A systematic revision of the genera Georthocladius Strenzke, 1941 and Parachaetocladius Wülker, 1959, and a key to adult males is presented. Two new Holarctic species are diagnosed and described based on morphological characters of the adult male: Parachaetocladius pyrenaeus sp. n. (Palaearctic region) and Parachaetocladius broankerothurrie sp. n. (Nearctic region). Additional taxonomic notes on related genera of Orthocladiinae and synonymies for four species from Japan are also provided, which include: Parachaetocladius kuramasingularis (Sasa, 1989), Parachaetocladius kamiovatus (Sasa & Hirabayashi, 1993), and Parachaetocladius sunabaabeus (Tanaka & Sasa, 2001) being the junior synonyms of Parachaetocladius akanoctavus Sasa & Kamimura, 1987. An updated checklist of both Georthocladius and Parachaetocladius species with taxonomic remarks, ecology, discussions and a provisional key for adult male are also provided.
