PROC. BIOL. SOC. WASH. 94(4), 1981, pp. 1048-1067 A CONTRIBUTION TO THE TAXONOMY OF THE TUBIFICINAE (OLIGOCHAETA: TUBIFICIDAE) Ralph O. Brinkhurst Abstract. — The former genera Isochaeta and Peloscolex are revised. Both names are rejected on the basis of inadequate description of the orig-inal type-species. Isochaetides is modified to include 8 species, all with bifid setae. Varichaeta, new genus, consists of 2 former Isochaeta species plus V. pacifica, new species, all with hair and pectinate setae and distinctive male ducts. Peloscolex now contains 8 unidentifiable taxa, the other species in the genus being attributed to Tubificoides (marine species), Spirosperma (8 species), Baikalodrilus (4 species), Haber (possibly as many as 9 species), and Quistadrilus, new genus, for Peloscolex sensu Holmquist, with 1 species. Introduction Investigation of specimens from Mowich Lake, Mount Rainier, Washing-ton collected by G. Larson in 1966 led to the tentative identification of Isochaeta nevadana and a species said to resemble both Peloscolex var-iegatus Leidy and P. nikolskyi Last, and Sol. (Brinkhurst 1979). Recent collections of large numbers of these enables them to be redescribed, but the nomenclature cannot be settled without a revision of both Isochaeta and Peloscolex sensu Brinkhurst (1971). In the course of this study other relevant material collected by Mr. M. Barbour, J. Hiltunen, K. Stimpson, and Dr. M. Loden was brought to my attention, and examination of them has added to this manuscript. Full bibliographic citations to all species named will be found in Brink-hurst (1971) if not cited in the text. Isochaeta Pointner, 1911 Type-species. — Isochaeta virulenta Pointner, 1911. The type-material of /. virulenta was traced to the University of Graz by Brinkhurst (1963), but despite subsequent work on the River Danube (in which it was first found) and other extensive studies in central Europe, the species has not been rediscovered. Hrabe (1966) reexamined the type and declared it to represent partially mature specimens of Limnodrilus udeke-mianus Clap. 1862. There is sufficient doubt about the existence of the species that it seems best to regard it as species dubium.