Shells of Heterogen japonica (Martens, 1861), H. longispira (Smith, 1886), and the intermediate morphology between the two species stored at the National Museum of Nature and Science, Tokyo, which were treated as Viviparus sclateri (Frauenfeld, 1865) in Iwakawa's catalogue (1919). a-b: H. japonica in 2969J from Otsu City, Shiga Pref. c-d: non-typical H. longispira in 2969L from Otsu City, Shiga Pref. e: typical H. longispira in 2969L from Otsu City, Shiga Pref. f: subadult H. japonica in 2969J from Otsu City, Shiga Pref. g-j: non-typical and intermediate H. longispira in 2970L from the Seta River, Shiga Pref. K: typical H. longispira in 2970L from the Seta River, Shiga Pref. l: a juvenile shell of H. japonica in 2970J from the Seta River, Shiga Pref. m: a typical juvenile shell of H. longispira in 2970L from the Seta River, Shiga Pref.