XIII. 



PLEIOSAURUS. 



349 



A nearly circular pubis, of which two specimens are in the 

 Museum, one from G-arsington, the other from Shotover, is a piano- 

 undulate thin bone, 13 '4 inches in the greatest diameter, with two 

 thickened parts of the periphery, one (s) for the symphysis, the 

 other (i) for opposition to the ischium. The arc included between 

 the middle points of these surfaces is 72. The depth of the bone 

 at s equals 0-9 inches, at i = 2'Q ; the greatest thickness of the 

 bone about the centre being 1-3, and the least, at the edges, 0*3. 

 The ossification from the centre is marked by abundance of radiating 

 grooves (Diagram CXLIIL). 



Diagram CXLIIL Pelvic bones of Pleiosaurus. Scale one-tenth of nature. 

 Arrangement of pubic bones (above), and ischial bones (below). 



A somewhat three-cornered broad thin bone, with an un- 

 dulated surface, and a central point of fibrous ossification, usually 

 regarded as an ischium, is represented in Diagram CXLIII. It is 

 a solid smooth bone, formed in three curves, two convex and one 

 concave. The symphysis is very short, curved, and cut at an angle 

 of 70 ; its depth being 1-25 inch. The anterior face of the bone is 

 strongly marked for cartilaginous adherence ; that part where the 

 femur was articulated being 3*35 inches deep. The longest 

 diameter 13-5 inches ; articulating surface, 3*75 ; anterior curve, 

 4*5. There is another specimen less complete, about one-fifth 

 larger. 



