from the Portland Limestone. 



183 



Cervical vertebra. — The centrum measures 2 inclies from 

 back to front at its base, and is slightly longer under the 

 neural arch. The articular surface of the centrum is elliptical, 

 2'i inches broad, and nearly 2 inches high. It is very slightly 

 and regularly concave, so as to 

 appear nearly flat ; and in the 

 centre there is a small sudden 

 depression, as in Pliosavrvs 

 hrachyspondyJus (Owen). The 

 margin under the neural canal 

 is concave ; and the remainder 

 of the margin of the articular 

 surface of the centrum is ob- 

 liquely bevelled, as is often 

 seen in cervical vertebras of 

 Plesiosaurs. The base of the 

 centrum is concave from back 

 to front, in which direction 

 there is a moderate ridge me- 

 sially, with the usual nutritive 

 foramen on each side of it ; the 

 interspace between these fora- 

 mina is a quarter of an inch. 

 The base of the centrum is 

 separated from the side by the 

 articulation for the cervical rib. 

 This articulation is transversely 

 elliptical, f of an inch high, and 

 more than an inch long ; it is deeply concave from front to 

 back, and nearer to the posterior than to the anterior articular 

 surface of the centrum, as is usual. On the left side of the 

 centrum the cervical rib is preserved ; it is about f of an inch 

 long, much compressed from side to side, directed downward 

 and outward and backward, and tapering from back to front. 

 The side of the centrum is smooth, gently concave between 

 the back and front, where it terminates in the thickened 

 margins of the articular surfaces ; it is convex from below 

 upward. 



The suture between tlie neural arch and the centrum re- 

 mains persistent ; but the two neurapophyses are anchylosed 

 into one mass, and do not remain distinct as in Pliosaurus. 

 The whole neural arch is directed obliquely backward, much 

 compressed from side to side ; the neural spine is long, as 

 in Plesiosaurus ; and the arch does not articulate with the 

 centrum by ovate pedicles as in Pliosaurus ; so that both in 



Side view of the same cervical 

 vertebra of P. icinspitensis, one- 

 half natural size. 



