Periwinkles are a family of marine snails. They are popularly consumed in Europe and the Far East, but they have not caught on as regular menu items in the U.S. Recently I happened upon a bag of frozen cooked periwinkle meat in market near San Francisco. Traditionally, periwinkle eaters have extracted the cooked meat from the shells with a special two-tined fork or, if forced to improvise, a toothpick. Having the meat extracted is a convenience.