The Achilia crassicornis, A. tumidifrons, A. bifossifrons, and A. lobifera species groups (sensuJeannel, 1962) of the species-rich genus AchiliaReitter, 1890 are revised. Of the twelve taxa previously placed in these four groups of species, two belong to different groups and will be treated in later papers (i.e. A. parvulaJeannel, 1962 and A. nahuelbutaeFranz, 1996 with the A. humidula and the A. cosmoptera groups, respectively), and five names are placed as junior synonyms: Achilia crassicornis antarcticaJeannel, 1962 and A. obscuraJeannel, 1962 = A. crassicornisJeannel, 1962 (syn. nov.); Achilia tumidifronsJeannel, 1962, A. globicepsJeannel, 1962 and A. paraglobicepsFranz, 1996 = A. larvata (Reitter, 1885) (syn. nov.). The lectotype and paralectotypes of A. larvata are designated. The five species left in these groups are redescribed, their distributions are detailed, and habitats/collecting data are summarized.