The American sciaenid genus Macrodon presently consists of only two species, the Atlantic Macrodon ancylodon (Bloch & Schneider, 1801), and the Pacific Macrodon mordax (Gilbert & Starks, 1904). The two species are distinguished mainly by the number of pored scales on the lateral line (66–78 in M. ancylodon vs. 45–55 in M. mordax). The present study revalidates a third species, the second from the Atlantic, Macrodon atricauda (Günther, 1880), which is genetically, morphologically, and geographically distinct from M. ancylodon, occurring between the Brazilian state of Espírito Santo and northern Argentina. It has significant economic importance in the area and thus considerations about its conservation are also presented.