Cruz Lima's saddle-back tamarin Saguinus fuscicollis cruzlimai Hershkovitz, 1966, was described from a painting by Eládio da Cruz Lima in his book Mammals of Amazonia, Vol. 1, Primates (1945). The painting was of four saddle-back tamarins from the upper Rio Purus, one of them distinct and the inspiration for Hershkovitz to describe it as a new subspecies. Its exact provenance was unknown, however, and the specimen was lost. Surveys in the Purus National Forest in 2011 resulted in sightings of this tamarin along the north bank of the Rio Inauini, a left-bank tributary of the middle Purus, and also on the left bank of the Purus, north and south of the Rio Inauini. It is possible that it extends north as far as the Rio Pauini, and that S. f. primitivus Hershkovitz, 1977, occurs north of the Pauini as far the Rio Tapauá, both also left-bank tributaries of the Purus. Morphometric and molecular genetic analyses and the coloration of the pelage indicate that this tamarin differs from its neighbors sufficiently to be considered a full species. In his doctoral dissertation [2010, Taxonomy, Phylogeny and Distribution of Tamarins (Genus Saguinus Hoffmannsegg, 1807) Georg-August Universität, Göttingen], C. Matauschek found that saddle-back and black-mantle tamarins diverged from the tamarin lineage around 9.2 million years ago; time enough to warrant their classification in a distinct genus. Leontocebus Wagner, 1840, is the first name available. In this article we re-describe Cruz Lima's saddle-back tamarin. We propose a neotype with a precise locality, and make it a full species in the genus Leontocebus.