336 A NEW MYLODON. 
expands to an extreme width of 117 mm., with a median ridge which begins at a 
point about half way on its length and widens into the roughened distal end. 
The terminal surface has two chief articulating faces, one concave, the other 
smaller and convex, for the reception of the carpals. The total length of the 
radius is 290 mm. or practically the same as in M. robustus. 
The bones of the fore feet are not all preserved, but most of the metacarpals 
and phalanges are represented. These seem to be nearly identical with those 
of Owen’s species, but are a trifle larger and slenderer. Digits 1, 2, and 3 were 
provided with powerful claws; digits 4 and 5 were clawless, and terminated in 
blunt, rounded ossicles. The first ungual phalanx (Plate 3, fig. 10) measures 
90 mm. in extreme length and differs from the others in having a stem some 
25 mm. in length, the long axis of which is bent at an angle with that of the claw- 
bearing portion. This angle seems much greater than in M. robustus. The 
proximal face is slightly concave. The bony core of the claw is some 55 mm. 
long, laterally compressed, and regularly tapering in side view to a blunt point. 
The basal half is surrounded by a thin bony sheath which becomes much thick- 
ened and rugose at the base ventrally (Plate 3, fig. 10). 
The second ungual phalanx (Plate 3, fig. 9) is without a stem-like proximal 
portion, but the base articulates directly with the next phalanx by means of 
two concave facets which are contiguous in the median line, and have their 
greatest length in a dorso-ventral plane. The sheath at the base of the bony 
core is extensive, some 45 mm. long laterally. The bony core of the claw is 
90 mm. long, slightly decurved, with a thickness from side to side of 26 mm. 
near the middle. It tapers abruptly to a blunt and rather flattened point. 
An angular ridge marks off the flattened ventral surface of the claw. The 
phalanx next proximal to this is short, 53 mm. long, with two rounded facets 
anteriorly, and a broadly concave facet posteriorly. On each side of the latter, 
at its ventral corners, is a small squarish facet which evidently articulated with 
a sesamoid. 
The third clawed phalanx (Plate 3, fig. 8) is extraordinarily large and power- 
ful, 180 mm. in extreme length. It is shaped in general like that of digit 2, except 
that it is more faleate and its inner side has a broad and shallow sulcus beginning 
near the summit about half way to the point and increasing in breadth and depth 
to the tip, which it entirely encompasses. The ventral pad for the attachment 
of tendons is broad, rounded and flattened, about 78 mm. in length from the 
proximal border of the phalanx. Dorsally the bony sheath extended at least 
63 mm. from the base of the claw, and thence forward and downward to the apex 
