Brachyteles arachnoides, Gray, Cat. Monkeys Brit. Mus., p. 45 (1870).
Characters.—Male.—Size small; face nude, flesh-coloured; general colour of body yellowish-brown, darker on the back of the head, with a few long black hairs on the forehead; hairs of head short and directed backward; buttocks, vent, base of tail and perineal region dark ferruginous-brown; the thumb wanting or rudimentary. Length of body, 22 inches; tail, 26 inches.
Female.—Ashy-brown, instead of yellowish-brown, in appearance.
Young.—In some young specimens the general colour is dark brown, with the sides of the face white.
Dr. Slack observes, in the "Proceedings of the Academy of Natural Sciences of Philadelphia" for 1862, in reference to this species: "I had long suspected that the three species of this genus described by Isidore Geoffroy St. Hilaire, were in reality one and the same; no specific characters are manifest in their coloration, or skulls, the supposed differences being based upon the development of the anterior thumbs, this member being absent in B. arachnoides, replaced by a small nailless tubercle in B. tuberifer, and surmounted by a nail in B. hemidactylus. In the "Magazin" of Messrs. Verreaux, in Paris, I found specimens having upon one hand the tubercle, and upon the other the nailed thumb, others with the tubercle on one hand, but absent upon the other. St. Hilaire himself, in his "Catalogue of the Primates," expresses a doubt as to whether B. arachnoides and B. hemidactylus are really distinct. In September and October, 1860, I was unable to find B. hemidactylus in the Paris Museum, all the Brachyteles being labelled Eriodes arachnoides."
Distribution.—Confined to the wooded region of the south-east of Brazil.
Habits.—Arboreal, diurnal, and (it is supposed) gregarious, frequenting the high forest trees, and subsisting on fruits.
THE SPIDER-MONKEYS. GENUS ATELES.
Ateles, Geoffr., Ann. Mus., vii., p. 262 (1806).
This is the fourth remaining genus of the Cebinæ, the last Sub-family of the Cebidæ. With the description of the Spider-Monkeys, therefore, we shall have passed in review all the species of the New World Platyrrhine section of the Anthropoidea. The species of this group derive their trivial name from their long and slender limbs; the name applied to them, however, in their native forests by the Indians of Brazil is "Coaita." They are characterised by their light and slender body, which is narrower across the loins than across the chest. The head is rounded, the forehead salient, and the muzzle somewhat projecting. Both pairs of limbs are much elongated, the hind-limbs being shorter, however, than the fore-, and the thumb of the fore-limb is sometimes very rudimentary, being only a nailless tubercle—or, in the majority of the species, entirely absent, rendering the hand a much less perfect organ for holding or picking up small objects, such as fruits, &c.; but its absence probably does not affect, if it does not even benefit, the hand as an organ for climbing and catching hold again after a long leap. The nails and other digits of both limbs are compressed, but much less so than in Brachyteles and Lagothrix. The tail is very long, generally exceeding the length of the body and head, and is nude on the under side, and very sensitive towards its termination. As a prehensile organ it has reached the summit of strength and perfection. "It even serves as a fifth hand, as detached objects, otherwise out of reach, can be grasped by it, and brought towards the hand or mouth." (Mivart.) The body is covered with long, rather coarse, generally black, hair, and has no woolly under-fur, as in Lagothrix and Brachyteles.