274 S. W. AVILLISTON NP:W GENERA OF PERMIAN VERTEBRATES 



In a future communication I shall give a similar comparative illus- 

 tration of the humeri of the reptiles, of which there are in the collections 

 of the University of Chicago 12 distinct forms, representing as many 

 genera. 



Radius (plate 14, figures 7-9). — The radius has a very slender shaft 

 in the middle, and is broadly and thickly expanded at either end. The 

 posterior border is nearly straight, the anterior deeply concave, the two 

 lateral borders nearly symmetrically and deeply concave in outline, the 

 extremities of nearly equal width and nearly transversely truncate. The 

 proximal end has a groove on the posterior side thinning the inner articu- 

 lar surface. 



Ulna (plate 14, figure 10). — The ulna is a remarkably slender bone 

 in comparison with the radius — slender in comparison with the bone in 

 other genera of Permian air-breathers. It has a slender and curved shaft 

 on the distal three-fifths, the distal extremity only a little widened, with 

 its greater diameter at right angles to the greater diameter of the prox- 

 imal end. The olecranon is very slightly produced, and the articular 

 surface for the humerus is oblique to both axes of the bones; the inner 

 side of the proximal end is flattened. 



Two bones of the proximal row of carpals with several phalanges were 

 found close to the bones of the left forearm. They are relatively small. 

 Their characters may be seen in the figures (plate 12, figure 3). 



PELVIC GIRDLE AND EXTREMITY 



Pelvis.— rThe pelvis (plate 12, figure 4; plate 13, figure 1) is very 

 strong and stout, the two halves meeting in a very firm symphysis, which 

 forms an obtuse ventral ridge most protuberant in the middle below the 

 acetabulum. The pelvic cavity is deep and spoutlike, nearly semicircular 

 in transverse outline, with the lateral margins anteriorly and posteriorly 

 slightly flaring. The anterior border is emarginate in the middle, the 

 sides convex in outline, with a notch. The posterior margin is slightly 

 narrower than the anterior, and has a deeper emargination in the middle 

 line, the sides somewhat thinner, with convex borders to the outer, some- 

 what angular margin. The posterior margin of each innominate is con- 

 cave from the upper angle of the ilium, with a pronounced angular pro- 

 jection in the middle of the concavity at the junction of the ilium and 

 ischium; this border is rather thin throughout. The front border is like- 

 wise concave throughout from the upper angle of the ilium, with a slight 

 convexity below the middle at the place of junction between the ilium 

 and pubis. This border is much thicker than the posterior, and flares 

 outwardly below. The acetabulum is deep and large, with its greatest 



