A new species of Steindachnerina, family Curimatidae, is described from the headwaters of the Rio Jamanxim in the central portion of the Rio Tapajós basin of the Brazilian Amazon. The species is distinguished from its congeners on the basis of pigmentation and various meristic and morphometric features. The phylogenetic placement of the new species within Steindachnerina is investigated, and notwithstanding the similarities in pigmentation patterns between that species and S. fasciata, those forms were not found to be closely related. The new species represents the first reported occurrence of a species of Steindachnerina within the Rio Tapajós, the fifth largest component of the Amazon. The occurrence of a second species of the genus, S. fasciata, in the Rio Teles Pires, another tributary of the Rio Tapajós basin is also documented. Steindachnerina brevipinna, a species widespread through major portions of the Río de La Plata system, is confirmed to occur in the Rio Xingu of the Amazon basin.