The name Arion hortensis has been used for three different British species of slug, called A, R and B by Davies (1977). Arion (Kobeltia) hortensis Férussac s. s. is defined as having the anatomy and spermatophore of form R. A. (K.) distinctus Mabille is identified as form A, and is thus given an anatomical definition. External features are discussed with reference to original descriptions and identification. Form B becomes A. (K.) owenii sp. nov.