276 THE BATE OOLITE PERIOD. CHAP. 



face meets that of middle breadth, seems to be partly original and 

 partly the effect of accident. 



The bone is 38*5 inches long, a little arched, and toward the 

 smaller end a little twisted (figs. I. and 3), so that the longest 

 diameter of that end, 7 inches, lies obliquely to the rest of the bone. 

 The shorter axis there is 5 inches. 



The pelvic girdle of the great reptile we are studying was formed 

 on a scale of grandeur somewhat difficult to realize. We possess 

 several bones which for some time were not at all clearly under- 

 stood : after much thought, and frequent comparisons of them with 

 skeletons of crocodiles and lizards, I arrive at the conviction which 

 is expressed in Diagram CIV. Half the pelvic girdle is there 

 drawn, as it presents itself to my mind, looking at the body from 

 beneath, the arrow flying from the head. The upper bone is the 

 pubis, measuring 38 inches between the extremes, with a breadth 

 of 15 inches in the middle, the greatest thickness 4 inches. The 

 whole is formed upon an arch ; the inner or posterior edge is on 

 a uniform curve, from which rises the medial symphysis s s, while 

 the other end is truncated to meet the ischium, at a, and form with 

 it the lower part of the acetabular socket. In this bone is an oval 

 foramen, f. The outer or forward edge has three facets; that 

 near f receives a process of the ilium, so that three junction 

 surfaces are recognized in the bone. The general figure is nearly 

 flat, with sweeping convexities along the middle. 



On comparing this bone with the corresponding part in fossil 

 reptiles, it is apparent that no special analogy is to be seen with 

 ichthyosaurus or plesiosaurus, teleosaurus or megalosaurus. Some 

 resemblance may be allowed to the pubic bones of living chelonians, 

 which vary considerably : very little definite likeness can be traced 

 when the comparison is made with crocodiles ; but closer and more 

 satisfactory affinity appears when we place together a reduced 

 drawing of the huge pelvic arrangement of ceteosaurus and the 

 tiny structure of a living monitor. Taking, for example, Regenia 

 ocellata, of which a fine skeleton is in the Oxford Museum, we 

 perceive a striking similitude ; see Diagram CIV. fig. 3. 



The small drawing referred to shews how much alike are the 

 little and the great bone similar concave sweep behind, similar 

 facets in front, corresponding symphysial terminations, a foramen 

 in the disk. 



