MAMMALIA. 409 
their feet nearly equal, the anterior possessing four or five fingers, and the 
posterior three or four; the external fingers were deprived of nails. Th» 
tail was very long and powerful. 
The genus Megatherium is characterized by its teeth, which are tetra- 
gonal, and have their crowns transversely furrowed. There are five above 
and four below on each side. The fibula is soldered to the tibia by both 
of its extremities. The fore feet have four fingers, the hind feet only three, 
the two external without nail. Only one species is well known, M. curier’/, 
from South America. In size this exceeded the rhinoceros. Some frag- 
ments of Megatherium have also been found in North America, particularly 
on the coast of Georgia. The Megatherium is supposed to have fed upon 
the leaves of trees, previously uprooted by the animal. 
The genus Megalonyzx is distinguished by its molars, five above and four 
below on each side, sub-elliptical in form, the crown of which is hollowed 
in the middle, whilst the edge remains prominent. The anterior limbs are 
a little longer than the posterior ones, a character which brings them nearer 
the Tardigrada proper than Megatherium. The tibia and fibula are not 
soldered together ; the hind foot is obliquely articulated. The tail is stout 
and robust. The body of Megalonyx was not so heavy as that of the 
Megatherium, but the habits were very likely the same. The first species 
known is M. jeffersonit, of the size of an ox. It was found in a cavern in 
Virginia. A few other species of the same genus have been discovered 
in South America. 
The genus Mylodon had the heavy form of Megatherium, but with a 
quite different dentition. The molars, five above and four below, are worn 
off in plane surfaces. In the upper jaw, the first tooth is sub-elliptical, the 
second elliptical, and the others triangular with the internal surface furrowed. 
In the lower jaw, the first is elliptical, the last but one tetragonal, and the 
last large and bilobated. The form of the head resembles that of Mega- 
therium. The feet are equal, the anterior with five fingers and the posterior 
with four; the two external fingers are deprived of nails, the others provided 
with large phalanges, terminated with semi-conical and unequal nails. 
Species of this genus are found in South America, as far as the pampas of 
Brazil (M. darwinii), and also in North America, in a cave in Kentucky 
(M. harlani). | 
The genus Scelidotherium is nearly allied to Mylodon. The molar teeth 
are five above and four below. The upper ones are all triangular. In the 
lower jaw, the first is triangular too, the second and third a little com- 
pressed, and the fourth large and hilobated. The body heavy and bulky. 
The complete skeleton is not yet known. Four species have already been 
discovered in South America. The largest, S. leptocephalon, was an 
inhabitant of the southern extremity of the continent. The others belong 
to Brazil. 
The genus Platyonyx, with its skull and teeth similar to Bradypus, 
recails to mind the armadiilo, but resembles Megalonyx by its skeleton. 
The character by which it is distinguished from all its congeners consists 
in the high development of its feet. The fore feet, having five depressed 
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