Assertion: periwinkle | /r/AtLocation | rock
Facets:
value: usually
type: DEGREE
Source sentences:
text: Periwinkles are widely distributed shore (littoral) snails, chiefly herbivorous, usually found on rocks, stones, or pilings between high- and low-tide marks; a few are found on mud flats, and some tropical forms are found on the prop roots or mangrove trees.