160 



MAEINE EEPTILES OP THE OXFOED CLAI. 



The /"org limh (text-fig. 77) is peculiar in several resjjects and differs considerably 

 from that of Cryptocleidus and of Murcenosaurus ; its most striking characteristic is 

 that the humerus articulates distally with four bones — three, the radius (r.), ulna {u.), 

 and pisiform [p.), being large, the fourth a small postaxial accessory ossicle {a.). 



The humerus (A.) is short and stout; the head is rounded in outline and convex ; at 

 its upper anterior border it is continuous with the surface of the strongly developed 

 tuberosity [Lp.). This is bounded both in front and behind by strong ridges, 

 which extend down a little on the shaft; its upper surface is flattened, and a little 



Test-fip;. 77. 



Left fore paddle (imperfect) of Trideidns seeleyi, from above. (Type specimeB, E. 3539, about j nat. size.) 



a., postaxial accessory ossicle ; h., humerus ; int., intermedium ; l.p., tuberosity ; 



mc.r., fifth metacarpal ; 2^., pisiform ; r., radius ; rad., radiale ; u., ulna ; uln., ulnare. 



below its upper border there is a well-marked rugosity for the attachment of muscle. 

 The stout shaft is oval in section ; its anterior border bears a roughened ridge, and the 

 upper part of its ventral and ventral-posterior surface is roughened for muscle- 

 attachments. Distally the bone is expanded and compressed from above downwards. 

 The facet for the radius is the largest, that for the pisiform the smallest ; the surface 

 for the accessory ossicle is situated entirely on the postaxial border nearly parallel with 

 the long axis of the bone. 



