The distribution of the American jack-knife clam Ensis directus (Conrad, 1843) (photo 1, figure 1,2) in Europe is discussed. The first specimens of this North- American species were found in 1979 in the German Bight, near the mouth of the river Elbe (Von Cosel et al., 1982). Most probably larvae were transported to Europe in 1978 with tanker ballast water. At present, about 23 years later, E. directus has spread considerably along the Western-European coasts. Towards the north (table 2, figure 3) it is found up to Oslo in Norway, has spread all around the Danish coast up to the south-western part of the Ostsea and occurs also along the west coast of Sweden. Southward (table 1, figure 3) it is found on the beaches of The Netherlands and Belgium, in the south-eastern part of England (from the Humber estuary southward along the east coast to Newhaven at the English channel coast (Eno, 1998) and along the French coast as far south as Merville-Franceville (south of Le Havre) in Normandy (Severijns, 2000a, 2000b). Most probably the species will continue to further extend its area of distribution, as in different parts of it suitable habitats are within reach. The possible influence of E. directus on the occurrence of the local European Ensis and Solen species was discussed. Observations indicate that E. arcuatus (Jeffreys, 1865) and E. minor (Chenu, 1843) do not occur any more at the Belgian coast. Indeed, no significant quantities of fresh specimens have been found on Belgian beaches since 1997. Before, both species were very common and until 1997 relatively large amounts (for E. arcuatus even up to several hundred specimens at a time) were regularly washed ashore (e.g. Rappé, 1985, Severijns, 1994, 1996; Vanhaelen, 1997a, 1997b, 1998). Solen marginatus , has never been a common species at the Belgian coast, but from time to time, especially af ter several consecutive soft winters, populations of Solen marginatus do occur. In the past 15 years three strandings occurred: in the period April-September 1985 (several ...