39$ Williston — New Family of Reptiles from, the 



the groove for the ulna on the dorsal side. It is an interest- 

 ing fact that not only the structure of the humerus, hut also 

 the whole anterior limb, resembles, not only that of Diadectes, 

 but also that of the amphibian Eryops, suggesting similar 

 habits in all three animals, and possibly too genetic affinities. 

 There is a moderately stout ectepicondylar process, as in Des- 

 mospondylus, Seymouria, Diadectes, Eryqps, etc. It is situ- 

 ated a little below the lateral process on the radial side. 



Radius. Ulna. — The radius and ulna are very like those of 

 Diadectes and Eryops, rather short and stout bones. The two 

 lie in position on each side, as shown in the figure, the upper 

 end of the radius partly lodged in the lower end of the sig- 

 moid fossa, and the two are in one plane. The radius has the 

 capitulum truncated and hollowed for articulation with the 

 humerus, the extremity strongly convex on the dorsal, flat- 

 tened on the ventral side. The shaft of the bone is moderately 

 narrowed, and its two borders are nearly symmetrically con- 

 cave. The lower extremity is more expanded, with its end 

 truncate and flattened for articulation with the radiale and 

 intermedium, the inner side the thicker. Just above the inner 

 distal angle there is a characteristic protuberance, which evi- 

 dently came in close contact with the ulna. The ulna is a 

 more slender bone and is a little longer; it is thick and mas- 

 sive at its upper end, the shaft more slender than that of the 

 radius, and the lower end moderately expanded. Its radial 

 border is deeply concave, its inner border nearly straight to 

 the lower fifth. The sigmoid fossa is deep, winding obliquely 

 about the bone, and fits accurately the curved trochlear sur- 

 face on the distal and dorsal side of the humerus. Evidently 

 the elbow joint was a strong and firm one. The distal extrem- 

 ity of the ulna is subtruncate, its border somewhat oblique to 

 that of the radius, but with the angle broadly rounded for 

 articulation with the pisiform. Both radius and ulna have 

 the dorsal side convex, the ventral more flattened. 



Front Foot. — Lying in close articulation with the radii and 

 ulnae are the proximal carpal bones, four in number on each 

 side, the radiale, intermedium, ulnare and pisiform. The pisi- 

 form is a small bone, thinned along its free border and articu- 

 lating in its usual position between the ulna and ulnare. The 

 ulnare, the largest of the carpal elements, is an irregularly 

 oval bone, articulating rather broadly with the ulna and the 

 intermedium, but without distinct facets for the other carpal 

 elements. The smaller intermedium is much thickened, artic- 

 ulating with the ulna, ulnare and the radius, with a very small 

 free border between the ulna and the radius. The radiale 

 is the smallest of the three, almost vestigial in fact, elon- 

 gate-ovate in shape, with the radial border straight and flat- 



