574 BRITISH FOSSIL REPTILES. 



nilotica, e.rj., the ilium is prolonged in front of the acetabulum to an extent equalling 

 only that of the acetabular excavation of the same bone. 



Ischium. — This bone (PI. 72, 63, and PI. 73, figs. 1 — 3) offers the structural type of 

 that in Chelonia and certain Lacertilia {TJromastyx, e.g., PI. 73, figs. 8 and 9, 63), in its 

 ' tuberosity ' or })osterior process (c) ; l)ut, in its slenderness or relation of breadth to 

 length, it exceeds that in any Lacertian or otlier (to me) known forms of existing Reptile. 

 Of the iliac articular end of the right ischium but little is exhibited, the bone (63, 

 PI. 72) having been pressed forward and behind the part of the acetabulum from 

 which it has been dislocated. The process (c) answering to that so marked in 

 TJromastyx, in the more perfect left ischium (PI. 73, fig. 8), comes off nearer the 

 articular end than in the Lizard. The rest of the bone is simply styliform and straight, 

 having no process crossing, as in Birds, the obturator interspace between ischium and 

 pubis. The smooth concavity on the under or haemal surface of the expanded end, 

 articulating with the ilium, contributes about a fourth part of the cavity for the head of 

 the femur. The end of the process (e) is rough, thickened, of an elongate subtriedral 

 form, 2^ inches by 1 inch ; the opposite or fore-end of the expansion has a 

 rough syndesmotic surface for the attachment of a similarly roughened end of the 

 pubis. The breadth of the ischium, including these processes, is 13 inches; from 

 this part the bone quickly contracts to a narrow plate. The hind margin of this plate 

 (ib., fig. 1, e) is moderately thick and rounded, whence the bone thins off to an edge in 

 front (ib., /). The haemal surface is flat or feebly concave, transversely, and is smooth 

 (PI. 73, fig. 1). The upper or neural surface is, transversly, rather convex, save where it 

 extends upon the acetabular part (a, ,i), and here it is rather concave. The body of the 

 Ijone gradually contracts to a breadth of 2^ inches; it then slightly expands to 

 its symphysial end (ib., 9, and fig. 3), which has a breadth of 4 inches, with a thickness 

 of 2 inches. Restoring a part wanting between the preserved body of the ischium and 

 the symphysial end, to the extent indicated by the dotted lines in PI. 73, fig. 1, the total 

 length of this pelvic bone in Omosaurus would be 2 feet 6 inches. 



Pubis. — This bone (PI. 73, figs. 4 — 7) presents the type of the pubis in Lacertians 

 (ib., figs. 8 and 9) in the pectineal process (c), and the perforation (rf), but adheres to 

 the Crocodilian type in presenting one articular surface only at the proximal end (a) for 

 the ischium, and (seemingly") contributing no share to the acetabular cavity. AChelonian 

 character is shown in the length of the bone between the head (a) and the process (e). 



The articular end {a) has been better preserved than the coriesponding one of the 

 left ischium (ib., fig. 1). It presents a narrow, elongate, synchondrosal, roughish facet, 

 C inches in length, 1 inch 7 lines in breadth, with a moderate convexity in the long axis 

 (ib., fig. 6). The posthumous abrasion of the articular surface checks an absolute state- 

 ment as to the precise configuration of this ischio-pubic joint in the recent Omosaur, but 



