CALIFORNIA MUSSEL Mytilus californianus Conrad, 1837: 242; M. californicus auct, nom. null; M. edulis giganteus von Nordmann, 1862: 422, ex Homberg MS. Large, thick, elongate; dorsal margin slightly expanded. Sculpture of radial ribs and irregular commarginal crenulations. Shell and periostracum thicker than in either M. trossulus or M. galloprovincialis. Length to 251 mm. The species is found on exposed rocky foreshores and forms dense beds. It is also known in subtidal beds in 100 m or more, and is a dominant animal on many sea- mounts. The byssus furnishes a strong, flexible attachment for the shell to withstand wave surge. The species is limited to the northeastern Pacific. It occurs from Cook Inlet, Alaska (59.2°N) [LACM], to Punta Rompiente, Baja California Sur (27.7°N) [LACM], with an isolated population on Isla Socorro, Islas Revillagigedo, México (18.8°N) [LACM], in the intertidal zone to 50 m, in areas offering some protection from predation. Known as early as the Pliocene of California.