The new crustose lichen genus Tasmidella, containing the species, T. variabilis sp. nov. with two varieties, var. variabilis and var. inactiva var. nov., is described. Tasmidella is most closely related to Megalaria, from which it differs chiefly by having simple ascospores with a layered wall. Relationships with superficially similar genera are discussed. A revised circumscription of the family Megalariaceae is provided to take into account the inclusion of a second genus.