84 REPORT— 1839. 



certainly determined until some perfect specimens are met 

 with. 



From the same member of the upper oolite system, and from 

 the same locality, Shotover, Lord Cole possesses a well-pre- 

 served large triradiate flattened bone, which, from its corre- 

 spondence in colour and grain with the humeri and femora 

 above described, seems unquestionably to belong to the same 

 species of Plesiosaurus, of which it represents the scapulo- 

 clavicular bone. 



The longest diameter of this bonr, viz. from the end of the 

 ray representing the scapula to the sternal end of the clavicle, 

 is nine inches. The breadth of the scapular ray is three and 

 a half inches ; both this ray and the one representing the ster- 

 nal end of the clavicle are much flattened, not exceeding half 

 an inch in thickness : the third ray, which represents the hu- 

 meral end of the scapula and clavicle, is short and thick, and 

 terminates in a rough convex articular surface, part of which 

 joins the coracoid, and the rest contributes to form the glenoid 

 cavity for the humerus. The external and internal surfaces of 

 this bone are pretty smooth, but exhibit the lines or striae of 

 growth, which radiate from the centre of the bone. 



Near the place where the above- described bones were de- 

 posited, there was also found an ischium so closely corre- 

 sponding with them in size, colour, surface, and general con- 

 dition, as to leave little doubt of their being parts of the same 

 species if not individual. The length of this bone, taken be- 

 tween the two extremities of its median margin, is twelve 

 inches ; the distance from the anterior of these margins to the 

 anterior edge of the acetabular surface four inches. As this 

 bone confirms the indications of the specific difference of the 

 Plesiosaurus under consideration, a few words as to its modifi- 

 cations in other species may here be useful. The median mar- 

 gin of the ischium in the PL Hawkinsii, e. g., is straight, and 

 is joined to that of the opposite bone, except at the angles, 

 which are rounded off. 



in the PL dolichodeirus only the upper half of the corre- 

 sponding margins of the ischia are sufficiently straight and pa- 

 rallel to be in contact ; the lower half of the median margin of 

 each bone receding from its fall in a gentle convex line. 



In the PL brachycephalus the whole contour of the median 

 margin of the ischium is convex, but least prominent at the 

 middle part. In the present large species the corresponding 

 margin is still more convex, so that it could only come in con- 

 tact with the opposite ischium at one point of this margin. 



The anterior concavity, which cooperates with the pubis in 



