102 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



two elements in the middle of the carpus, a large cubical bone on the outer 

 side and a smaller on the inner. There are four bones in the distal row con- 

 nected with the metacarpals. The four bones in the proximal row may be 

 radiale, two intermedia, and fibulare, or they may be radiale, intermedium, 

 fibulare, and pisiform. The figures give the general form and relations. 



The metacarpals preserved are short and stout and the phalanges are of 

 similar form. Whole foot short and broad, with wide terminal phalanges. 



The pelvis and posterior limb (Nos. 4183, 4582 Am. Mus., plate 9) : The 

 pelvis is peculiarly frog-like in its general suggestion; the bones of each side 

 are closely united, and the acetabulum is closed. The ilium is elongate and 

 nearly straight, and the ischium and pubis are united by a wide and strong 

 symphysis. The ilium has the upper part prolonged into a narrow blade 

 with nearly parallel edges; the upper end is slightly thickened; on the pos- 

 terior edge, near the lower end, is a slight notch. In one specimen. No. 4183 

 Am. Mus., there are a few rugose pits at the point of attachment of the sacral 

 rib, but this is not noticed in other specimens. The pubis has the anterior 

 face thickened and widened, so that when the two bones of opposite sides 

 are joined there is a broad, flat surface facing anteriorly. This reaches as 

 far up as the center of the acetabulum. The pubic foramen is situated far 

 forward, just below the anterior edge of the acetabulum, and emerges on 

 the flat anterior face. The ischium is broad and thin, and projects posteriorly 

 beyond the ilium. The pubis and ischium stand nearly vertical, and the 

 symphysis is very narrow on the bottom line, not over i or 2 cm., but is 

 very wide vertically at the anterior end and narrower posteriorly. The 

 relation of the sacral rib, shown in three specimens, demonstrates that the 

 pelvis touched the ground only at the anterior corner of the pubis; the outer, 

 lower, edge of the symphysis is nearly straight, and in the natural position 

 of the pelvis was inclined upward and backward, but the inner, upper edge 

 is nearly parallel to the ground. This is the result of the symphysis being so 

 much broader at the anterior end. Because the pubis and ischium are so 

 nearly vertical, the aperture of the pelvis is very narrow. The acetabulum 

 is broad and very shallow, with slightly raised edges. This is most prominent 

 at the antero-inferior end, just over the pubic foramen. 



The femur (4193 Am. Mus.) is nearly straight with prominent, expanded 

 extremities. The proximal end is thickened on the inner side, round behind 

 and flattened anteriorly, but it lacks the deep concavity of the anterior face 

 present in the Pelycosaurs. The two edges of this flat face extend straight 

 downward for a few centimeters, and then converge and unite to form a high, 

 thin ridge with a convex edge, which extends to the articular face of the distal 

 end. The section of the middle part of the shaft is a sharp isosceles triangle 

 with the apex forward; this ridge is one of the most characteristic features 

 of the Eryops femur and renders it unmistakable. The distal face is par- 

 tially divided by a deep groove, the outer portion being much more prom- 

 inent than the inner. 



The tibia (No. 4893 Am. Mus.) : The upper end is expanded and very 

 imperfectly divided into two faces by a notch on the anterior border. The 

 whole surface is inclined slightly inwards. The shaft is suddenly contracted 

 below the head and has a triangular section. The lower end of the bone is 

 turned inwards, so that the lower face lies at an angle of about 45° to the 

 upper. This face is not divided into facets, but it is semicircular in form, 

 to permit it to articulate with more than one bone. 



