AND PELVIC BONES OP PLIOSAURTTS EVANSI. 723 



and imperfect internally, where it is very thin and extends further 

 forward than the outer part of the bone. 



The median sutured surface is greatly thickened anteriorly, being 

 about 2± inches thick, while for a length of about 11 inches it is bent 

 into a remarkable rounded Y-shaped fold (c, & fig. 9), having the 

 bone thickest in the middle and compressed anteriorly and posteriorly. 

 The convexity of this fold I suppose to have been directed inward ; 

 it rises about 5| inches above a base-line. The crest of the fold is 

 5 inches from the most anterior part of the bone. 



The shape of the bone is very similar to that of the coracoid bone 

 in Murcmosaurus ; and this influenced me in hesitating to identify it 

 as the ischium. But I am acquainted with no coracoid in which 

 there is such a fold of the bone in the median suture, while I have 

 noticed some approximation to such a condition in the ischia of 

 certain Plesiosaurs ; and, although not very conclusive, this seems 

 to me more important than the form of the bone. On the other 

 hand, the bone is not paralleled in shape by any known Plesio- 

 saurian ischium, and is quite unlike an ischium from the Kimmeridge 

 Clay of Ely which I attribute to Pliosaurus. Being found close 

 together, there would seem to be an a priori probability that the two 

 expanded bones described should belong to the same animal, and to 

 the same region of the body ; but then the pubic and ischiac bones are 

 not the elements which would be expected in association with the 

 anterior portion of the vertebral column which is preserved. I have 

 no doubt that they are not the two bones of the pectoral arch ; but 

 the form of the coracoid in Pliosaurus may sometimes have been so 

 similar to that of the ischium as to justify the slight doubt which 

 this account of the bone implies. 



Professor Philips, in his ' Geology of Oxford ' (p. 350), with great 

 boldness has attempted a restoration of the pelvis of Pliosaurus, 

 which seems to me to be in the main correct, the forms attributed 

 to the bones being not dissimilar to those here described. 



