344 A NEW MYLODON. 
equal openings, the anterior 25 mm. in advance of the posterior and some 15 mm. 
in long diameter, with a very small third opening (4 mm. in diameter) below and 
between these two. In the other specimen on the contrary, the three openings 
are in a row, the anteriormost large, the two others small. Further, the sym- 
physis of the Oregon specimen is about 109 mm. long or some 15 mm. shorter 
than in the Nebraska species, and there is at its base a flattened triangular area 
whose apex extends for nearly 70 mm. toward the tip of the ramus. The termi- 
nal part of the ramus was much broader transversely than in either Paramylodon 
or Mylodon garmani; it was more abruptly truncate, and about 120 mm. across 
as against about 85 in the latter species. It therefore more nearly resembles 
M. robustus in having a broad truncate lower lip, and was thus adapted more for 
a grazing habit, while Paramylodon and M. garmani with their elongate and 
compressed rami, were probably browsing animals. The reduction of the 
humerus in the latter may also be correlated with this habit, implying that it 
raised itself up to reach for branches rather than to grub for roots. The dis- 
tance from the socket of the first tooth to the tip of the ramus in the median 
line is about 150 mm. in both species of Mylodon, but in Paramylodon was 
apparently much greater, since the ramus is more produced in that genus. 
Concerning Paramylodon, as to the validity of which some doubt has 
been expressed, it seems that its claims to generic rank are well founded. Its 
reduced dentition and elongate rostrum, with other characters pointed out by 
Brown seem sufficiently trenchant. The contiguity of the astragalar and tibial 
facets of the fibula, however, cannot be considered of generic value, since this 
condition is also found in M. garmani. 
SUMMARY. 
Of the genus Mylodon, there were at least two types in the North American 
Pleistocene, one represented by M. harlani, a grazing type; the other represented 
by M. garmani, here described, apparently a browsing type. The one had a 
broad lip, heavy humerus, tibial and astragalar facets of the fibula separate; 
the other had a narrower more compressed skull and rostrum, a lighter humerus, 
tibial and astragalar facets not separated (agreeing thus with Paramylodon). 
Also, as a further adaptation to the browsing habit, certain of the dorsal verte- 
brae have three articulating facets for greater mobility in reaching upward, a 
condition found in Megatherium but not in Mylodon robustus, a grazing species 
of South America. 
