A revision of the genera of the Desmoscolecida is given, based on a reappraisal of key characters. A tentative cladogram is proposed in attempt to establish a theory of relationships within the Desmoscolecida. A new species Desmoscolex (Protricomoides) pravus sp. nov. is described and additional information or a redescription is given of D. (P.) squamosus (Timm), Tricoma (Quadricoma) cobbi (Steiner), T. demanema nov. nom., T. (D.) deuterum (Timm) and Protricoma squamosa Timm, 1970.