﻿64 



FOSSIL REPTILIA OP THE 



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

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

 its syrnphysial end (ib., ff) 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 syrnphysial end, to the extent indicated by the dotted lines in PI. XX, fig. 1, the total 

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



§ 13. Pubis. — This bone (PI. XX, figs. 4 — 7) presents the type of the pubis in Lacer- 

 tians (ib., figs. 8 and 9) in the pectineal process (c), and the perforation (d) } 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. A Chelonian 

 character is shown in the length of the bone between the head («) and the process (c). 



The articular end (a) has been better preserved than the corresponding one of the 

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

 6 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 

 the proportion, if any, contributed by the pubis to the acetabulum must have been very 

 small, for no trace of such appears. 



The pubis as it recedes from this joint gradually narrows to a breadth of 3 inches 



4 lines, then more rapidly expands to form the perforated pectineal plate (c). This plate 

 or process becomes, as in Lizards and Tortoises, thickened and tuberous at its free 

 prominent border, which describes a bold convexity before subsiding into the slender 

 continuation of the pubis (<?,/). The margin of c continued thereto by the dotted line, 

 in figs. 4 and 5, is a fractured one ; and the angle of the border (<?) to which the dotted 

 line is continued shows also fracture ; the extension of bone along that line is inferential- 

 Proximad of such fracture the anterior border of the pubis is entire and sharp, a continua- 

 tion of that which partly circumscribes the oblique pectineal hole or channel (d). 



From the pectineal expansion the pubis contracts to a breadth of 2 inches, then 

 expands to its syrnphysial end (g), which, when entire, must have had a breadth of from 



5 to 6 inches. The abraded surface (ib., fig. 7) gives a fuller ellipse than that of the 

 ischium (ib., fig. 3), but, as in that bone, indicates a syrnphysial junction with the opposite 

 pubis. The hind border of the pubis (f) is rounded and thicker than the fore border (<?). 



The neural surface (ib., fig. 5) is feebly canaliculate lengthwise in part of its extent, and 

 this character is shown, though still more feebly, in the pubis of JJromastyx (fig. 9, 64). 

 But the accentuation of this surface in the broader half of the pubis of Omosaurus, as shown 

 in fig. 5, is due to crushing and fracture seemingly in relation to the original prominence 

 of the part of the pectineal process ( c , fig. 5), which has been pressed to flatness with 

 slight concavity. 



I conclude from the length of both ischium and pubis that they diverged from each 

 other, viz., from their outer to their inner or syrnphysial ends, at an angle nearer that in 



