EDENTATA OF THE SANTA CRUZ BEDS. 339 



Santa Cruz Megalonychidce, and simply concave ; the proximal facet for 

 the ulna is very small, not covering one third of the circumference of the 

 head, but quite extended proximo-distally. The proximal portion of the 

 shaft is compressed antero-posteriorly, much more than in Hapalops, and 

 the abrupt broadening, which in the latter occurs nearly in the middle of 

 the shaft, is very much nearer to the proximal end ; the bicipital tubercle 

 is very prominent and rugose. As a whole, the shaft is curved both 

 laterally^and anteriorly and quite closely resembles that of Megatherium, 

 while the suprastyloid tubercle is much less prominent than in the latter; 

 the carpal surface is narrower internally and less extended upon the 

 styloid process. 



The ulna is very like that of Hapalops. In Megatherium the olecranon 

 is remarkably short and broad and inclined backward from the plane of 

 the shaft, making the whole proximal end extremely massive, while the 

 distal end of the ulna is narrow, very thick and incurved. In Prepothe- 

 rium, on the other hand, the ulna differs from that of Hapalops merely 

 in its straightness and relative length. 



The manus (Plate LXI, fig. 3) is incompletely known, but the parts 

 preserved differ in many ways from the corresponding elements of the 

 Santa Cruz Megalonychidce, without displaying any very marked approxi- 

 mation to those of Megatherium. Of the carpus, only the trapezoid and 

 magnum have been identified ; the former is longer proximo-distally than 

 in Hapalops ; the dorsal face is broad, but toward the palmar side the 

 bone contracts almost to an edge ; the scaphoid facet is not regularly 

 saddle-shaped, but divided into two parts, the junction of which forms a 

 low ridge ; the distal facet for metacarpal II is similarly divided and on 

 the radial side extends almost to the scaphoid surface. Evidently, the 

 trapezoid had a more oblique position in the carpus than that of Hapalops. 

 The magnum is very different from that of the latter genus, the proximal 

 end rising toward the palmar side into a prominent head, almost as in 

 an ungulate, and the proximo-internal border is not produced upward 

 between the scaphoid and lunar, the lunar facet covers nearly the whole 

 proximal end, making the contact with the scaphoid more lateral than 

 proximal. On the distal end, the dorsal portion of the facet for metacar- 

 pal III is in two parts which meet nearly at a right angle ; the palmar half 

 is single, large and concave ; dorsally, the magnum has no contact with 

 metacarpal II, but the palmar extension overlaps the head of the latter. 



