MEGATHERIUD.E 183 
unlike the true canines of heterodont mammals. Vertebre: C 6 
or 7, D23-24, L3, 87-8, C 4-6. One species (C. didactylus) has 
the ordinary number of vertebra in the neck; but an otherwise 
closely allied form (C. hoffmanni) has but six. The tail is very 
rudimentary. The hand generally resembles that of Bradypus ; but 
there are only two functional digits with claws—those answering 
to the second and third of the typical pentadactylate manus. The 
structure of the hind limb generally resembles that of Bradypus, 
the appellation “two-toed” referring only to the anterior limb, 
for in the foot the 
three middle toes 
are functionally 
developed and of 
nearly equal size. 
C. didactylus, which 
has been longest 
known, is com- 
monly called by 
the native name 
of Unau. It in- 
habits the forests 
of Brazil. C. hoff- 
mann (Fig. 58) 
has a more north- 
ern geographical Fic. 59.—Skull Of Bwo-toed Sloth (Cholospus didactylus). From 
< Proc. Zool. Soc. 1871, p. 432. 
range, extending 
from Ecuador through Panama to Costa Rica. Its voice, which 
is seldom heard, is like the bleat of a sheep, and if the animal is 
seized it snorts violently. Both species are very variable in 
external coloration. 
Nothropus.1—The only fossil form which has been referred to 
this family is indicated by a lower jaw, described by Dr. Burmeister, 
from the Pleistocene of Argentina, which appears to have belonged 
to an animal of about double the dimensions of Cholapus didactylus. 
Professor Cope states, however, that this jaw really belongs to a 
Glyptodont; while it is referred by Dr. Ameghino to the next 
family. 
Family MEGATHERIID-£. 
The members of this family are all extinet. Their characters, 
so far as is known from the well-preserved remains of many species 
found abundantly in deposits of Pleistocene age in both North and 
South America, were intermediate between those of the existing 
Bradypodide and the Myrmecophagide, combining the head and 
1 Burmeister, Sitzb. lk. Berlin, vol. xxviii, p. 613 (1882). 
