

REPTILTA. 323 



simply lying upon them. Coracoi'd and pubic bones much ex- 

 panded. Fore and hind extremities with numerous phalangeal 

 bones forming paddles. 



Plesiosaurus CONYB. Head small, neck of great length (20 40 

 vertebrae) ; tail short. Vertebrae either flat or slightly concave. 



Pliosaurus OWEN. Head very large; teeth in distinct sockets 

 with subtrihedral crown. Neck short, with very short vertebrae. 

 Vertebrae in back longer. The articular surfaces of the vertebrae 

 are flat in the cervical, slightly concave in the dorsal, rather more 

 concave in the caudal. 



OWEN states that, as a rule, the length of the vertebrae is constant in 

 Enaliosaurs, in crocodiles and in lizards, whatever other modifications 

 they may undergo. The cervical region both in Pterodactyles and in 

 Pliosaurus forms a remarkable exception; in the first case the vertebrae 

 being much longer, in the other much shorter, than the dorsal vertebrae. 

 Though the teeth are in separate sockets yet the septa are much lower than 

 the outer and inner walls. Report of Br. Assoc. 1841, pp. 6065. 



Ichthyosaurus K(ENIG. Neck short. Head as broad as thorax. 

 Orbits very large; eye with numerous sclerotic plates. Teeth not 

 lodged in distinct sockets, but both the outer and inner plates of 

 alveolar groove are present. Vertebrae deeply biconcave. Tail 

 relatively much longer than in the preceding genus. Probably a 

 caudal crest. 



On the Enaliosaurs see OWEN Rep. of Br. Assoc. for 1839, pp. 43126. 

 Many species of Plesiosaurus and Ichthyosaurus, the former about twice 

 as numerous as the latter, have been found in the secondary strata from 

 the Lias and lower Oolite to the Chalk, when they finally perished in the 

 latter deposit. 



Pterosaur-la OWEN. 



Pterodactylus Cuv., Ornithocephalus SUMMER. Teeth conical, 

 recurved, in separate sockets with wide interspaces. Cervical ver- 

 tebrae longer than the rest. Pectoral extremity modified for flying, 

 the fourth very long, clawless finger appearing to have sustained a 

 membrane. Lithographic limestone (Upper Oolitic system) and 

 the chalk. 



These animals were very various in size: some species from the chalk 

 were gigantic ; the distance between the tips of the wings in Pier. Cuvieri 

 is estimated by OWEN at not less than eighteen feet. OWEN Palceont. Soc. 

 1851, p. 104. 



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