_Sub-family_, Cebinæ.--_Cebus_ (18 sp.), is the largest genus of American monkeys, and ranges from Costa Rica to Paraguay. They are commonly called sapajous. _Lagothrix_ (5 sp.), the woolly monkeys, are rather larger and less active than the preceding; they are confined to the forests of the Upper Amazon Valley, and along the slopes of the Andes to Venezuela and Bolivia. _Ateles_ (14 sp.), the spider monkeys, have very long limbs and tail. They range over the whole area of the family, and occur on the west side of the Equatorial Andes and on the Pacific coast of Guatemala. _Eriodes_ (3 sp.), are somewhat intermediate between the last two genera, and are confined to the eastern parts of Brazil south of the equator. The three last mentioned genera have very powerful prehensile tails, the end being bare beneath; whereas the species of _Cebus_ have the tail { 175}completely covered with hair, although prehensile, and therefore not so perfect a grasping organ.
_Sub-family_, Mycetinæ, consists of but a single genus, _Mycetes_ (10 sp.), the howling monkeys, characterized by having a hollow bony vessel in the throat formed by an enlargement of the hyoid bone, which enables them to produce a wonderful howling noise. They are large, heavy animals, with a powerful and perfect prehensile tail. They range from East Guatemala to Paraguay. (Plate XIV., vol. ii., p. 24.)
_Sub-family_, Pitheciinæ, the sakis, have a non-prehensile bushy tail. _Pithecia_ (7 sp.), has the tail of moderate length; while _Brachiurus_ (5 sp.) has it very short. Both appear to be restricted to the great equatorial forests of South America.
_Sub-family_, Nyctipithecinæ, are small and elegant monkeys, with long, hairy, non-prehensile tails. _Nyctipithecus_ (5 sp.), the night-monkeys or douroucoulis, have large eyes, nocturnal habits, and are somewhat lemurine in their appearance. They range from Nicaragua to the Amazon and eastern Peru. _Saimiris_ or _Chrysothrix_ (3 sp.), the squirrel-monkeys, are beautiful and active little creatures, found in most of the tropical forests from Costa Rica to Brazil and Bolivia. _Callithrix_ (11 sp.), are somewhat intermediate between the last two genera, and are found all over South America from Panama to the southern limits of the great forests.