624 WILLIAM R. SMELLIE ON 



iliac surfaces, and also in the posterior part of the neck. These mark the attachment 

 of the muscles which held the ilium in position. 



The ilium is a stout bone, and its lower end, bearing as it does the facets for the 

 acetabular surface and for the ischium, is greatly enlarged. The two jfacets are con- 

 tinuous with one another, but that for the acetabulum is turned up and prolonged 

 into a sharp lip with roughened borders. Practically the whole rim of the head 

 except the anterior inner side is roughened for muscle attachment. The shaft is 

 stout and roughly triangular in section in the proximal part, but flattens out to 

 conform to the spade-like form of the upper extremity. The anterior margin of the 

 bone is concave, but the posterior is slightly convex, with prominent tubercles in the 

 middle. From this point to the upper end of the bone rugosities cover both margins. 

 The end of the bone is greatly flattened from within outwards, and the surface is 

 smooth. The inner lip bears strong rugosities for muscle attachment, and the outer 

 margin and both sides of the bone also bear rugosities, but less conspicuously. These 

 would serve for the muscular attachment of the end of the ilium to the sacrum. 

 There are no indications that the ilium was fused to the ischium. 



Considering the whole pelvis in relation to the pelvic girdles of other Oxfordian 

 Plesiosaurs, differences are observed comparable to the changes found in the shoulder- 

 girdle. The pubes are very broad, and the great width between the antero-external 

 angles of the united bones is a repetition of the same feature found in the united 

 coracoids, and further emphasises the broad build of the animal. From the low angle 

 in which the two sides of each girdle meet in the mid-ventral line, it is evident that 

 the under side of the animal was almost flat. The increased rigidity due to the 

 peculiar ossification of the shoulder-girdle is reflected again in the pelvis — at least, so 

 far as the pubes and ischia are concerned. Along the median symphysis these bones 

 have been in contact for a great proportion of their length, and the pubis and ischium 

 of each side have been partially fused. With the ilium the case is different. As the 

 limbs were used habitually for the propulsion of the body through the water and not 

 for its support on land, the connections between the ischium and ilium and between 

 the ilium and sacrum were wholly ligamentous. Further, the ilium is directed back- 

 wards more than upwards, the whole arrangement being suitable for resisting the 

 tension set up at each drive of the paddle rather than for functioning in the support 

 of the weight of the body. 



Hind Limb. — The only bone of the hind limbs preserved is the left femur 

 (Plate, fig. 5). It resembles the humerus, and, though somewhat more slender, it 

 is only slightly shorter than that bone. The head is convex and rough, having been 

 capped with cartilage in life. It is oval in outline, with the long diameter running 

 antero-posteriorly. The surface of the head is continuous, through a wide (5 '5 cm.) 

 constriction, with the surface of the trochanter. The trochanter is large and roughly 

 rectangular in outline, and its surface is irregularly concave ; its posterior margin is 

 low. so that the trochanter has a decided slope to the rear. The outer surface is 



