32 BRITISH FOSSIL REPTILES. 



2 feet. It is much shorter in proportion to the trunk (as reckoned from the first 

 dorsal (ib., fig. 1, d) to last sacral (ib., s) than in the Plesiosaurus homahspondylus 

 (Tab. V), and differs in the more pro.ximal position of the metacarpal of the fifth digit, 

 and in the smaller size of the radial carpal of the distal row. 



Like the scapula in the pectoral arch, the ilium (Tab. IX, G2) is the smallest bone 

 of the pelvic one; it is 5 inches in length, I^inch across the obliquely truncate upper 

 (proximal or sacral) end, it contracts to a diameter of 9 lines at its middle, and then 

 expands to a breadth of 2 inches 4 lines, with proportional thickness, at its lower 

 acetabular end. The stem is subcompressed, convex transversely, and also longitudi- 

 nally at the upper half, which shows a low ridge externally, and is longitudinally 

 striate near the margin of the surface connected with the sacral pleurapophyses, from 

 which, as before stated, it has been dislocated. The acetabular end preserves its 

 natural connections with the corresponding thickened part of the ischium (ib., G3), 

 which on both right and left sides is interposed between the ilium and pubis. The 

 rough acetabular surface is nevertheless continued from the ischium upon the pubis, 

 for about two inches of the contiguous border. The head of the femur is applied to 

 the ischio-pubic surface in both limbs, yet the better proportioned articular depression 

 is that formed b)^ the ilium and ischium, from which it seems as if the femur had been 

 dislocated forward. As, however, the mode of attachment has been by a ligamentous 

 mass, this may have converged from the whole of the antero-posteriorly extended 

 acetabular surface to the head of the thigh-bone, allowing a certain freedom of play of 

 the bone forward and backvvard ; the diameter of such acetabular surface, lengthwise, 

 is 5 inches, the greatest vertical diameter is 3 inches. 



The ischium (Tab. IX, 63), as it passes from the acetabulum mesiad, loses its 

 thickness and expands into a plate of tlie usual triangular form, the posterior apex of 

 which is seen on the left side behind the two overlying sacral ribs, stretching as far 

 back as the ilium (ib., 62) ; from this apex, or angle, to the acetabular junction with the 

 pubis, the ischium measures 8 inches. Pyritic matter intervenes between tlie ischium 

 and sacral ribs, on the left side. 



So much of the pubis (Tab. IX, 64) as is visible on the left side exhibits the usual 

 subcircular discoid shape, with the two facets on the thickened part of the margin, one 

 for articulation with the ischium, the other completing the fore part of the acetabular 

 tract. The broadest part of the exposed pubic disk measures fi inches lengthwise. 



The femur (Tab. IX, Gj) is 9 inches 9 lines in length. A longitudinal notch 

 feebly marks out a trochanteric part of the thick, convex, articular head ; this is 

 coarsely pitted for the ligamentous insertions. The shaft contracts, chiefly losing 

 thickness, and becoming lamelliform as it expands in breadth to the distal articular 

 surface. This is convex, curving in a greater degree at its hinder part. Both anterior 

 and posterior borders of the shaft are concave ; the former least so, but to that extent 

 differentiating the femur from the humerus, in which it is straight, or rather convex. 



