Hamlyn's monkey
Also known as an owl-faced monkey, it inhabits the bamboo and primary forests of the Congo basin. It is incredibly rare, and only known from a few specimens (it should be noted, that while we know relatively little about it in the wild, they are kept in a few zooalogical collections around the world). Despite this, they appear to inhabit a huge area, covering 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.
This range matches to another species of monkey quite well – L’Hoest’s monkey C. lhoesti. It travels on the ground, and researchers think that it may be awake primarily by night.