296 DR. C. W. ANDREWS ON A NEW PLESIOSATJR [vol. Ixxviii, 



be referred to a second genus, Leptocleidus, its specific name 

 being Leptocleidus superstes. Probably Flesiosaurus 

 capensis is also referable to this genus. 



The relationship of Leptocleidus to the other Wealden genus 

 Brancasaurus, if Wegner's account of the shoulder-girdle is correct, 

 must be remote, since in the latter the scapula) extend inwards and 

 join the anterior prolongations of the coracoids so that the shoulder- 

 girdle is of Elasmosaurian type : it seems, however, by no means 

 impossible that Wegner's restoration of this region may be mistaken. 



The dimensions of the shoulder- girdle of Eurycleidus arcuatus 

 (in millimetres) are : — 



Greatest length in the middle line 558 



Coracoid. 



Length of coracoid , : , 456 



Width of coracoid at the glenoid cavity 211 



Width of the anterior prolongations 87 



Length of the glenoid surface 87 



Scapula. 



Length of the body of the scapula 280 



Length from the top of the dorsal ramus to the anterior end, about 244 



Width of the middle of the dorsal blade 53 



Clavicular arch. 



Greatest width 359 



Width of the interclavicle about 261 



The dimensions of the clavicular arch of Llurycleidiis mega- 

 cepJiahts (in millimetres) are : — 



Greatest width 464 



Width of the interclavicle 324 



Length in the middle line 153 



The humerus of Leptocleidus (PI. XV, fig. 4) was much 

 expanded distally, but seems to have articulated with the radius 

 and ulna only. The anterior border of the bone is nearly straight, 

 the posterior strongly concave. The upper surface is gently 

 concave in the direction of the long axis, the ventral face being 

 correspondingly convex. None of the other bones of the paddle 

 are preserved. 



The dimensions of the humerus (in millimetres) are : — 



Length 245 



Widthofhead 50 



Width of upper end, with trochanter 62 



Width of middle of shaft 60 



Width of distal expansion 124 



The chief interest of Leptocleidus superstes lies in the circum- 

 stance that, although of Wealden age, it has retained a very 

 primitive type of structure of the shoulder-girdle, similar to that 

 found in the Lower Liassic species Eurycleidus arcuatus and 

 E. megaceplialus. In all these the clavicular arch is large, and the 

 ventral rami of the scapulae remain widely separated in the middle 

 line. This type of shoulder- girdle is probably a direct inheritance 

 from the Triassic ancestors of the group. The tendency to the 

 reduction of the clavicular arch and its functional replacement by 

 the expansion of the scapulae to form a median symphysis was 



