A NEW MYLODON. 309 
The clavicles are broken, but the portions articulating with the acromion 
are present. This articulation was by a convex facet slightly constricted off 
from the shaft of the bone, and elliptical in outline. The shaft is elliptical in 
section becoming slightly flattened, and apparently more slender than in M. 
robustus. 
The humerus is essentially similar to that of M. robustus, but is perhaps a 
little smaller as nearly as can be determined in its shattered condition. In side 
view the head is nearly hemispherical, but from the dorsal aspect is seen to 
have the condylar surface mainly on its inner half and tapers anteriorly to con- 
form to the general outline of the glenoid cavity of the scapula. Its longest 
diameter is 111mm. The great development of the deltoid crest in M. robustus 
is seen likewise in this species. The pectoral crest seems to be less pronounced. 
From the trochin to the distal end of the deltoid rugosity is 275 mm., against 
about 256 in Owen’s species. From the latter point to the tip of the rounded 
portion of the condyle is about 155 mm., giving a total length of about 430 mm. 
for the entire humerus. Owen gives about 445 for M. robustus. The distal 
end has the same peculiar articulating surface, the outer half rounded, more than 
half a circumference in its anteroposterior extent, the inner half nearly flat. 
The entire articular surface is 125 mm. in transverse extent, which is about as in 
M. robustus. 
The ulna is represented by the proximal portion only. The most striking 
difference in comparison with MJ. robustus is the greater length of the supe- 
rior, flattened articular surface which is much longer than broad (diameters 
97 < 55 mm.), instead of about as broad as long; while the inferior concave 
articulation is likewise proportionately narrower and is actually separated from 
the superior facet. A deep depression lies between the two. This inferior articu- 
lating surface is contiguous anteriorly with a smaller one, nearly round and 
flattened in the frontal plane, that serves for articulation with an elliptical facet 
at the proximal border of the radius. The ulnar has therefore three distinct 
articulating facets at the proximal end, two for contact with the humerus and 
one for contact with the radius. To judge from Owen’s figure of Mylodon ro- 
bustus the radial facet seems to be distinct from that for the humerus instead of 
confluent with it. 
The radius is similar to that of M. robustus in size and shape. The proxi- 
mal end is an elliptical concave facet, whose diameters are 71 and 50 mm. re- 
spectively, for articulation with the humerus. On the ventral border of this 
is the small elliptical articulation for the ulna. Distally the radius gradually 
