Populations on the west coast of Anglesey are nigrolineate with the dark lines confined to the spiral grooves (left half of image), while those on the north coast nearly all lack dark lines. As there is no planktonic veliger stage and it is an intertidal species there is little opportunity for gene exchange between populations. The ground colour grades from white to pale yellow on both populations. Several of those on the left also have much pale grey.  Anglesey, Wales. March 2015.