In this article, the subgenus Canthon (Goniocanthon) Pereira & Martínez, 1956 is diagnosed within the tribe Deltochilini Lacordaire, 1856 and redefined with three species: 1) C. (Goniocanthon) bicolor Castelnau, 1840, from the Guyanas and northern South America, included for the first time in this subgenus; 2) C. (G.) smaragdulus (Fabricius, 1781), including two subspecies, C. (G.) smaragdulus smaragdulus, senior synonym of Canthon speculifer Castelnau, 1840 (neotype here designated), from the southern portion of the Atlantic Forest and C. (G.) smaragdulus subviridis Schmidt stat. rev. (lectotype here designated) from the northern portion of the Atlantic Forest; 3) C. (G.) fulgidus Redtenbacher, 1868, which includes three subspecies, C. (G.) fulgidus fulgidus from the southern Amazon (lectotype here designated), C. (G.) fulgidus martinezi subsp. nov., from the central and southern Amazon and C. (G.) fulgidus pereirai subsp. nov., from the western Amazon.