Graells's tamarin, Saguinus graellsi, is a species of tamarin from the northwestern Amazon in southeastern Colombia, eastern Ecuador and northeastern Peru. It has often been treated as a subspecies of the Black-mantled Tamarin, but differs from that species in having a dull olive-brown (no reddish-orange) lower back, rump and thighs. The two are often said to be sympatric in Colombia (a major argument for treating them as separate species), though the accuracy of such reports has been questioned.
Rylands AB and Mittermeier RA (2009). "The Diversity of the New World Primates (Platyrrhini)". In Garber PA, Estrada A, Bicca-Marques JC, Heymann EW, Strier KB. South American Primates: Comparative Perspectives in the Study of Behavior, Ecology, and Conservation. Springer. pp. 23–54. ISBN978-0-387-78704-6.