Because of their rare occurrence complete specimens of the fossil flask-shell (Gastrochaena dubia) are seldom collected from the Tertiairy beds near Antwerp, Belgium. However, a number of specimens were found in their own bore-holes, which were made in a stone-like substratum (septaria). The species is not exclusively dependent on stone substratum; it may also choose a large shell to settle and then complete the bore-hole by a self-built tube if the shell-material is not thick enough for the animal. Recently a nice specimen was found in a valve of Pygocardia rustica from Pliocene beds (Kattendijk sands) near Antwerp. The outside of this valve show s an opening in the shape of an 8, to permit the passage of the sipho’s. This suggests that there is a well-preserved Gastrochaena inside the valve.