Pachymesia Westwood (1849) and Incisosilis Pic, 1908 are small Neotropical genera of Silinae distinguished by subtle morphological differences in males. They include, respectively, two species and four species and one subspecies recorded from the Atlantic Forest of Brazil and Guatemala. Here, both genera are revised and Incisosilis is regarded as a new synonym of Pachymesia, new combinations are proposed, the subspecies is elevated to species rank, and nine species are described as new, comprising 16 valid species in total: Pachymesia incisa Westwood, 1849, P. testaceicornis Pic, 1908, P. latipennis (Pic, 1908) comb. nov., P. distinctithorax (Pic, 1908) comb. nov., P. pallida (Pic, 1912) comb. nov., P. subacuminata (Pic, 1912) comb. nov., P. subopaca (Pic, 1913) comb. nov., P. inspinosa sp. nov., P. terminalis sp. nov., P. laeta sp. nov., P. constricticornis sp. nov., P. singulariventris sp. nov., P. emarginata sp. nov., P. lawrencei sp. nov., P. fuscohumeralis sp. nov. and P. laranjensis sp. nov. The genus is recorded for the first time in Argentina (Misiones province) and the unreliable record from Guatemala is corrected to Espírito Santo state in Brazil based on the study of additional specimens. All the species are described and illustrated; photographs and drawings are given for all the species and their diagnostic features; the wing and genitalia of males and females of Pachymesia are illustrated for the first time. The morphology of the genital segments and genitalia of males are reinterpretated and a new terminology for the structures is proposed. The unusual morphology of the abdomens of males and females is suggested as having a role in the reversed copulatory courtship displayed by some Silinae. Pachymesia is broadly distributed in the Atlantic Forest of Brazil and Argentina though unevenly sampled through this biome, suggesting the diversity of the genus is still far from being fully known.