ABSTRACTA fourth species of the Australasian genusAustrosmittium, A. biforme(Trichomycetes, Harpellales), has been found. This gut fungus from Chironomidae larvae collected in a Tasmanian stream has the unusual feature of producing two distinctly different sizes of trichospores. Two new Tasmanian species of the more common genusSmittium, S. compactumandS. fastigatum, are described from lotic chironomid larvae. A new species of Harpellales from Tasmanian mayfly nymphs is also described and illustrated, but not named; it may represent a new genus that has similarities toBojamyces repensrecently described from the USA. New records of other Tasmanian trichomycetes from aquatic insects are provided.