OPHTHALMOSAUEUS. 53 



anterior edge of a strong deltoid crest (d.r.), which extends somewhat obliquely down 

 the shaft to a point a little above the middle. The lower border (a.b.) is somewhat 

 convex and makes a right angle with the anterior face (Lb.). The whole of the 

 proximal end of the bone is greatly roughened by a series of irregular rounded 

 prominences, clearly indicating that in life there was a thick cap of cartilage which 

 seems also to have extended on to the summit of the deltoid crest. The appearance 

 of this cartilage-covered region is quite unlike the nearly smooth and fibrous-looking 

 surface of the shaft. 



The shaft is short and stout and is considerably contracted in the middle, at tlie 

 same time becoming compressed dorso-ventrally ; its preaxial border is a sharp angle, 

 while posteriorly it is more rounded. Distally the bone expands greatly, the long 

 axis of the expansion making an angle of about 45° with tlie longest axis of the 

 proximal end, as already described. The effect of this peculiarity is to give the bone 

 the appearance of having undergone slight torsion. 



In many specimens the ventral surface of the distal expansion bears near its 

 preaxial angle a prominent tubercle (pi'.), while on the dorsal surface nearly opposite 

 there is sometimes an even more prominent projection (;«'.') which may form a 

 blunt proximally-directed process. These projections seem to have served for the 

 insertion of the tendons of muscles ; but it is remarkable that in many large and 

 apparently quite adult specimens they are entirely absent, and not the smallest trace 

 of muscle-attachments where these processes should be can be detected. It is diificult 

 to suppose that this difference in the musculature can be a specific character, and it 

 seems more probable that the presence or absence of the powerful muscles indicated 

 by these processes was a secondary sexual character, a conclusion that is to some 

 degree supported by the occurrence of about equal numbers of the two forms. The 

 distal articular surface bears three distinct facets, each concave and covered w'ith 

 rugosities indicating the presence in life of a covering of cartilage. The anterior 

 or radial surface (r.f.) is smaller than that for the ulna and makes an angle of about 

 135° with it. The ulnar surface (?«./'.) is large and roughly quadrate in form, its upper 

 and lower borders being convex, the anterior and posterior being formed by slight 

 ridges separating it from the anterior (radial) and posterior (pisiform) facet (p.f.) 

 respectively. The posterior facet is much smaller than the others and sometimes not 

 very distinctly marked off from the ulnar surface ; it is triangular in outline and 

 articulates with the bone which is here called the pisiform, that element of the 

 proximal row of the carpus having apparently shifted back till it acquired a surface 

 of union with the humerus. In some specimens the posterior facet is so small and 

 slightly marked that it is clear that in these cases the pisiform was only just in 

 contact with the humerus. The articulation of this bone with the humerus is no 

 doubt correlated with the increasing breadth of the paddle, but the same end seems 

 to have been attained in other genera by different means. Thus in the fore paddle 



