Small larvae, up to 4 mm long.
Antenna with 6 segments; segment 3 shorter than segment 4, segment 6 vestigial and hair-like. Blade about as long as flagellum. Lauterborn organs large, longer than antennal segment 3.
Labrum with SI modestly branched, with stronger apical tooth or paired teeth and 4-6 lateral branches each side; other S setae simple. Weakly sclerotized labral lamellae present between SI. Pecten epipharyngis consisting of 3 simple, very short spines. Chaetulae laterales simple; chaetulae basales weakly notched apically. Premandible with 2 teeth; brush absent.
Mandible with apical tooth shorter than combined width of 3 inner teeth. Seta interna slender, consisting of 5 branches, plumose on inner side.
Mentum with two median teeth and 5 pairs of lateral teeth present; 2 outer pairs small. Ventromental plates distinct, with indication of second pair of plates inside main plates; beard absent.
Maxilla with pecten galearis present. Anterior lacinial chaeta apparently shorter and broader than other lacinial chaetae.
Body with no distinct body setae. Procercus longer than wide, relatively small, with 6 moderately long anal setae. Anal tubules about as long as or slightly shorter than posterior parapods.
Larval Psilometriocnemus live in damp soils around springs and seeps near first order streams.
The genus appears restricted to the western Nearctic region.