Four genera—Archaeoscelio Brues; Cobaloscelio Johnson and Masner, new genus; Plaumannion Masner and Johnson, new genus; and Huddlestonium Polaszek and Johnson, new genus—lack laterotergites and laterosternites in the metasoma, one of the synapomorphies of the superfamily Platygastroidea. The Baltic amber species Archaeoscelio rugosus Brues and Archaeoscelio filicornis Brues are diagnosed and figured, and two species from Baltic amber are described in Cobaloscelio—C. cuspidatus Johnson and Masner, new species and C. speculifer Johnson and Masner, new species. Plaumannion fritzi Masner and Johnson, new species Brazil and Plaumannion yepezi García, new species Venezuela are described. Huddlestonium exu Polaszek and Johnson, new species is described from São Tomé and the Ivory Coast. The wing venation of Scelionidae is reinterpreted, and the marginal vein of Scelionidae and Chalcidoidea is considered to be a convergent feature.