Professor Weldon writes, in his paper in the "Proceedings of the Zoological Society," referred to above: "Sir W. Flower has suggested to me that the enormous depth of the _ramus_ of the mandibles in this _Callithrix_ pointed to the existence of some arrangement resembling that of _Mycetes_. It was difficult to determine this point in a young female; but the swollen condition of the thyroid, together with the existence of a patch of ossification on each side, seem to show the possible existence of a howling apparatus in the male." THE DOUROUCOLIS. GENUS NYCTIPITHECUS. _Nyctipithecus_, Spix, Sim. et Vespert. Bras., p. 24 (1823). The members of this genus, usually called "Douroucolis," are small animals, somewhat Lemurine in appearance, possessing a short, thick body, a rounded head produced behind, and a short, round face, encircled by a ruff of whitish fur. The muzzle is not prominent; the mouth and chin are small; the {167}ears are very short, scarcely appearing above the hair of the head; the eyes are enormous and yellowish in colour, imparting to them the staring expression of nocturnal animals of prey. Their tail is bushy, moderately long and non-prehensile; and the nostrils are separated by a narrower partition than in the other genera of the sub-family. Their physiognomy reminds one of an Owl or Tiger-cat (_Bates_). They are covered with close, soft, woolly fur. In the skull the orbits are enormously large and closely approximated, but yet separated by a complete bony wall; the nostrils, on the other hand, though separated in the living animal by a wide, fleshy partition, have only a thin plate of bone between them. The upper incisors are broad; the canines long; and the lower incisors project forwards, somewhat as in the Lemurs. The arm-bone has a perforation (the ent-epicondylar foramen) on its inner side above the articulation of the elbow joint, to give passage and protection to an important artery and nerve. The thumb is very short; the claws are small and weak. The dorsal and lumbar vertebræ together number twenty-two, the greatest number possessed by any American monkey. As in _Chrysothrix_, the external surface of the cerebral hemispheres is smooth and almost devoid of convolutions, but their inner faces exhibit several of the more important grooves seen in the higher Apes. All the species are arboreal and nocturnal, hiding away in the daytime and roaming during the night, giving vent to loud howls, or Cat-like cries, as they move in quest of the insects, small birds, and fruits, which form their food. They range from Nicaragua to the Amazon and Eastern Peru, and are called "Devil monkeys" by the Indians. They are very delicate, and soon die in captivity. {168}I. THE THREE-BANDED DOUROUCOLI. NYCTIPITHECUS TRIVIRGATUS. _Aotus trivirgatus_, Humboldt, Obs. Zool., p. 306, fig. 28 (1811).