SCOTT: ENTELONYCHIA OF THE SANTA CRUZ BEDS. 
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or ulnar, border of the bone very much shorter than the internal, reversing 
the proportions seen in Nesodon, in which the internal border is a mere 
angle. The distal end is occupied chiefly by the facet for me. IV, that 
for the larger and heavier me. V is more lateral than distal. The internal 
border is nearly straight, the facets for the magnum and me. Ill lying in 
almost the same vertical plane. 
The metacarpus is incompletely known, inasmuch as only me. Ill is 
represented by an entire specimen, but parts of all the others are also 
preserved. This metacarpus is totally different in character from that of 
any other known Santa Cruz ungulate: (1) It is pentadactyl, all the 
digits complete and functional ; (2) the symmetry is not mesaxonic, for, 
though me. Ill is symmetrical in itself, the two parts of the manus result- 
ing from the vertical bisection of digit III are by no means equal, the 
outer part preponderating, which is chiefly owing to the large size of me. 
V, the heaviest and, very possibly, the longest of the series ; (3) there is 
very little interlocking of the metacarpals ; (4) the distal trochlea is 
altogether exceptional. 
The first metacarpal, represented only by the proximal half, is the most 
slender of the series. As figured by Ameghino (’94^, 254, fig. 3) the head 
is placed considerably below that of me. II, with which the trapezium 
articulates laterally. There is a possibility of error in this arrangement, 
but unfortunately, my attention was drawn to this question too late for a 
re-examination of the originals. The second metacarpal, likewise known 
only from the proximal portion, differs notably from the shape seen in 
Nesodon and in the three- and four-toed perissodactyls, in having no pro- 
cess which overlaps the head of me. Ill to articulate with the magnum. 
This articulation is present, but it is vertical and lateral, the head of me. 
II rising above that of me. Ill, but not extending over it. The third 
metacarpal is remarkably long and straight and relatively slender; the 
proximal end is narrow, but little wider than the shaft, and bears an 
oblique, saddle-shaped facet for the magnum, which is slightly concave 
transversely and strongly convex palmo-dorsally. On the radial side of 
the head is a narrow, curved facet for me. II, which extends over the 
entire dorso-palmar thickness, and on the ulnar side a very large, vertical 
and nearly plane surface for the unciform, but this connection is lateral 
only and there is no process extending over me. IV, such as occurs in 
most polydactyl ungulates. On the dorsal face near the ulnar border is 
