SUMMARYA new genus and species of corticolous Myxomycetes,Trabrooksia applattata, is characterized by its flattened plasmodiocarps and depressed sporangia, glossy to iridescent peridium, limeless fructifications, subparallel arrangement of the hyaline, mostly unbranched capillitial threads, and the dark color of the spores. It is tentatively placed in the Didymiaceae but with further study may require a separate family. An updated key to the genera of the Didymiaceae is provided to aid in the identification of this taxon.