Here, based on phylogenetic analyses of 18 taxa and 57 morphological characters, we propose a new firefly genus,Costalampysgen. nov., to accommodate eleven species. Five new species are herein described:C. bellasp. nov.,C. capixabasp. nov.,C delicatasp. nov.(designated as type species),C. joanaesp. nov.andC. minimasp. nov.In addition, six species are redescribed and transferred from other genera:C. bisbinotata(Pic)comb. nov., transferred fromPlatylampisMotschulsky;C. decorata(Olivier)comb. nov., transferred fromEthraLaporte;C. pauper(Olivier)comb. nov., transferred fromCladodesSolier; as well asC. klugii(Motschulsky)comb. nov.,C. quadriguttata(Gorham)comb. nov., andC. tricolor(Gorham)comb. nov., transferred fromLucidotaLaporte.Costalampysgen. nov.is tentatively placed in Lampyrinae, and is diagnosed by: antennae with 11 articles, III–X basally flabellate, lacking dense and upright bristles; clypeus connected to frons by membrane, pygidium rounded; sternum VIII mucronate; phallus with dorsal plate enlarged apically, projecting ventrally and partially embracing the internal sac. Our phylogenetic analyses supported both the monophyly ofCostalampysgen. nov.and the new combinations proposed. However, the relationship among congeneric species was poorly resolved. Finally, we provide illustrations of diagnostic features, distribution maps, as well as a key toCostalampysgen. nov.species, based on males.