Trace your finger across Long Island, looking for great oyster geography, and east of Great South Bay you suddenly come across a perfect skillet-shaped bay, its handle poking into the Atlantic. This is Mecox Bay, home to weekend mansions and to a surprisingly robust population of wild oysters, perhaps the last in the region. Unlike shallow Great South Bay, Mecox is a deep hole, and its oysters flourish at thirty feet, where they stay cold and crisp. They grow slower, too, so a market-sized Mecox Bay is at least three years old, with a Fort Knox shell that makes it easier to shuck than any other Long Island oyster. As a wild oyster, a Mecox Bay can only be harvested in season, which runs from mid-November to the end of April. Its flavor is awfully mild, not salty, and oddly alkaline.