SCOTT: ENTELONYCHIA OF THE SANTA CRUZ BEDS. 
275 
hardly visible from that side. The second phalanx is much more slender 
and but little shorter than the first, in marked contrast to Nesoclon, in 
which this bone is very short and wide. The proximal trochlea is 
divided by a median ridge into two shallow pits, and the distal one, which 
is feebly grooved in the median line, is remarkably extended, being reflected 
far over upon the dorsal side and, when seen in profile, describes nearly 
two-thirds of a circle. This gives to the phalanx quite the appearance 
of the corresponding bone in certain Carnivora. The ungual is much 
modified and has assumed the shape of a claw, somewhat as in Macro- 
therium and Chalicotherium of the European Miocene and in the North 
American Moropus , but the modification is less extreme and the departure 
from the ordinary ungulate type not so great. The phalanx is long, 
almost equalling the combined first and second in length, very rugose 
and cleft at the distal end, the cleft continuing as a deep groove of the 
dorsal surface for nearly half the length of the bone. The proximal 
portion of the ungual is very thick palmo-dorsally, this dimension 
exceeding the transverse, but the dorsal face is strongly curved and the 
thickness diminishes rapidly to the distal end. Proximally, there is a 
beak-like extension of the median dorsal line, but no conspicuous sub- 
ungual process. 
In the other digits the ungual phalanx differs somewhat in size and 
form. The arrangement made by Ameghino (which is followed in PI. 
XXX, fig. 1) gives the smallest of the unguals to digit II, but this is 
more probably referable to the pollex, while the one assigned to the latter, 
the broadest and heaviest of the entire series, should probably be trans- 
ferred to the fifth digit. In none of the digits is there visible any ten- 
dency to coossification of the phalanges, such as constantly occurs between 
the proximal and second phalanges of digit II in Moropus. 
The phalanges have an unusual degree of mobility upon the metacarpals 
and apparently could move through an arc of 180°. This but adds to 
the difficulty of understanding how the manus was used. The fact that 
in three continents three different orders of ungulates, the Artiodactyla, 
Perissodactyla and Entelonychia, should have acquired clawed feet, cer- 
tainly would seem to indicate a response to some general need, but no 
one has yet made any plausible suggestion as to what that need was, nor 
does any existing herbivorous mammal throw any light upon the problem. 
From the character of all the articulations involved, it is probable that 
