12 Watson, New Genera of Upper Liassic Plesiosaurs. 



There are many points of resemblance between the 

 two girdles, but the York specimen differs from L. 7077 

 in the following ways : — 



1st. It is relatively much broader. 



2nd. The ischia are much shorter. 



3rd. There are two obturatores foramina separated 

 by a median union of the pubis and ischia. This 

 character may only depend on age. 



One character strongly brought out by the York 

 skeleton is that there is an angle of nearly 30° between 

 the pubis and ischium of the same side ; this bend, the 

 occurrence of which was a matter of inference in the case 

 of the Manchester specimen, is to be seen at York. 



The new genus Microcleidus may be defined as 

 follows : — Sauropterygia with a very long neck and small 

 sku.l' Cervical vertebrae elongated and narrow across 

 the zygapophyses, which have a fore and aft direction. 

 Dorsal vertebrae with constricted centra, transverse pro- 

 cesses wholely supported by the arch, and very high 

 neural spines. 



Column composed of 40 cervicals, 5+17 pectorals 

 and dorsals, 3 sacrals and 20-|-caudals. (These numbers 

 are probably liable to individual variation.) 



Cervical ribs double-headed and long, with a small 

 anterior projection. 



Pectoral girdle with reduced clavicular arch not con- 

 taining an interclavicle. Scapulae meeting each other and 

 the coracoids in the middle line. Postero-lateral angles of 

 the coracoids not produced. Pelvic girdle with long pubic 

 and ischiac symphyses and the ilia articulating only with 

 the ischia. 



Pro-podial bones only articulating with two bones 

 distally. Radius and ulna long when compared with 

 their condition in later species. 



