During the 1992 and 1993 field seasons, several new specimens of Branisella boliviana, the oldest fossil platyrrhine, were discovered in the late Oligocene deposits at Salla, northwestern Bolivia. The new materials are two maxillary fragments and seven mandibular fragments, including P3 and P2, neither of which have previously been recovered. All new and previously reported materials, including the holotype and referred specimens, were apparently recovered from the same horizon, called the Branisella zone (MacFadden et al. [1985] J. Geol. 93:223-250; MacFadden [1990] J. Hum. Evol. 19:7-21. The crown morphology of the newly discovered upper and lower premolars suggests that Branisella has a close affinity with callitrichines. A detailed examination of all molar specimens suggests that "Szalatavus attricuspis," which was recovered at Salla in 1981 and described as a new genus by Rosenberger et al. (1991), is a junior synonym of Branisella. The Branisella-like upper molar, in which a small hypocone is preserved on the poorly developed distolingual cingulum, is a shared-derived character with callitrichines and does not correspond to the primitive state for platyrrhine phylogeny. The ancestral upper molar morphotype for platyrrhines should have a moderate to large hypocone and a well developed talon area.