This clam is found from Alaska to California. The shells are large (up to five inches in length), heavy, oval to square-shaped and externally marked with concentric rings, but without radiating ridges. They are yellow in color when young, changing to gray-white with age. When disturbed, the clam withdraws completely within the shell, leaving a slight opening between the valves in the area of the siphon or neck. Butter clams are normally buried in the substrate between 8-14 inches; sport diggers use shovels or forks. They prefer sand-gravel beaches and are concentrated in the lower intertidal and shallow subtidal zone. Some beds have been located in water as deep as 60 feet. They are an important commercial and sport clam. Many people consider them the best for chowder. Butter clams have a tendency to accumulate and retain PSP toxins, so be sure to check the Department of Health's PSP hotline (1-800-562-5632) before harvesting. Commercially, they are dug intertidally by hand during low tides and by mechanical harvesters in deeper water. A large portion of the commercial catch is canned. They spawn in the summer. Experiments indicate that water temperatures of about 70' F are required for spawning in the laboratory. Three to four weeks are needed to complete the larval period in laboratory cultures.