ABSTRACTA new family, Sigmoideomycetaceae, is proposed forSigmoideomyces, Thamnocephalis, and a new genusReticulocephalis.The family is characterized by sporophores having fertile heads composed of dichotomously branched, coiled hyphae in which the width of the coil is largest distally. Usually, each branch terminates in a sterile spine, which can either be free or adherent to other spines; modified spines may bear hyphal coils. All fruiting hyphae, including spines or modified spines, are irregularly septate at maturity. Cells formed at each branching point of a sporangiophore, except the final one or two, bear a pair of stalked fertile vesicles covered with pedicellate, unispored sporangiola.Reticulocephalis, Sigmoideomyces, andThamnocephalishave similarly constructed fertile heads but differ in the habit of the sporophore. InThamnocephalisthe fruiting structure is stalked and the fertile head is elevated well above the substratum, whereas inReticulocephalisandSigmoideomycesthe fruiting structure is sessile or procumbent. InReticulocephalisthe sterile spines have adherent tips and the sporangiola are smooth walled, whereas inSigmoideomycesthe sterile spines are free and the sporangiola have finely echinulate walls. Two new species are described:Reticulocephalis gyrosus, which produces coils of hyphae on the apices of modified sterile spines, andThamnocephalis sphaerosporawhich forms smooth-walled to faintly spinose sporangiola and spherical to obovoid fertile vesicles.Sigmoideomyces divaricatusis emended to indicate that the sterile spines are nearly evanescent, leaving behind only a wispy remnant of the wall, which is not due to filamentous bacteria as suggested by the original author. Sigmoideomycetaceae are hypothesized to be monophyletic.Reticulocephalis, Sigmoideomyces, andThamnocephalis, and all of their species, are monophyletic. All three genera are patristically equidistant from the hypothetical ancestor. OnlyCunninghamellais retained in Cunninghamellaceae. Keys to the genera and species are provided. A revised family description is presented for Cunninghamellaceae.