There are 13 species of coral-inhabiting megatrematine barnacles of which five or possibly six are extinct. Despite a meager geological record dating from the early Pliocene, it appears, based on their distribution megatrematines are far older than indicated by their fossil record, likely originating early in the Miocene if not the Oligocene. Nonetheless, in apparently maintaining a conservative morphology, especially in their opercular plates, they never attained the diversity of forms such as found in the coral-inhabiting pyrgomatines. However, we propose new taxa herein including Memagreta n. gen. for M. pandorae n. sp., Megatrema youngi n. sp. and Pyrgomina djanae n. sp. The extinct species Pyrgoma elargatum Seguenza and P. sulcatum Philippi are considered valid species and herein assigned to Pyrgomina. Adna Sowerby is reinstituted as a valid genus. The tribe Pyrgominini is proposed for Pyrgomina and Adna and the tribe Megatrematini for Megatrema and Memagreta.