MEGATHERIDA 189 
the feet differ considerably from those obtaining in the type genus. 
S. leptocephalum, the type of the genus, occurs in Patagonia and 
Argentina but 
other species are 
found in Brazil 
and Chili, The 
genus Mylodon, in 
its widest sense, 
may be taken to 
include a number 
of comparatively 
large _Edentates, 
some of which have 
been described 
under the names of 
Grypotherium, Lest- 
odon, and Pseudo- 
lestodon. The teeth 
of the upper jaw 
are generally of an 
oval or subtriangu- 
lar section ; and in 
the more typical forms the first and second teeth are separated 
by a short interval, the ‘former being horizontally worn. In 
other species, however, like Jf. (Lestodon) armatus, there is a 
considerable space between the first and second teeth, and the 
first is worn obliquely. The skull is exceedingly like that of 
the Sloths in general contour; and there is not the descending 
process at the angle of the mandible found in Megatheriwm. 
The humerus has no entepicondylar foramen. The species 
represented in Fig. 63 is from the Pleistocene of South America ; 
but the type of the genus is M. harlam, from beds of corre- 
sponding age in Kentucky. The Patagonian JM. (Grypotherium) 
darwini is a remarkable form, characterised by the presence of a 
bony arch connecting the premaxille with the nasals, of which, as 
already mentioned, there is an {incomplete development in 
Megatherium.  Megalonyz, from the Pleistocene of Kentucky, differs 
from Mylodon by the long interval between the first and second 
teeth, and also by the presence of an entepicondylar foramen in 
the humerus. Nothrotheriwm is a smaller form, occurring in the 
deposits of the Brazilian caves, of which the dental features have 
been already mentioned. The osteological characters of these and 
other allied genera have been fully described in the works of 
Cuvier, Owen, Burmeister, Leidy, Ameghino, Gervais, Reinhardt, 
and others. 
Promegatherium.Two genera from the infra-Pampean beds 
Fic. 63.—Skeleton of Mylodon robustus (Pleistocene, South 
America). From Owen. 
