Oxychilus alliarius (Miller, 1822) and O. helveticus (Blum, 1881), two west European species sometimes confused with each other, are redescribed. Their identification is easy, but requires both conchological and anatomical characters. The two species are readily distinguished by shell shape and size and internal ornamentation of the penial complex. O. alliarius has a smaller shell (shell diameter: 4.5 - 7.0 mm) with a proportionately larger umbilicus (about 1/6 of shell diameter), usually lacks blackish mantle edge and has internal ornamentation of proximal penis consisting of not more than four longitudinal pleats, usually straight, sometimes slightly wavy, but never laterally branched or papillate. O. helveticus has a larger shell (shell diameter: 7.3 -12.2 mm) with proportionately smaller umbilicus (about 1/8 of shell diameter), a blackish mantle edge and internal ornamentation of proximal penis consisting of more than seven longitudinal pleats, sometimes straight and distinct, sometimes wavy, slender and connected by lateral projections giving a reticulate appearance.