In 1907 Mr. Caesar R. Boettger 1) called attention to the fact that this species, an inhabitant of the North-American seas, since the last decennium of past century is spreading on the European coast. In Europe it was found first in England at Cricksea on the river Crouch, in July 1890 2), and on the Lincolnshire coast 3). The following years brought further references about the occurrence of Petricola pholadiformis on the English coast 4). At present the localities where it is found, stretch from Shellness, near Sandwich, Kent, in the south, to Mablethorpe, Lincolnshire, in the north. Mr. Loppens 5) was the first to notice this species on the continent; he found it near Nieuwpoort on the coast of Belgium, in 1899. Very soon afterwards other localities were known where Petricola pholadiformis occurred on the Belgian coast 1), and also at Dunkerque 2) in France. In June 1906 Miss H. Icke (presently Mrs. Martin—Icke) found this species on the Dutch coast near Noordwijk 3). In the same year it was noticed by Mr. Caesar R. Boettger 4), by Mr. E. Wolf 4) and by the Rev. Ricklefs 5) on different points near the German coast, from the Dutch till the Danish frontier. Mr. Julius Pfeffer 6) mentioned the occurrence near Hooge, a small North Frisian island, south of Föhr, and stated the fact that this species never occurred there before 1906. Finally Mr. H. Schlesch 7) obtained it in 1907 from Fanö and Manö, two Danish islands. Seeing thus, that Petricola pholadiformis has a rather wide distribution on the North-Sea-coast, and that it is found rather abundantly near our frontiers, I expected a priori that Mrs. Martin’s statement should not remain the only one. When examining the collections of shells from our country, acquired by the „Rijks Museum van Natuurlijke Historie” during the last years, I actually found several specimens of Petricola pholadiformis from various localities along the coast. They are the following: Domburg, isle of Walcheren, 1905, Mr. W. C. van Heurn; 1912, Mr. J. H. Vernhout. Renesse, isle of Schouwen, 1911, Mrs. H. Martin—Icke.