The taxonomy of the genus Bulinus is re-examined on the basis of morphology and of electrophoretic study of 20 gene-enzyme systems. The genus is at present divided into two subgenera: Bulinus and Physopsis. According to Mandahl-Barth the first subgenus is made up of three groups of species (the tropicus, truncatus and forskalii groups), while the species of the second subgenus are united in a fourth group (africanus). We have studied various species and subspecies belonging to the two subgenera and to Mandahl-Barth's four groups of species: abyssinicus, africanus, alluaudi, forskalii, globosus, guernei, jousseaumei, natalensis, rivularis, rohlfsi, senegalensis, tropicus, truncatus and yemenensis. Enzymes encoded by 20 loci were examined as follows: Esterases (Est-1, Est-2, Est-3, Est-4), $\alpha$-Glycerophosphate dehydrogenase ($\alpha$-Gpdh-1, $\alpha$-Gpdh-2), Isocitrate dehydrogenase (Idh-1, Idh-2), Octanol dehydrogenase (Odh), 6-Phosphogluconate dehydrogenase (6-Pgdh), Sorbitol dehydrogenase (Sdh), Xanthine dehydrogenase (Xdh-1, Xdh-2), Phosphoglucomutase (Pgm-1, Pgm-2), Adenylate kinase (Adk-1, Adk-2), Phosphoglucoisomerase (Pgi), Glutamate oxaloacetate transaminase (Got) and Superoxide dismutase (Sod.) Nei's index was used to estimate the genetic distance between populations studied. The results substantially confirm the systematic validity of the three groups africanus, truncatus and forskalii proposed by Mandahl-Barth, while the tropicus group appears phylogenetically related to the truncatus group. We therefore propose dividing the genus Bulinus into three genera described as follows: Bulinus Müller, 1781, for the species with long-spired shells, without ridge on the ventral surface of the kidney and with copulatory organ present, widely distributed in Africa and also present in Madagascar. Some of these species are considered vectors of Schistosoma haematobium. Type species: Bulinus senegalensis Müller, 1781. This genus substantially corresponds to Mandahl-Barth's forskalii group. Physopsis Krauss, 1848, to indicate the species with wide-spired shells with characteristic microsculptures on the upper whorls and a ridge on the ventral surface of the kidney. Important vectors of S. haematobium South of the Sahara. Type species: Physopsis africana Krauss, 1848. This genus substantially corresponds to Mandahl-Barth's africanus group. Mandahlbarthia gen. nov., to indicate the species with generally wide-spired shells, without microsculptures on the shell, having lateral teeth with broad arrowhead-shaped mesocones, without ridge in the ventral surface of the kidney, frequently aphallic. Present in the Mediterranean region, Middle East and vast areas of tropical and subtropical Africa. This genus includes important vectors of S. haematobium. Type species: Mandahlbarthia truncata (Audouin, 1827). This genus substantially corresponds to Mandahl-Barth's truncatus and tropicus groups. We propose the new name Mandhalbarthia because the use of the old name Isidora Ehremberg, 1831 is problematic and may be a source of confusion. Nor can the name Pyrgophysa Crosse, 1879, whose type species P. mariei clearly belongs to the forskalii group, be used. We consider these as genera rather than subgenera for the following reasons: 1) their marked morphological differences; 2) the very high values of average genetic distance ($\bar{D} > 2.5$) observed among the three groups; 3) evidence of subgeneric differences within the proposed genera. Finally, it should be underlined that M. rohlfsi and M. rivularis, so far considered subspecies of M. truncata, as well as M. alluaudi, so far considered a subspecies of M. tropica, appear to be genetically well-differentiated species.