I04 AMERICAN PERMIAN VERTEBRATES 



rygia. The ilium has a long, thin, and narrow process, directed 

 horizontally backward. Its upper margin is thin, crest-like, scarcely 

 projecting above the sacral ribs. The anterior superior border in 

 front of the sacral rib is thickened and rounded. Fully three-fifths 

 of the acetabulum is formed by this bone. It has a strong overhang- 

 ing ridge or process directly above the cavity. On the inner side 

 distinct facets are visible for the attachment of the sacral ribs, the 

 large one in front and below, the smaller one almost wholly on the 

 posterior process behind and above. The pubic and ischiadic 

 borders meet in a little more than a right angle. A little in 

 front of the angle on the inner side there is a vertical depression or 

 groove continuing upward the depression leading into the obturator 

 foramen. 



The pubes are remarkable for their large size and forward 

 extension. They are broadly expanded in front to the full width of 

 the pelvis, extending forward almost parallel with the plane of the 

 vertebral column above them. The two bones meet in a long, 

 nearly horizontal suture, leaving an angular emargination in the 

 middle behind where they turn downward into the true brim of the 

 pelvis. From side to side above the surface is convex, and the 

 surface below is concave transversely. The thickened lateral 

 borders turn downward from the pubo-ischiadic suture and inward 

 to the horizontal table, and then outwardly horizontally and 

 forward. In the middle behind the distance between the two bones 

 is narrowed to form a U, turning deeply downward into the narrow 

 trough formed by the two. ischia. The pubic foramen is a Httle 

 in front of the ischiadic border, piercing the bone vertically as the 

 continuation of the shallow groove beginning above the ilium. 

 The inferior orifice of the foramen is an oval opening of considerable 

 size situated in the angle between the descending flange and the 

 acetabular margin. 



The ischia are shaped very much like those of the long-necked 

 plesiosaurs, hatchet-shaped bones which descend to meet each 

 other angularly, considerably below the plane of the pubic expan- 

 sion, into which cavity the downward deflection of the posterior 

 borders of the pubes open. They are massive bones, the ace- 

 tabular border especially protuberant and heavy. The outer 



