128 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



equal width and nearly transversely truncate. The proximal end has a 

 groove on the posterior side thinning the inner articular surface. 



" Ulna (plate 23) : 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 diam-' 

 eter at right angles to the greater diameter of the proximal 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 21, fig. 3). 



"Pelvis: The pelvis (plate 22, fig. i) 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 

 emarglnation in the middle line, the sides somewhat thinner, with convex 

 borders to the outer, somewhat angular margin. The posterior margin of 

 each innominate is concave from the upper angle of the ilium, with a pro- 

 nounced angular projection in the middle of the concavity at the junction 

 of the ilium and ischium; this border is rather thin throughout. The front 

 border is likewise 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 great- 

 est concavity below its middle. It has a distinct and rather protuberant 

 rim, save at the upper posterior part. Its upper border on the ilium is 

 marked by a small but distinct process overhanging the concavity. The 

 lower margin on the ischium is very prominent, forming an angular pro- 

 jection to the full width of the bone, while the stout expansion of the pubis 

 in front limits the deepest concavity of the acetabulum. The shape of the 

 acetabulum would indicate that the chief pressure of the femur was directed 

 nearly horizontally and a little backward. The lower rim is nearly horizon- 

 tal, deeply concave anteroposteriorly, overhanging the almost horizontal 

 outer surface below. The pubes flare outward on each side in front from 

 a subangular line, running downward and inward through the inner ori- 

 fice of the obturator foramen to either side of the median emarglnation 

 of the front border. The triangular surface either side thus limited looks 

 at an angle of about 45 degrees upward from the horizontal position of the 

 pelvis and slightly inward, and is gently convex from side to side. The under 

 surface on the sides of the conjoined pelvis is nearly horizontal laterally, 

 descending in the middle into a broad obtuse ridge, broadest and deepest 

 a little in front of the middle. In front the downward curvature of the 

 pubes leaves a concavity, at the bottom of which is the external opening of 

 the obturator foramen, very near the middle of the pubis anteroposteriorly, 

 and opposite the greatest protuberance of the pubic margin, not far from 

 the border of the acetabulum. The front border of the pubes is roughened 



