xn. PLESIOSAURUS. 309 



one-tenth of the diameter. The foramina are lateral. Transverse 



Diagram CXIV. Dorsal Vertebrae of PJesiosaurus Oxoniensis. Scale, one-fifth 



of nature. 



I. Seen from the front. 



2. Side view. 3. Posterior zygapophysis. 

 4. Seen from above. 



diameter of the largest, 2*75 inches; height, 2*5; length, 2*1. 

 They may be regarded as middle dorsals. 



Rifts. Portions have been found. One of a very great size must 

 have belonged to another species of animal not otherwise indicated. 

 They are of the usual form of middle dorsal ribs, with hardly a 

 mark of that division across the head which occurs in the cervical 

 ribs. The substance is largely cellular in the middle, more com- 

 pact toward the sides. 



Caudal vertebrae are exemplified by a series of eight, which appear 

 to be consecutive, and to indicate a rapid contraction of the size 

 of the tail, which must have been shorter than is usual in the 

 genus. Their lateral processes extend, from point to point, to about 

 twice the breadth of the vertebra. The vertebra nearest the end 

 have cicatrices on both the lower edges, those further forward on 

 the posterior edge only. 



