Brown Atlantic Clams

• If you live along the Atlantic shore, or if your local fishmonger's suppliers are there, the clam you'll see most often is the brown-shelled quahog. They're sold under a variety of names, depending on their average size, so whether you're buying littlenecks, cherrystones or chowder clams they're all quahogs. Softshell clams are typically larger, and have a long, droopy siphon or "foot" dangling from one end of the shell. The foot is edible but chewy, so it's usually cut into strips for cooking. Razor clams are even more distinctive, with a rectangular shape resembling an old-fashioned straight razor, and have an unusually sweet, lobster-like flavor.

White Atlantic Clams

• Quahogs can also sometimes have pale or white shells, but you're more likely to see them on ark clams. They're small and limited in availability, but have good flavor and are worth digging if you live near the shore. The other Atlantic clam that commonly has a white shell is the surf clam, harvested usually from waters 100 to 200 feet deep. They're large, often 6 to 7 inches across, with a large and lobster-red foot or "tongue." The chewy tongue is cut into strips for frying, while the softer belly meat is chopped for use in chowder and seafood medleys.

Brown Pacific Clams

• Dark-colored clams are less prolific on the Pacific coast, and lean as much to gray as brown. The most distinctive are the cockles, which have an attractive brown color and a strong scallop-like pattern of ribbing running from the hinge to the edge of the shell. Horse clams and softshell clams can run a range of browns and dirty grays, and horse clams have a distinctive foot at the digging end.

White Pacific Clams

• White-shelled clams include some of the most popular, such as the small and flavorful butter clam. The sand clam is similar but more oval, leaning to a pale tan hue rather than pure white. The Pacific Northwest's native littleneck clam is pale and tasty, and the Manila clam -- an invasive imported species, but now valued in its own right -- closely resembles it in appearance and flavor. The ribs on their shells are about as visible as their growth rings, giving the shells a distinctively crosshatched texture. Manilas are subject to some individual variation, and some look more brown than white.