ABSTRACTEjectosporus magnusbelongs to a new monotypic genus of Harpellales (Trichomycetes) found in the hindgut ofAllocapniaspp. nymphs (Plecoptera, Capniidae). The mature sporangiospore is forcefully ejected from the trichospore, a monosporous sporangium, while the sporangial wall remains attached to the generative cell. Trichospores apparently do not break away from the thallus as in most other genera of Harpellales. No trichospore appendages were observed. Another new hindgut species fromAllocapniaspp. nymphs,Paramoebidium corpulentum(Amoebidiales), is also described. The first axenic isolations ofSimuliomyces spica(Harpellales) from these stonefly hosts are reported.