The identity of a fossil valve with a colour pattern from the Pliocene of the northern Peel district, the Netherlands (Bivalvia, Pectinidae)

The identification of a fossil valve as Pseudamussium (Palliolum) gerardi (Nyst, 1835) with a colour pattern (Van der Burg, 1995: 29-30) has been questioned by Janssen & Dijkstra (1996: 107- 113), who are of the opinion that the valve belongs to Palliolum tigerinum (Müller, 1776). It could, however, be shown that “a light-coloured part near the umbo” on P. gerardi, thought by these authors to be the specific colour pattern of this species, is not a colour pattern but the image of a corrosion remnant of the inner layer of the valve, visible through the thin transparent outer layer. This peculiarity is encountered in a number of valves, but, of course, not in dark-coloured ones as the valve in question. In addition, the types of colour patterns on shells of Recent P. tigerinum (cf. Janssen & Dijkstra, 1996: 110) cannot contribute to the identification of our fossil, since they are widespread among living bivalves of unrelated species. Finally, the identity of our valve as P. gerardi could be confirmed by using the table “Comparison between Palliolum tigerinum and Palliolum gerardi”, recently published by the same authors who questioned this identity.