In this study, we review the taxonomy of Saguinus niger (É. Geoffroy) and revalidate Saguinus ursula Hoffmannsegg as a distinct species. The revalidation is based on pelage coloration, and the pattern of morphological divergence is corroborated by molecular data. Samples from the east bank of the Tocantins River (S. ursulus) were distinct from specimens of S. niger from the west bank in having mid-dorsal hair with an wide (5.0-55 mm) intermediary band of bright and golden buffy color; long (ca. 23-26 mm) dorsal hair at the inter-scapular region; and naked (not noticeably haired) face, hands and fingers. Saguinus ursulus and S. niger are allopatric, and Tocantins River is putatively acting as an effective barrier for gene flow. A lectotype to S. ursulus from syntypes was designated.