This is the fourth remaining genus of the _Cebinæ_, the last Sub-family of the _Cebidæ_. With the description of the Spider-Monkeys, therefore, we shall have passed in review all the species of the New World Platyrrhine section of the _Anthropoidea_. The species of this group derive their trivial name from their long and slender limbs; the name applied to them, however, in their native forests by the Indians of Brazil is "Coaita." They are characterised by their light and slender body, which is narrower across the loins than across the chest. The head is rounded, the forehead salient, and the muzzle somewhat projecting. Both pairs of limbs are much elongated, the {228}hind-limbs being shorter, however, than the fore-, and the thumb of the fore-limb is sometimes very rudimentary, being only a nailless tubercle--or, in the majority of the species, entirely absent, rendering the hand a much less perfect organ for holding or picking up small objects, such as fruits, &c.; but its absence probably does not affect, if it does not even benefit, the hand as an organ for climbing and catching hold again after a long leap. The nails and other digits of both limbs are compressed, but much less so than in _Brachyteles_ and _Lagothrix_. The tail is very long, generally exceeding the length of the body and head, and is nude on the under side, and very sensitive towards its termination. As a prehensile organ it has reached the summit of strength and perfection. "It even serves as a fifth hand, as detached objects, otherwise out of reach, can be grasped by it, and brought towards the hand or mouth." (_Mivart._) The body is covered with long, rather coarse, generally black, hair, and has no woolly under-fur, as in _Lagothrix_ and _Brachyteles_.