372 THE PORTLAND OOLITE PERIOD. CHAP. 



v^^ \^^ 1t 



n " 



Diagram CLXXII. Caudal vertebra of Plesiosaurus validus. 

 i. In front. 2. On the left side. 3. Below. 4. Above. 



The length of the largest (say 5th caudal) is 2*3 inches ; of the 

 smallest known (say 23rd), 1-5. The height of the largest is 3*25 

 inches; of the smallest (23rd), 1-9. 



Counting from the largest to the smallest, we have i + interval 

 6, -f i -f interval 10, + i, = 19, and beyond this interval 1 1, making 

 in all 30. To this we must add say 4, for anterior caudals not re- 

 covered ; the total equals 34, a probable number. 



These caudal vertebrae are much alike through the whole series ; 

 all having biconcave faces, neatly bordered ; broad striated neural 

 canal ; prominent lateral processes, and very large and conspicuous 

 separate haemal cicatrices on the posterior edge. Parts of the neural 

 and lateral processes are sometimes found attached, the haemapo- 

 physes never. The outline, marked by six bases of as many 

 processes, is very remarkable, especially in the smaller bones, which 

 may well be called hexagonal, the height nearly equalling the 

 breadth ; while in the earlier vertebrae the faces are oval and broader 

 than high. 



The length of* the skeleton would appear, allowing for cartilage, 

 to be about 17*0 feet: viz. head, i foot 6 inches; neck, 4 feet 8 

 inches ; back, 5 feet 5 inches ; tail, 5 feet 5 inches. 



PLESIOSAURUS ELLIPSOSPONDYLUS. Owen. 



The Oxford collection contains a series of nine cervicals from 

 different individuals, and three anterior dorsals. All have trans- 

 versely elliptical, biconcave articulating faces, with pitted centres ; 

 the length is so much less than the height as to ally them to the 

 brachyspondylus species already described. The sides of the cervicals 

 are marked by strong prominent cicatrices ; the interforaminal space 

 below is convex, the surface furrowed. 



