A Habit of the Common Periwinkle (littorina littorea Linn.)

Abstract

AN interesting habit of the common periwinkle, Littorina littorea Linnæus, which does not appear to have been recorded by previous writers, is worthy of some attention. On boulder-strewn shores, such as that at Penrhyn Bay, North Wales, where these observations were made, this species may occur in enormous numbers at and below the half-tide level in situations devoid of the larger Fucoid algæ. The boulders are covered with barnacles and afford no shelter from the sun except on the north side or in shady crevices. The periwinkles, nevertheless, cling in closely packed rows to the sides of the boulders, especially near the base where it is damp, but also higher up, and they may become completely dried on a hot day.