of his most skilful Indians, who were absent hunting for three weeks before they obtained twelve specimens. [Illustration: Fig. 8. Map of part of the basin of the Amazons to show the distribution of the Uakarí Monkeys. (Forbes, P. Z. S., 1880, p. 647.) Supposed area of ''B. melanocephalus'', ''B. calvus'', and ''B. rubicundus'' shown by shading.] In reference to the singularly restricted range of these Uakarís, Mr. Wallace's observations in his paper "On the Monkeys of the Amazon," before the Zoological Society of London, are of great interest. "During my residence," he says, "in the Amazon district, I took every opportunity of determining the limits of species, and I soon found that the Amazon, the Rio Negro, and the Madeira formed the limits beyond which certain species never passed. The native hunters are perfectly acquainted with this fact, and always cross over the river when they want to procure particular animals, which are found even on the river's bank on one side, but never by any chance on the other. On approaching the sources of the rivers, they cease to be a boundary, and most of the species are found on both sides of them. Thus several Guiana species come up to the Rio Negro and Amazon, but do not pass them; Brazilian species, on the contrary, reach but do not pass the Amazon to the north. Several Ecuador species from the east of the Andes reach down into the tongue of land between the Rio Negro and Upper Amazon, but pass neither of those rivers, and others from Peru are bounded on the north by the Upper Amazon, and on the east by the Madeira. Thus there are four districts whose boundaries on one side are determined by the rivers I have mentioned. In going up the Rio Negro, the difference on the two sides of the river is very remarkable. {182}"In the lower part of the river you will find on the north the _Jacchus_ [_Hapale_] _bicolor_, and the _Brachyurus couxui_ [_Pithecia satanas_], and on the south the red-whiskered Pithecia. Higher up you will find on the north the _Ateles paniscus_, and on the south a black _Jacchus_ and the _Lagothrix humboldtii_." THE SAKIS. GENUS PITHECIA. _Pithecia_, Geoffr., Ann. Mus., xix., p. 115 (1812). _Chiropotes_, Gray, Cat. Monkeys Brit. Mus., p. 60 (1870), in part. The Sakis form the second section of the present Sub-family, and are characterised by their long, thick, and bushy non-prehensile tail. A thick beard conceals the large chin. Hair on the crown long, divided by a central line, and hanging over the head, half concealing the pleasing diminutive face, or confined to the head, cheeks, and chin. The ears are large. The upper and lower incisor teeth project forward, the upper inner pair being moderately large, the outer very small; canines strong and conical; first pre-molar smaller than the others, and one-cusped; molars with square crowns, grooved in the middle and slightly four-cusped.