The taxonomic identity o/Valvata ambigua Westerlund 1873 has been examined by using the type materials and samples of snails collected in Europe (Northern Germany) and Western Siberia. V. ambigua is considered to be a distinct species closely allied to Valvata piscinalis O.F. Müller 1774. It can be distinguished from the latter by differences in shell shape and growth patterns. The characteristic features of the two species are stable under conditions of syntopy and therefore these can be regarded as two biologically meaningful entities, or biospecies. The range of V. ambigua covers north, central and eastern Europe and the south part of western Siberia.