Crassostrea gigas—Pacific or Japanese oysters (West Coast)
These include Kusshi from British Columbia, which are small and meaty, similar to a Kumamoto. Another oyster in this family is the Marin Miyagi (Tomales Bay, Calif.). We're pretty sure these are not named after the affable sensei from "The Karate Kid," but they are super-creamy.
 Crassostrea sikamea—Kumamoto oysters (West Coast)
There's an old maxim that you shouldn't eat oysters in months without an "r" in their name, a.k.a the summer. With modern transportation and refrigeration, that's no longer true; however, during the summer domestic oysters aren't always as pristine as they are in winter. Fruity and buttery Kumamotos tend to stay sweet and firm even through the summer.
 Crassostrea virginicas—Atlantic oysters (East Coast and Gulf of Mexico)
These probably are the most ubiquitous oysters and include some of the most familiar names, such as Malpeque, Wellfleets, Blue Points and Beausoleils. These oysters generally are large, briny and metallic in flavor. They grow from New Brunswick, Canada, to Virginia, and also in the Gulf of Mexico—the further south, the bigger they get. Beausoleils are small, cold-water oysters, often with a nutty note that's great for novices. Small, sweet Apalachicolas from the Florida panhandle have appeared on local menus in recent years. Shigokus also are common; though the name sounds similar to "Chicago," these fatty, briny, deep-cupped oysters are from Washington state.
 Ostrea edulis—European flats (East and West coasts)
These are the beloved Belon oysters. You won't see European Belons in Chicago, but you may see Maine Belons or Maine Flats, which are ostrea edulis grown on America's Atlantic coast. Though you likely won't see them in on local menus, Westcott Bay Flats are ostrea edulis from Washington state's Puget Sound. These oysters are meaty, big and have a rich, mouth-coating flavor.
 Ostrea lurida—Olympia oysters (West Coast)
Tiny, almost thumb-sized Olympias are sweet and have a celery-like finish. These oysters are now rare and are thought to be disappearing because of ocean acidification and predatory snails.