Manchester Memoirs, Vol. Iv. {\(^\\) No.\i&. 7 



spine of the interclavicle can only imply the presence of a 

 pair of small blood vessels, probably supplying muscles, 

 passing upon each side of the interclavicle and persisting 

 even after the backward growth of the clavicles had en- 

 closed them ; in any case they represent the first 

 appearance of the interclavicular foramen, which is found 

 in so many later plesiosaurs. 



The whole girdle is of interest for its close resemblance 

 to that of Sthenarosaur?cs, where also we find a T-shaped 

 interclavicle, much more modified, however, than in this 

 case, together with widely separated anterior rami of the 

 the scapulre, and a comparatively narrow clavicular arch. 

 These two cases and PIcsiosanrHS ccviybcari are, in fact, 

 the only ones in which the clavicles do not extend back 

 on to the dorsal surface of the coracoids. The furcula of 

 Plesiosaurus arcuaUis, which is generally quoted as shewing 

 a similar condition, is damaged, a similar bone in the 

 British Museum (Natural History) and the conditions in 

 the type specimen of the very closely allied Plesiosaurus 

 megacephahis, shew that there was really a very delicate 

 posterior extension of the clavicles meeting the coracoids. 



