Ensis directus occured for first time in high number in the French par
t of the North Sea in spring 1991. Identification of specimens smaller
than 15 mm is difficult because of easy confusion with Ensis arcuatus
. For longer animals, a length/height ratio of 6:1 is a reliable crite
rion of identification for Ensis directus after the three other consta
nts and reliable characters described by de Boer (1984).