CETIOSAURTJS. 325 



animals are supposed to have been of aquatic, and 

 probably of marine, habits, on the evidence of the 

 sub-biconcave structure of the vertebra?, and of the 

 coarse cancellous tissue of the long bones, which 

 are destitute of a medullary cavity. They must 

 have rivalled the whales in bulk, for some remains 

 indicate a length of forty or fifty feet.* 



Streptospondylus. — Among the large verte- 

 brae washed up on the shore in Brixton Bay, I 

 found several with one end convex and the other 

 concave ; these belong to the extinct crocodilian 

 reptile called Streptospondylus (meaning reversed- 

 spine), because these vertebrae are arranged in the 

 spinal column in a position the reverse of that 

 which obtains in all other reptiles of the same 

 osteological type ; for the convexity or ball of the 

 vertebrae is placed anteriorly, whereas in the cro- 

 codile, &c. it is in the opposite direction. f The 

 original, in its form and habits, probably bore a 

 general relation to the crocodiles. 



Plesiosaurus. — The splendid collection in the 

 British Museum, which contains several perfect 

 skeletons of different species of this genus of ex- 

 tinct marine reptiles, must be too well known to 

 render any description necessary of the osteological 



* Medals of Creation, vol. ii. p. /26. 



t Cuvier's Reckercltes stir les Ossemens Fossiles. Tom. V. pi. 6. 



