_Cercocebus_, Geoffr., Ann. Mus., xix., p. 97 (1812).
This genus has been established to receive a small, and but little known,
group of Monkeys, which is confined to West Africa. They are nearly related
to the Macaques on the one side, and even more closely to the genus
_Cercopithecus_, next to be described, on the other side. They all have an
oval head, and in form are more slender than the Macaques; they have also
the muzzle less prolonged, the supra-orbital ridges less developed, the
ischial callosities larger, and the limbs proportionately {37}longer. They
agree with the Macaques, and differ from the _Cercopitheci_, or Guenons, in
having a fifth hinder cusp to the posterior lower molar tooth in each jaw;
and differ from both in the hairs of the body rarely being ringed with
different coloured bars, as is the case with the species of both the genera
just mentioned. The nose is situated behind the end of the muzzle. Their
most obvious external character, however, and one from which they derive
their common name of "White-eyelid" Monkeys, is their pure white upper
eyelids, the white streak being more distinct on the inner half of the
eyelid than on the outer. These Monkeys want the laryngeal air-sacs seen in
the Macaques; but they have large cheek-pouches and a simple stomach, as in
the latter. Their tail is always long, quite equalling the length of the
body. The hands have a web between each of the fingers, that between the
thumb and index finger being very short; in their feet, the great-toe,
which is widespread, has a short web uniting it with its neighbour; the
second and third toes are united nearly throughout their whole length, the
fourth is webbed and united to the third and fifth as far as their
mid-joints.
The Mangabeys are confined to West Africa. Like their relatives, the
Macaques and the Guenons, they are arboreal, living in troops in the forest
country, and feeding chiefly on fruits.