Een pisidiologische excursie langs de Geer (Jeker) in België

In 1942 Venmans collected several Pisidium species in the river Jeker near Maastricht. Among these were several P. tenuilineatum. Recently the river Jeker on the Belgium side (there called ’Geer’) was sampled with negative results: apart from 1 specimen of P. personatum, no Pisidiums were found. The Geer nowadays is a very polluted river.