The term Sloth is commonly applied to all the kinds of animals whose general shape and habits have just been noticed. It is evident, however, that this union of several species under one term is not correct in zoology, and it is necessary to distinguish them by peculiarities which are permanent. A very ready method of distinction is to separate the Sloths into two families, one containing those which have three claws on the fore limbs and the same number on the hind limbs, and the second including those which have only two claws on the fore feet and three on the hinder.
The first family is called the BRADYPODIDÆ, from βραδύς (slow), and πούς (foot), and the second CHOLŒPODIDÆ, from χωλός (halting, lame), and πούς (foot), and both are included in the group TARDIGRADA, or slow-moving Edentata.
The BRADYPODIDÆ include two genera, but many naturalists only acknowledge one. The first is Bradypus. This includes the Sloths with three-clawed fingers on the fore limbs, whose males and females are alike in their fur, and which have the cheek bone (malar bone) with two processes. The upper one is long and dilated at the end, and the lower is long and triangular, and neither of the processes reaches the ear bone. There are in these Sloths, when full grown, five molar teeth on each side in both jaws, and the first is very short. There are two mammæ on the chest.
The second genus is Arctopithecus (Gray), and it contains species which have the males and females dissimilar in their colour and ornamentation, and the malar bone has a thin and narrow upper process.
The second family of the Sloths (the CHOLŒPODIDÆ) contains but one genus, Cholœpus (the Unau), whose species have two claws on the fore limbs and three on the hind ones. The front of the lower jaw is stuck out, and not cut short, and the first molar teeth are long.
The genus Bradypus probably contains several species, but it is only necessary to mention one, which is called
THE COLLARED SLOTH, OR THE HAIRY SLOTH.[58]
This Sloth lives in the densest forests of Brazil, Peru, and Para, and is found not far from Rio Janeiro.
It is a kind of the Three-clawed Sloths, in which there is little or no difference between the fur of the males and females. The neck is surrounded by a large collar of long black hair, and underneath this is a fur of a dark-brown colour. The face is naked, and is of a black colour, and the hair of the body is not very flattened, but is withered-looking to a certain extent. The forehead, temples, chin, throat, and breast are covered with reddish or rust-coloured hair, slightly grizzled. On the crown of the head it is long and yellow, and pale orange on the rest of the body. This Sloth produces one at a birth.