During a dive I found these butter clam (Saxidomus gigantea) shell valves still attached and resting on the sand in a protected bay. The valves have well developed concentric ridges, and there is a large black external hinge ligament between them. There are also three cardinal hinge teeth on each valve, and the interior surfaces of the valves are smooth but not glossy. This clam can live for more than 20 years, and is commercially harvested for clam chowder. The butter clam has a range from northern Alaska to southern California.