A systematic revision of the Cainozoic Trigoniidae (Mollusca:Bivalvia) reveals that the family is represented by two genera: Eotrigonia (Paleocene-Late Miocene), known only from southern Australia with species E. paleocenica sp. nov., E. eocenica sp. nov., E. tubulifera (Tate), E. intersitans (Tate) and E. subundulata (Jenkins) (= semiundulata Jenkins, = granosa Pritchard = lutosa Pritchard); and Neotrigonia (Middle Miocene-Recent) with fossil species N. acuticostata (McCoy) (= trua Cotton), N. howitti (McCoy), N. medipontea sp. nov., N. strangei (A. Adams), N. margaritacea (Lamarck) and N. uniophora (Gray), of which the latter three are found living. N. novaguineana Skwarko occurs in the Neogene of New Guinea. Both genera are placed in the Trigoniinae. Eotrigonia evolved from Trigonia s.s. in the latest Cretaceous or earliest Tertiary and Neotrigonia from Eotrigonia in the Oligocene or early Miocene. A neotype is designated for E. subundulata Jenkins. Trigonia miriana Skwarko, a possible ancestor of the Tertiary representatives, is redescribed.
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