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 traversed by the Rio Negro; the Bald-headed Ouakari appears to be confined to the triangle formed by the union of the Amazon with another affluent, the Japura; and the Red Ouakari to the forests on the north bank of the Amazon opposite Olivença, and lying between the main stream and the River Iça. Each of them evidently takes the place of the others in its particular district. Of this peculiar kind of distribution few instances are known amongst mammals, but many somewhat similar cases have been observed in birds, reptiles, and insects."

The genus Pithecia, the Sakis, consists of five species with long bushy tails, which are non-prehensile. They are bearded and have a thumb. Like the last genus, Pithecia does not extend into Central America. The incisors project forwards, and the lower jaw is deep, though the howling apparatus of Mycetes is wanting. The thin, closely-set, and projecting incisors are very suggestive of those of the Lemurs. Brachyurus is much like Pithecia in this respect, and both differ markedly from such a genus as Cebus, where the lower incisors are vertical. An anatomical peculiarity of Pithecia is the breadth of the ribs. P. satanas is perhaps the best-known species, but all five have been exhibited at the Zoological Society's Gardens. As its name suggests, P. satanas is entirely black; it shows a curious point of difference from P. cheiropotes in its way of drinking. The latter species, as its name denotes, uses its hand to drink, while P. satanas puts its mouth to the water. P. albinasa is black with a red patch on the nose, within which again is a small white patch.

The Catarrhine Apes are divisible into three or perhaps only two families, the Cercopithecidae and the Simiidae, to which must be added the Hominidae. The Simiidae are sometimes spoken of as the Anthropoid Apes.

'''Fam. 1. Cercopithecidae.'''—Of the Cercopithecidae there are eight genera (perhaps nine) to be recognised, which may be distributed into two sub-families. The first of these two sub-families, that of the Cercopithecinae, has the following characters:—There are cheek pouches in which the animals store food temporarily.