The species of Rhachomyces parasitizing species of the cave-dwelling genera Aphaenops, Geotrechus and Hydraphaenops (Trechini) from the Pyrenees (France and Spain) are studied. Examination of many collections and revision of literature reveal that five species of Rhachomyces are involved. Rhachomyces aphaenopsis is the most common and a fairly variable species, including the synonyms R. dedyi and R. jeannelii. Previous reports of other taxa like R. hypogaeus, R. stipitatus, R. stipitatus var. pallidus and R. maublancii must be removed from the list of Pyrenean parasites of Trechini beetles as they also refer to R. aphaenopsis. The status of R. girardii is validated by addition of a Latin diagnosis. Rhachomyces pyrenaeus, which was only known from the type, was collected again on another host and locality. Additionally, two new species are described: R. ilerdensis on Geotrechus seijasi from Spain and R. spadiceus on Aphaenops spp. from France. The characteristics of extant species are discussed and defined, with special emphasis on R. aphaenopsis. Other taxa are compared when necessary to eliminate the confusion accumulated by old records in the literature. Hosts and localities are also reviewed to offer up-to-date information for all species studied of Rhachomyces occurring in the Pyrenees. © 2007 J. Cramer in der Gebrüder Borntraeger Verlagsbuchhandlung.