As stated in Brinkhurst and Wetzel (1984, p. 50), 'The recent history of this genus is complex, and it is simpler to refer the reader to the recent literature than to attempt to review all the activity in detail. The major debate revolves around the type species [Peloscolex variegatus Leidy, 1851], a taxon described very briefly by Leidy (1851)...' MJW encourages those interested in the complex history of this genus, and the species assigned to it since 1851, are referred to further information presented in Brinkhurst (1962), Holmquist (1978, 1979), Brinkhurst (1981), Brinkhurst and Wetzel (1984), literature cited in these publications, all discussions and references to generic and species descriptions therein, and species reassigned to and those subsequently described in the genera Spirosperma Eisen, 1879, Quistadrilus Brinkhurst, 1982, Baikalodrilus Holmquist, 1978, Haber Holmquist, 1978, Tubificoides Lastockin, 1937, and Tasserkidrilus Holmquist, 1985 as a starting point for understanding this genus' history; there are no valid species in this genus known to occur in North America, and I believe that all taxa formerly aligned with this genus have been reassigned to or synonymized with other taxa