Taxonomic combinations have been made involving the two genera Idiasta Foerster and Rhacalysia Cameron. Four new species are described from Brazil: Idiasta rupina sp. nov., Rhacalysia ampla sp. nov., Rhacalysia jatai sp. nov., and Rhacalysia monteiroi sp. nov. Dichotomous identification keys to the Neotropical species of Idiasta and Rhacalysia are provided. Phaenocarpa delicata Papp, 1969 is included in Rhacalysia and is a new combination.