This genus is intermediate between the Squirrel-Monkeys and the typical Night-Monkeys. In the Titis, sometimes known by the name also of Whaiapu-Sai Monkeys, the fur is soft, the head small, depressed, and not produced backward as in _Chrysothrix_; the tail is long and bushy; the eyes are small, and the orbits intermediate in size between those of the last and the next genus; the nasal partition is broad, and the ears large. The canine teeth are small, and the angle of the lower jaw expanded, somewhat as in the Howlers (_Mycetes_), though to a less extent. {159}The Titi Monkeys are diurnal animals, arboreal and gregarious, very lively in disposition, noisy and agile, living on fruit, insects, birds' eggs, and even small birds. They range all over South America, from Panama to the southern limits of the forest regions. I. THE WHITE-COLLARED TITI. CALLITHRIX TORQUATA. _Cebus torquatus_, Hoffm., Mag. Ges. Nat. Freund. Berlin, x., p. 86 (1807). _Simia lugens_, Humb., Obs. Zool., i., p. 319 (1811). _Callithrix lugens_, Geoffr., Ann. Mus., xix., p. 113 (1812). _Saguinus vidua_, Lesson, Species Mamm. Bimanes et Quadrum., p. 165 (1840). _Callithrix torquatus_, Geoffr., t. c. p. 114; Gray, Cat. Monkeys Brit. Mus., p. 55 (1870). _Callithrix torquata_, Schleg., Mus. Pays Bas, vii., p. 235 (1876). CHARACTERS.--Head round; face short; ears short, nearly naked; nose flat. Fur soft and woolly, intermixed with many long, stiff, dark reddish-brown hairs,--the hairs red at the base, and black at the tips; forehead black; crown of head dark brown; a narrow band round the face, white; a narrow collar round the neck, reddish-white; hands white; hair of feet red at the base, but black at the tips. Length of the body, about 12 inches. DISTRIBUTION.--Confined to the upper reaches of the Rio Negro, Brazil. HABITS.--This species, often known under the name of the Widow Monkey, is said to be very gentle in disposition. {160}When approaching to capture insects or small birds, which form its prey, it becomes keen and excited, but at other times it appears to be dull and listless. They roam about in flocks of about half a dozen individuals, on the large branches of the great forest trees. They are noisy animals, and in the early morning they make the forest resound with their yelping cries. II. THE RED TITI. CALLITHRIX CUPREA. _Callithrix cuprea_, Spix, Sim. et Vesper. Bras., p. 23, pl. 17, (1823); Gray, Cat. Monkeys Brit. Mus., p. 54 (1870); Schleg., Mus. Pays Bas, vii., p. 236 (1876); Thomas, P. Z. S., 1880, p. 394. _Callithrix discolor_, Is. Geoffr., C.R., xxvii., p. 498 (1848); id. Cat. Méth. Primates, p. 41 (1851); id. Arch. Mus., v., p. 551, pl. 28; Wagner in Schreb., Säugeth. Suppl., v., p. 114 (1855). (_Plate XIV._)