The Cretaceous Jurassic (Oxfordian stage) aged cliffs near Villers Sur Mer are the source for these Trigonia dillatata clavellata pelecypods. Trigonia shells can be noted for their unique shape and shell decoration which varies from species to species.
This is a smaller but less worn example of the species.
Thanks to Gery for sending me these specimens and for correcting me on the species and age. I get confused sometimes trying to keep track of the Cretaceous and Jurassic stages. :)