Amydetinae is an exclusively Neotropical subfamily of fireflies, distributed among three genera: Amydetes Illiger, 1807, Magnoculus McDermott, 1964, and Memoan Silveira & Mermudes, 2013. Here, we describe three new species of Amydetinae : two belonging to Amydetes ( A. alexi sp. nov. and A. marolae sp. nov.) and one to the previously monotypic Memoan ( Me. conani sp. nov.). All three species are known only from the Atlantic Forest in southeastern Brazil. Endoskeletal structures of Memoan and Magnoculus species are described and compared with those of Amydetes for the first time. After studying the type material, Photinus fruhstorferi Pic, 1942 is transferred to Memoan , generating Memoan fruhstorferi comb. nov., and Me. ciceroi Silveira & Mermudes, 2013 syn. nov. is placed as a junior synonym. We also redescribe Magnoculus obscurus Olivier, 1885 and compare it to other species of genus and to other amydetine taxa to identify potential new diagnostic traits for the Amydetinae and its constituting genera. We provide an updated diagnosis for Memoan , illustrations for all four species, and a distribution map for the three new species, as well as a key to adult males of the three amydetine genera, and an updated key to Amydetes species based on males.