358 GEOLOGY OF THE ISLE OF PURBECK. 



but the crown is strongly marked with numerous 

 sharp, well-defined, longitudinal striae, and there 

 is a prominent ridge down the middle of each side. 

 The successional teeth are often found in the base 

 of the perfect old teeth, as in the crocodile. 

 Some specimens from Tilgate Forest are two 

 inches long, and half an inch in diameter at the 

 base.* The vertebrae are biconcave, and have an 

 irregular medullary cavity in the centre of the 

 bone ; the chevron bones resemble those of the 

 crocodile. 



Fossil Turtles. — Waterworn bones of turtles are 

 very common in the Purbeck strata, and several 

 almost perfect examples of the carapace, or 

 buckler, and of the plastron, or sternal-plates, 

 have been discovered ; a remarkably fine specimen 

 from Purbeck, was exhibited many years since in 

 Mr. Bullock's museum, in Piccadilly. 



Fossil Fishes. — Detached angular scales of the 

 well-known Wealden fish, the Lepidotus, are often 

 met with in the clays and limestones ; and many 

 specimens of the entire fish, of a smaller species 

 of the same genus (Lepidotus minor), have been 

 obtained. The small hemispherical teeth, termed 

 by the quarry-men fishes' eyes, are of very frequent 



" See Fossils of Tilgate Forest, PI. V. figs. 1, 2, 9. 



