1J0 MAEINE EEPTILES OF THE OXFOED CLAY. 



the anterior border forms a prominent ridge, which is continued backwards as the 

 upper rim of the concavity which occupies most of the outer face of the ilium. The 

 roughened surface of the thickened antero-ventral angle is continued on to the ventral 

 border, where it narrows and is deeply notched. The portion of the surface behind 

 the notch, no doubt, was connected with the upper surface of the pubic process of the 

 ischium ; but its anterior portion, which is relatively much larger than in the modern 

 Crocodiles, probably, in part at least, supported the upper end of the pubis, which in 

 these Crocodiles does not appear to have united with the lower surface of the 

 pubic process of the ischium, as in recent forms. At least, there is no facet for 

 such a union, and the form of the antero-ventral portion of the ilium makes it 

 very probable that it was largely concerned in supporting the pubis. Thus, in the 

 Steneosaurs at least, although the pubis (pu.) is excluded from the acetabulum (acet.), 

 its relation to the other pelvic bones is more normal than in modern Crocodiles, and 

 there does not seem any reason to regard this bone in the Crocodilia as other than 

 a true pubis, which has been displaced by the development of the pubic process of the 

 ischium. The facet on the ilium for union with the main body of the ischium is separated 

 from the facet for the pubic process of that bone by a short interval ; in form it is 

 roughly crescentic, the concavity being external and the anterior limb of the ciescent 

 much narrower than the posterior, which forms a strong ventral prominence. Behind 

 this the posterior border of the bone is at first concave, then convex, passing at a sharp 

 angle into the superior border. Above the ischial surface there is a smooth acetabular 

 facet (acet.) which passes above into a well-marked depression, which forms the deepest 

 part of the general concavity of the outer face of the bone. The inner (sacral) face 

 (text-fig. 44) is smooth and gently convex from above downwards to about the level of 

 the lower end of the anterior process. Below this it is greatly roughened by the two 

 complex surfaces for union with the outer ends of the sacral ribs (sacs. 1, sacs. 2). Of 

 these surfaces the anterior one is roughly kidney-shaped, with a short strong ridge 

 projecting downwards and forwards from its upper edge. The posterior surface is 

 rather less rounded, and from near its upper end a prominent ridge runs upwards and 

 backwards to the posterior angle of the bone; this ridge fits into a corresponding 

 groove in the outer end of the backwardly directed flange of the second sacral rib. 

 Beneath the surface for the sacral ribs the bone is nearly smooth and gently convex. 



The ischium (PI. VII. figs. 7, 7 a ; is., text-figs. 43-44) is of the usual Crocodilian form. 

 Yentrally it is expanded into a broad triangular plate, the lower edge of which bears a 

 roughened sutural surface for union with its fellow of the opposite side (sym.). The 

 anterior angle is usually very acute, the posterior one is truncated. Above this expanded 

 portion the bone narrows to a neck, the width of which varies considerably in the 

 different species. Above this again is the bifurcated and thickened head, the posterior 

 portion of which is much the larger and bears at its upper end a large smooth facet 

 looking upwards and outwards (in the natural position of the bone), and forming the 



