8 Watson, New Genera of Upper Liassic Plesiosaurs. 



There is no trace whatever of an interclavicle. 



This girdle at once shows that P. homalospondyliis is 

 not a Plesiosaurus but belongs to the " Elasmosauridae." 

 The scapula and clavicular arch strongly resemble those 

 of Cryptocleidus, they present, however, many differences 

 in detail. 



Viewed as a whole, the pectoral girdle of Microcleidus 

 differs from that of Cryptocleidus and most other Sauro- 

 pterygia in its great relative narrowness, which is rendered 

 still more striking by the lack of any lateral processes at 

 the hinder ends of the coracoid. 



The only Liassic genus yet described with an Elasmo- 

 saurian type of pectoral girdle is Eretmosanms, Seeley, 

 founded on Plesiosaurus rugosiis of the Lower Lias, and 

 also including E. dubius, Blake, of the Upper Lias. In 

 this genus the two pre-coracoidal foramina are very small, 

 and the clavicular arch is unknown. Microcleidus is quite 

 well distinguished from Eretvwsaurus by the characters 

 of the vertebral column, particularly by the elongated 

 cervicals and the very long neural spines of the dorsal 

 vertebrae. 



Pelvic Girdle. 



The material existing for the description of the pelvic 

 girdle of Microcleidus consists of the displaced and some- 

 what mutilated pubes and ischia of the Manchester 

 specimen, L. 7077, and the naturally associated and well- 

 exposed girdle which belongs to the skeleton in the York 

 Museum. 



These two specimens present some marked differences 

 in the pelvis ; so far as I could examine the York 

 skeleton, which, however, is fastened to the wall at the 

 back of a glass case which cannot be opened, all the 

 characters of the axial skeleton and of the pro-podial 



