Quite rare. Also known as Belon (referring to the river in France that grows the finest), or Ostrea edulis, Flats are the native oyster of Europe. They are an entirely different genus from the rest of our oysters. They act different, and they taste different. Way different. Love ’em or leave ’em. They were introduced to Maine nearly a century ago and have gone wild in the estuaries there, where they are occasionally found by divers and clammers.