Revision of the Neotropical subgenera Coelioxys (Platycoelioxys) Mitchell and C. (Rhinocoelioxys) Mitchell (Hymenoptera; Megachilidae) with the description of one new species.

Two Neotropical subgenera of Coelioxys Latreille are revised. The monotypic C. (Platycoelioxys) Mitchell and C. (Rhinocoelioxys) Mitchell has seven valid species; six of them (C. agilis Smith, C. barbata Schwarz & Michener, C. clypearis Friese, C. nasidens Friese, C. paraguayensis Schrottky and C. zapoteca Cresson) previously described, and one, C. platygnatha Rocha-Filho & Packer n. sp. is new from Amazonas State, Brazil. Coelioxys nasidens, previously considered a junior synonym of C. clypeata Smith, is resurrected. Coelioxys crassiceps Friese and C. excisa Friese are synonymized under C. agilis, and C. rostrata Friese is synonymized under C. paraguayensis. Nine names (C. clypeata, C. leucochrysea Cockerell, C. angustivalva Holmberg, C. doelloi Holmberg, C. blabera Holmberg, C. mesopotamica Holmberg, C. bilobata Friese, C. bilobata schenki Friese and C. bullaticeps Friese) are synonymized with C. zapoteca. In the latter species the shape of the apical margin of the clypeus of the female varies widely and, though intermediates occur among all forms, the DNA barcode sequences for the different forms are very similar. One species formerly considered as incertae sedis, C. clypearis, and one belonging to the subgenus C. (Cyrtocoelioxys) Mitchell, C. barbata, are both assigned to the subgenus C. (Rhinocoelioxys). Keys for both sexes of C. (Rhinocoelioxys), distribution maps, host and floral records, redescriptions of species and the description of a new species are provided. In the subgenus C. (Platycoelioxys), only one species, C. alatiformis Friese, is recognized with two junior synonyms: C. crassiceps Friese syn. nov. and C. spatuliventer Cockerell.