De Gekielde clausilia Macrogastra rolphii op, en de Geribde clausilia Macrogastra attenuata lineolata bij de Sint-Pietersberg in Maastricht

Together with four more Clausiliidae Macrogastra rolphii is common on the eastern slope of the cretaceous Sint- Pietersberg in Maastricht (province of Limburg). Recently, within 50 m from that locality a population of Macrogastra attenuata lineolata was discovered living on the inner side of the dike along the river Maas. Described habitat preferences of both species are reviewed in an attempt to explain why these sibling species are here “living apart together”.