The morphology of several “low-mantle” species of Aulacoseira found in Western North America is studied. A new taxon, Aulacoseira pardata sp. nov., is described. Aulacoseira pardata is similar to Aulacoseira distans and Aulacoseira lirata and has been confused in the past with these two taxa. Aulacoseira distans var. nivalis and Aulacoseira distans var. nivaloides bear significant morphological differences from Aulacoseira distans. These two varieties are therefore elevated to species status: Aulacoseira nivalis comb. nov. and Aulacoseira nivaloides comb. et stat. nov., respectively.

New taxa: Aulacoseira pardata English and Potapova

New combinations: Aulacoseira nivalis, Aulacoseira nivaloides.