The genus-group taxon Megatrigon Johnson, 1898, stat. nov., is revised and treated as a valid genus within the Merodontini (= Eumerini). Extensive diagnoses are given for the genus and for its three constituent species groups: argenteus group [11 spp.], nivalis group [monotypic], sexfasciatus group [3 spp.]. Five new generic combinations are proposed within Megatrigon: M. argenteus (Walker, 1852) comb. nov., M. flavimarginatus (Hull, 1964) comb. nov., M. jacobi (Hervé-Bazin, 1913) comb. nov., M. nivalis (Hull, 1964) comb. nov. and M. ochreatus (Hull, 1964) comb. nov. All species of the argenteus group are revised and nine new species are described: Megatrigon apiformis sp. nov., M. argentifrons sp. nov., M. argentimaculatus sp. nov., M. cooksoni sp. nov., M. immaculatus sp. nov., M. magnicornis sp. nov., M. natalensis sp. nov., M. sexmaculatus sp. nov., M. tabanoides sp. nov. Within the sexfasciatus group, M. jacobi (Hervé-Bazin, 1913) comb. nov. is treated as a senior synonym of Eumerus connexus Hull, 1964 syn. nov., but no further work is done at the species level due to insufficient material.