In 1962 Dr. P.E.P. Norton, at that time investigating the fossil Mollusca of the Royal Society Borehole at Ludham, East Anglia, at the University of Cambridge, handed me two right valves of a very small bivalve shell, which he was unable to identify. I myself was not able to classify the valves with any known genus either. Later on the Geological Survey of the Netherlands started intensive investigations of the so-called Dutch Continental Shelf of the North Sea, which investigations were also extended to the Strait of Dover. Many borings were made and many bottom samples were taken from the surface of the seabottom over the whole area investigated. A large number of these borings and bottom samples were examined for molluscs by the author and his assistants, especially Miss Nettie Deen. To my astonishment many valves of the unknown species of the Ludham borehole were found to be present in the samples investigated, many of them very fresh-looking, with vitreously transparent shells.