Genus Leucos Heckel, 1843

Type species: Squalius aula Bonaparte, 1841: Fauna It., fasc. XXX, Tav. 116, fig. 3: type locality; Padua Province; north-eastern Italy.

Leucos cisalpinus Heckel, 1843: 1081 (Lake Garda) was the subsequent type species designation by Jordan & Gilbert (1883). But it was a nomen nudum. Type species by present designation: Squalius aula Bonaparte, 1841: type locality; Italy, Padua Province, north-eastern Italy. It is the only species from Lake Garda, common in every lake of northern Italy, which corresponds with the short description below of the genus. A short diagnosis (translated from Latin) of this genus was given by Heckel, (1843:1081): pharyngeal teeth, 5-5; mouth small; lips smooth; barbels absent; dorsal and anal fins short; origin of D at level of insertion of pelvic fins. Others species placed by Heckel (1843) in this genus: Leucos rubella Heckel, 1843 (nomen nudum); Leucos basak Heckel, 1843; Leucos (now placed in Delminichthys) adspersus Heckel, 1843, Leuciscus selysii Selys-Longchamps, 1841 (junior synonym of Rutilus rutilus); and Leuciscus rutiloides Selys-Longchamps, 1842 (junior synonym of R. rutilus). The genus Leucos was used by several authors until it was synonymized with Rutilus (Howes, 1981) .

Diagnosis. Distinguished from others genera of European cyprinids by a combination of the following characters: pharyngeal teeth 5-5 (rarely 4-5 or 5-4 or 6-5) hooked and slightly serrated. Mouth small, terminal or slightly upturned or downturned; origin of D nearly at same level of origin of P2; free margin of D and A concave or slight concave; caudal fin from moderately to deeply forked; peritoneal membranae from silvery to blackened by fused melanophores; body without longitudinal stripes (excepted Leucos aula). GR short. Usually, 8–9 branched rays in the D and in the A; 8 branched rays in the P2; 12–14 circum-peduncular scales; absence of large pearl organ (nuptial tubercles) on head and central part of scales in reproductive males; small size, did not exceed 180 mm SL; mostly a still water species. Sequence variation of the entire mitochondrial cytochrome b gene shows a strictly relationship among five species, which separated from a Leuciscinae ancestor about 4-5 milion years ago, during the Lago Mare phase of the Mediterranean (Bianco, 1990), probably following the same evolutionary trajectories of the genus Telestes, which occurs in the same geographic area (Ketmaier et al., 2004).