346 Structure of the Fossil Saurians. 



and of most of the Mammalia. The limbs were longer, and 

 were provided with more pointed paddles, and were certainly 

 more flexible than those of the Ichthyosaurus. The tail, 

 from its shortness, does not remind us of a Saurian. The 

 thin and long neck resembles the body of a snake. The 

 structure of this animal is one of the most peculiar in the 

 whole creation. It is probable, that, on more extensive in- 

 vestigation, one or more species of the Plesiosaurus will be 

 established, in addition to those now described. 



a. Plesiosau'rus dolichodei n rus Conybeare. 

 To this species belong the more complete skeletons which 

 are chiefly found in England, and from which the character- 

 istics of the genus were derived. 



b. Plesiosau'rus rece'ntior Conybeare. 

 The vertebrae which gave occasion to this species are, 

 throughout, shorter than those of the P. dolichodeirus, and as 

 flat as the vertebrae of the Ichthyosaurus; their surfaces, 

 however, are not so concave : on the lower side of the ver- 

 tebrae the small holes already mentioned are seen. These 

 vertebrae were found in the Kimmeridge clay. 



c. Plesiosau'rus carina x tus Cuvier. 

 A cervical vertebra, found, probably, in the oolite of Bou- 

 logne, is distinguished on its lower side, between the two holes, 

 by a blunt longitudinal edge, and has given occasion to this 

 species. 



d. Plesiosau'rus pentago v nus Cuvier. 



Cuvier possessed caudal vertebrae from Auxois, the body 

 of which, instead of being cylindrical, was completely penta- 

 gonal, from which he named this species. 



e. Plesiosau'rus trigo^nus Cuvier. 

 A vertebra, from the coast of Calvador, is triangular, like 

 some of those of the Mososaurus, that is, it is flat and broad 

 below, and decreases above. On the sides of the lower sur- 

 face lie its transverse processes. 



/. Plesiosau'rus macroce'phalus Conybeare. 



Of this species, which was discovered by De la Beche in 

 the lias of Lyme Regis, no description is known to me. 



g. Plesiosau'rus Cuvier, 

 Puillon-Boblaye discovered, in the lower part of the blue 

 marls of Stenay, which lie between the Oxford clay and the 

 cornbrash, a considerable portion of the skeleton of a Plesio- 

 saurus, which Cuvier conceives to belong to a new species. 



