358 THE PORTLAND OOLITE PERIOD. CHAP. 



proximal end; thickness in the middle of the distal end, 2 '5. 

 Taking length at 100, the breadth = 37-5, thickness = 7-4. 



PLEIOSAURUS GAMMA. Owen. 



In the Oxford Museum are specimens of cervical, dorsal, and 

 caudal vertebrae which belong to a definite species found in the 

 Oxford clay of Weymouth, and in the Kimmeridge clay of 



n 



Diagram CLII. Cervical vertebra of Pleiosaurus gamma. Scale one-fifth of nature. 

 i. Seen from above. 2. Seen sideways. 3. Seen from below. 4. Seen in front. 



Shotover. One of the cervical specimens has at some time 

 received from Professor Owen the label ' gamma/ to which letter 

 some resemblance may be imagined in the boundary lines of the 

 lower cicatrices. 



These cervical vertebrae appear to be as short in proportion to 

 the other dimensions as that species which was named by Owen 

 P. brachydeirus, and shorter than any other species yet mentioned 

 in this vicinity. 



The length being 1-20 inch, breadth 3-05, and height 2'6o, the 

 proportions (TOO, 254, 217) agree fairly with those from Shotover 

 referred to P. brachydeirus. 



They differ in form, by an apparent straightness of the lower 

 edge, caused by the very low position of the cicatrices, which are 

 almost triple, the middle one deeply excavated. The articulating 

 faces are gently and uniformly concave round the deeply pitted 

 centre, and rounded at the edges. 



