Skull longer and less vaulted; brain-case proportionately more compressed from side to side; the muzzle longer, and the orbit smaller, than in _Avahis_; floor of orbit higher than the bony margin of the jaw; inter-orbital space flat; nasal bones, though long, not extending in front as far as the end of the pre-maxillary bone; mandible elongated, narrower, and less deep than in _Avahis_. Bony palate short, posterior margin thickened, and with a foramen behind the posterior molar; line of union of the two halves of the lower jaw shorter than in _Avahis_; its angle very large. No central bone in the wrist (or _carpus_); hind-limb (with or without the foot), compared with the fore-limb (with or without the hand), longer than in any other of the Primates, except _Galago_. _Upper teeth_: Incisors, sub-equal, set close together and subject to variation in size; canine, vertically taller than, and not separated by a gap from, the pre-molar; pre-molars compressed, and having an inner cusp; anterior molars, four-cusped, with the supplementary cusps weak, and with no oblique ridge; anterior and median, with their outer and inner cusps opposite; posterior molar, which is the smallest grinder of the jaw--four-cusped, with transverse, but no oblique ridges. _Lower teeth_: Incisors, with marked longitudinal ridges to the outside (peculiar to this genus); pre-molars sub-equal; molars all four-cusped, and the posterior ones expanded behind. Brain highly organised. A large laryngeal pouch (present {107}also in the foetus), but differing from that of the Apes, is placed between the gullet and windpipe, communicating with the latter by an orifice: main arteries of the fore- and hind-limbs not broken up into a _rete mirabile_ of small parallel vessels, as in many species of Lemurs. Face naked, sometimes blackish, generally dark grey; lips downy; head, neck, back, shoulders, arms, and hands, deep black; fore-arms faintly washed with rufous; a large patch, widening from the middle of the back downwards to the lower back, rump, and root of the tail pure white, washed with orange or red; a patch on each flank, pale, becoming rufous or greyish-white, separated from the rump-spot by black bands continuing down the outer side of the inner face of the thighs, and the front and inner sides of the legs; thighs ashy-grey, their upper two-thirds greyish, becoming black on the front, and ashy-grey on the hinder surface, of the leg. Feet black; tail stumpy, fawn-colour, brownish-grey at the tip; under side rusty brown; abdomen grey; heel rufous. Many varieties of this species have been met with. Of these, some have the top of the head and between the eyes greyish-white, mixed here and there with black; jaws and throat, grey; ears, neck, back and upper part of arms, black; the fore-arms grey; the hands black; a patch on the lower back ashy-grey; flanks bright rufous; legs grey; band on front of the thighs black; heel bright rufous.