PELONEUSTES. 



59 



a little in front and behind, where probably cartilage was interposed between them. 

 The anterior border is concave, and forms the posterior margin of the obturator 

 foramen. The outer border is gently concave, while the posterior end is rounded. 

 The line of the ischial symphysis in the sagittal plane makes a very obtuse angle with 

 that of the pubic symphysis, so that the visceral aspect of the complete pelvic symphysis 

 is convex dorsally in a longitudinal direction, while ventrally it is concave (text-fig. 26). 

 The ilium (text-figs. 24, 25) consists of a much-expanded upper portion, a constricted 

 shaft, and a massive articular head. The expanded upper portion varies in form to a 



Text-fig. 24. 



cet. 



acetf. 



Pelvis of Peloneustes philarchus : A, pelvis from above ; B, left ilium from inner side. 



(E. 3318, \ nat. size.) 



aeet , acetabulum ; aest.f., acetabular surface of ilium ; il., ilium ; is., ischium; is.f., ischial facet of ilium ; 

 obt.f., obturator foramen ; pu., pubis ; sacs., surface of ilium for sacral ribs. 



remarkable degree ; probably this variation is the result of a varying degree of ossi- 

 fication of a cartilaginous upper border, but it is possible that when we know the 

 skull of the animal to which the ilium shown in text-fig. 25, B, belongs, it may be 

 found to be specifically different from P. philarchus. In undoubted specimens of 

 this species (text-fig. 25, A) the upper end of the ilium is much more expanded than 

 in any of the Elasmosauridae. The upper border (cr.i.) is convex and passes into the 



