362 



THE PORTLAND OOLITE PERIOD. 



CHAP. 



PLEIOSAURIAN AND PLESIOSAURIAN FEMORA, HUMERI, 

 AND PHALANGES. 



Of these the clay pits of Shotover, Wheatley, and Cumnor have 

 yielded a considerable number, and they seem to belong to several 

 species ; but to which of the species respectively mentioned in 

 the preceding pages is for the most part uncertain. Besides the 

 veiy large limb-bones of Market-Rasen (Diagram CXLVL), we 

 have several others of different sizes and forms, represented in 

 outline in the following diagrams. 



To distinguish femora and humeri is not always easy ; the best 



Diagram GLIX. Femur of Pleiosaurus macromerus. Scale one-tenth of nature. 



rule, as it appears to me, derived from a study of the complete 

 skeletons of plesiosaurs in the lias, is to regard those as humeri 

 which have the distal articulating faces very unsymmetrical, and 

 the anterior and posterior outlines very unequally curved. 



The proximal extremities vary much, some being nearly spheroidal, 

 others marked by a double-curved slope, others bicipital through 



