The diverse fauna from Salla, western Bolivia, represents a rare glimpse into the evolutionary history of Tertiary South American mammals outside of Patagonia (Argentina). The Hegetotheriidae (Notoungulata) from the Deseadan of Salla are composed of two taxa, a new genus and species and a species of Prohegetotherium. Sallatherium altiplanense gen. et sp. nov., differs from Prohegetotherium by its very long, thin nasals; more medially placed labial groove on upper cheek teeth; more reduced I2-I3-C and i3-c separated by diastemata; and much narrower symphysis. The smaller, more common hegetothere from Salla is identified as Prohegetotherium schiaffinoi; the abundant new material from Bolivia permits a better characterization of this otherwise poorly known species from Uruguay and Argentina (Corrientes and Entre Ríos provinces). The Divisaderan Ethegotherium carettei from Argentina is regarded as a junior synonym of P. schiaffinoi, extending the chronologic range of the genus into the early Oligocene. A revised diagnosis of the type species of Prohegetotherium, P. sculptum, is provided based on new material. This species is known exclusively from Argentina.