The taxonomy of the freshwater crabs of Madagascar is revised and the number of genera raised from five to six. Two new genera are erected and one genus is synonymised. Hydrothelphusa is revised with four species: H. agilis A. Milne-Edwards, 1872, H. madagascariensis (A. Milne-Edwards, 1872), H. bombetokensis (Rathbun, 1904) and H. goudoti (H. Milne Edwards, 1853) n. comb. Malagasya n. gen. is established to accommodate two species, M. antongilensis (Rathbun, 1905) and M. goodmani (Cumberlidge, Boyko & Harvey, 2002); Marojejy Cumberlidge, Boyko & Harvey, 2002 and Madagapotamon Bott, 1965 are recognised as monotypic genera, Skelosophusa remains unchanged, and Boreas n. gen. is established for one species B. uglowi n. sp. The genus Gecarcinautes Bott, 1960 is here synonymised with Potamonautes Macleay, 1838 and its former taxa are referred to other genera. All six genera of freshwater crabs found in Madagascar are endemic and all are here referred to the Potamonautidae. A new diagnosis for each of the 12 species is provided, many are redescribed, and most are figured from the type. Keys to the genera and species of the Madagascan freshwater crabs are provided, together with species distribution maps and a gazetteer.
Crustacea, Decapoda, Brachyura, Potamoidea, freshwater crabs, Madagascar, identification keys, new genera, new species.