2 2 PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



is longer and higher, and the foramen is smaller. The humerus of the specimen 

 of D. phaseolinus, with which this specimen was compared, is actually larger and 

 the foramen actually smaller, increasing the relative difference. In this specimen 

 the entocondylar process of the right humerus is slightly distorted, the upper edge 

 running obliquely downward from the shaft to the lower end; but on the left 

 humerus, which is undistorted, it passes out from the shaft more directly and there 

 was a long, somewhat oblique, inner edge to the process. On the lower corner 

 of this process there is a deep pit for the attachment of a ligament. 



On the back of the bone directly opposite the articular surface for the radius 

 is the strong ectocondyle, similar to that on the humerus of D. phaseolinus. The 

 position and large size of the ectocondyle, directed prominently backward and 

 even inward from the plane of the distal end, seem to be correlated with a powerful, 

 thickset humerus, short fore-arms, short, flattened feet, and especially with non- 

 acuminate ungual phalanges. It is the condition found in Eryops and Trematops 

 among the amphibians, Ophiacodon among the pelycosaurs, Limnoscelis, Dia- 

 dectes, Diasparactus, and Seymouria among the cotylosaurs. Williston found the 

 digits more slender in Seymouria, but no indications of acuminate claws have been 

 found in that genus. The great development of these processes for the attachment 

 of the extensor and supinator muscles on the outer side, of the flexor muscles on the 

 inner side, and the great mechanical advantage these muscles must have had, are 

 certainly correlated with a powerful manus; but the structure of the arms and 

 hands in the Captorhinidce is like that of the more cursorial structure found in 

 other pelycosaurs and cotylosaurs, and indicate widely different habits for this 

 group of Cotylosauria. 



The face for the radius is semicircular in form, with the lower, inner, border 

 truncated; the articular surface is flat or even concave, indicating the presence 

 of a large amount of cartilage and differing notably from the same face on the 

 humerus of the pelycosaurs, where it is strongly convex. As the face has the same 

 appearance on the bones from both sides it must be regarded as natural, but may 

 be merely ontogenetic in character. The face for the ulna is elongate and oblique 

 in position, passing from within outward and downward. It is largely confined to 

 the distal end of the bone, appearing only slightly on the lower, anterior, face, and 

 not at all on the upper, posterior. 



The ulna resembles that of D. phaseolinus, but is proportionately longer and 

 more slender, without such heavy extremities and without the accompanying 

 rugosities. The shaft is wide but thin. The upper end has an oblique, nearly 

 flat, slightly twisted, articular surface for the humerus; it was simply applied to 

 the corresponding face of that bone and did not embrace it, as in the pelycosaurs. 

 The lower end is a little expanded and presents two articular surfaces lying at 

 less than a right angle to each other and not separated by any non-articular space. 

 They are set at such an angle with the flat surface of the bone that they look more 

 inward than directly downward. The distal end of the shaft is curved inward 

 slightly at the lower part, increasing considerably the effect just mentioned. Viewed 

 from the posterior edge, the bone has a slight but very evident sigmoid outline. 



The radius is shorter and heavier than the ulna; the shaft is triangular in 

 section, with the thicker portion on the ulnar side. The proximal end is expanded, 

 with a semicircular face truncated on the posterior side. The articular surface is 

 gently concave; this concave face opposed to the concave face on the humerus 

 indicates the presence of a large amount of cartilage in the joint. The distal end 

 is elongate laterally, but rather narrow antero-posteriorly. There are two faces; 

 a short inner face, which, in connection with the oblique face on the inner side of 



