121 pages : illustrations (some color), maps ; 26 cmThe Neotropical chactid scorpion genus Chactopsis Kraepelin, 1912, is revised. New diagnoses are presented for all previously described species, most of which have not been revised since their original description. The trichobothrial pattern is reinterpreted and the hemispermatophore described for the first time. Chactopsis is restricted to eight species, two of which are new: Chactopsis chullachaqui, n. sp., from Peru and Chactopsis curupira, n. sp., from Brazil. Chactopsis insignis Kraepelin, 1912, is redescribed and supplementary data on pedipalp trichobothria and hemispermatophore (where known) provided for Chactopsis amazonica Lourenço and Francke, 1986, Chactopsis barajuri González-Sponga, 1982, Chactopsis buhrnheimi Lourenço, 2003, Chactopsis siapaensis González-Sponga, 1991, and Chactopsis sujirima González-Sponga, 1982. Two new genera are created to accommodate the remaining species, formerly assigned to Chactopsis, based on a cladistic analysis of morphological characters. Chactopsoides, n. gen., accommodates Chactopsoides anduzei (González-Sponga, 1982), n. comb. (type species), and Chactopsoides marahuacaensis (González-Sponga, 2004), n. comb., Chactopsoides gonzalezspongai, n. sp., from Venezuela, and Chactopsoides yanomami (Lourenço et al., 2011), n. comb., from Brazil. Chactopsoides anduzei, n. comb., is redescribed and Chactopsis carolinae Botero-Trujillo, 2008, synonymized with it. Supplementary data on pedipalp trichobothria are provided for C. marahuacaensis, n. comb. Megachactops, n. gen., accommodates Megachactops coriaceo (González-Sponga, 1991), n. comb., and Megachactops kuemoi, n. sp. (type species), from Venezuela. Supplementary data on pedipalp trichobothria and hemispermatophore are provided for M. coriaceo, n. comb. A key to identification of the species of Chactopsis, Chactopsoides, n. gen., and Megachactops, n. gen., is provided, their morphology illustrated, and distribution records mapped