Subgenus Xystonotus Wolcott, 1900

Diagnosis: Swimming setae absent; posterior suture lines of Cx-IV extending posterolaterally and not surrounding the genital field.

Distribution: Holarctic. 13 species (some still undescribed) known from North America and an additional species collected at a high elevation (3200 m) in Mexico State, Mexico (Cook 1976, 1980). One species widespread in Western, Central and Southern Europe and one species from South Iran (Asadi and Pešić 2010).