Trichomycterus belensis, new species, is described from a tributary to Laguna Blanca, a high-elevation drainage in the Departamento Belén, Provincia de Catamarca, Argentina. The new species is distinguished from other members of the apparently nonmonophyletic genus Trichomycterus by a combination of features involving the premaxilla, dentition, barbel form, pigmentation, and morphometrics. Trichomycterus alterus, whose original description was based on a limited number of specimens, is redescribed based on numerous specimens from localities in the central and northwestern portions of Argentina.