A small mollusc-fauna is described from a temporary excavation in the middle part of the Atuatuca Formation near the town of St.-Truiden. The following species were encountered: Hydrobia elongata (Faujas de St.Fond), Mercuria helicella (Braun), Nystia (Nystia) plicata (d’Archiac & de Verneuil) sensu Glibert & de Heinzelin, 1954, Hydrobiidae gen. et sp. indet., Lymnaea longiscata (Brongniart), Radix (Radix) sp. and Gyraulus (Gyraulus) acuticarinatus vleminckxae n. subsp. Nystia (Nystia) glibertheinzelini n. sp. is introduced from heavy clays in the Atuatuca Formation (localities Grote Spouwen, Outershoven and Rosmeer). The stratigraphical position and the palaeoecology of the fauna are discussed.