The Hamlyn's monkey, also known as the owl-faced monkey, is a species of Old World monkey that inhabits the bamboo and primary rainforests of the Congo. This species is exceedingly rare and known only from a few specimens; little is known about it. However these specimens tend to be widely dispersed throughout the eastern part of Congo, from the Epulu River to the Lukuga River and from the Congo River to the Kabale Forest, with one example in northwestern Rwanda. Geographically it corresponds quite closely to another species of monkey, L'Hoest's monkey C. lhoesti. It travels on the ground, and researchers think that it may be awake primarily by night.