Schwarz (1928) grouped this species with C. l'hoesti, while Elliot (1913) noted its distinctive cusp pattern on the third molar, and reassigned it to a separate genus, Rhinostigma.

[5] Some published reports indicated that Hamlyn's monkey lives in small groups, of ten members or less, with one male and multiple females, with no data to show them occurring in monogamous groups.

[7] In color it is generally dark gray, with a characteristic white stripe which extends from the root of the nose to the upper lip, giving it an owl-like appearance, hence the name "owl-faced monkey".

The name "Hamlyn's monkey" and the scientific epithet "hamlyni" come from the animal dealer who first brought this species to the London Zoo.

[4] Like others of this genus, it covers a wide area in its daily travels, mostly in a search for food.