The genus Nopoiulus is revised. Four species are recognized: minutus (Brandt, 1841), kochii (Gervais, 1847), breuili Brölemann, 1921, and anatolicus Lohmander, 1939. A key to the species is presented, and the gonopods and vulvae of minutus are described for the first time. This species is remarkable for its apparent parthenogenesis (males extremely rare) and for possibly being endemic to North America. The nomenclature of kochii is discussed. A lectotype is designated for Blaniulus venustus Meinert, 1868.