely from them in having enormous 

 heads, for the support of which a short and thick neck 

 is, of course, absolutely essential. A skull of one of 

 these giants found on the Dorsetshire coast and exhi- 

 bited in the Natural History Museum, is nearly 6 feet 

 in length ; while a hind paddle in the Dorset Museum 

 measures upwards of 6J feet, of which no less than 

 37 inches is taken up by the thigh-bone alone. The 

 enormous biting power and destructive habits of these 

 creatures is evidenced by their teeth, which are not 

 unfrequently found in the Kimeridge clay, and one 

 specimen of which is upwards of a foot in length from 

 the tip of the crown to the base of the root. These 

 teeth are readily distinguished from those of all other 

 reptiles, not only by their huge size, but also by the 

 triangular form assumed by their crowns ; one surface 

 of the triangle being usually nearly smooth, while the 

 other two are ornamented with vertical ridges. 



We may pretty safely assume that in the ancient 

 seas of the Oolitic period the Pliosaurs acted the same 

 part as is played by the ferocious Grampuses in those 

 of the present day. 



