n.
In zoology, any of some 80 species (family Littorinidae) of widely distributed, chiefly herbivorous shore snails .
Periwinkles are usually found on rocks, stones, or pilings between high-and low-tide marks. The common periwinkle ( Littorina littorea ), the largest northern species, may grow to 1.5 in. (4 cm) long. It is usually dark gray and has a solid spiral shell. Introduced into North America 0441; 1857, it is now common on Atlantic coasts. All periwinkle species are a favourite food of many shorebirds.
Periwinkles ( Littorina )
Jane Burton
Bruce Coleman Ltd.