This paper is a supplement to the author’s earlier synopsis (Kuiper, 1962) on Pisidium pseudosphaerium Schlesch. During the last ten years it has been discovered in Ireland, Denmark, Finland, SE. Czechoslovakia, Austria (Salzburg, Kärnten), N. Italy (Lombardia). Fossil occurrence has been reported from the Pliocene (Germany, Turkey) and the last Interglacial (Germany). Its Recent range as far as known extends from 7°W (Dublin, Ireland) to 31°E (Leningrad, U.S.S.R.), and from 44°N (Toulouse, France) to 61°N (Tampere, Finland). Most localities are situated below 300 m.s.m.; the highest locality known is at about 475 m in SE. Czechoslovakia.