Trichomycterus pseudosilvinichthys, new species, is described from midelevation drainages in the Provincia de La Rioja, Argentina. The new species is distinguished from other members of the apparently nonmonophyletic genus Trichomycterus by having the insertion of the first proximal dorsal-fin pterygiophore at, or posterior to, vertebra 20 to 22; the presence of the pelvic fin and girdle; a fronto-lachrymal tendon bone with a lateral expansion but an incomplete laterosensory canal segment; the absence of a portion of the supraorbital laterosensory canal running between the frontal and nasal bones with the resultant loss of pore 3; the possession of 17–19 ribs; a first pectoral-fin ray that is not prolonged as a short filament; and the tip of the pelvic fin falling short of the anus.