FOOLISH MUSSEL Mytilus trossulus A. A. Gould, 1850c: 344; 1852: 450; 1860: pl. 41; M. glomeratus A. A. Gould, 1851:92; 1853: 402; M. pedroamus Conrad, 1855b: 15; M. edulis "normalis" Carpenter, 1857b: 197; M. e. latissimus Carpen- ter, 1857b: 197; M. septentrionalis Clessin, 1887: 58; M. ficus Dall, 1909a: 113; M. (Mytilus) edulis kussakini Scarlato and Starobogatov, 1979a: 109; M. edulis declivis Petrov, 1982: 77. Shell trigonal, flared, outline variable, frequently expanded dorsally, as in M. galloprovincialis. Ventral surface relatively wide laterally; anterior end pointed, often curved. Hinge plate dark to light in color, curved. Anterior adductor muscle scar relatively small; posterior byssal retractor muscle scar relatively long, narrow. Length to 90 mm. This species and M. galloprovincialis cannot be distinguished with certainty based only on shell characters. Some guesswork is involved in the listing of synonyms, based on the assumption that Mytilus galloprovincialis was introduced into the eastern Pacific after 1900. Clearly, more study is necessary. In the Arctic from Banks Island, Northwest Territories (72.0°N), west to Point Barrow, Alaska (71.4°N) [LACM], throughout the Bering Sea, south to central California, and probably sporadically to southern California (about 33.5°N), where it has been displaced by M. galloprovincialis. From central California southward, forming hybrids with M. galloprovincialis. Westward throughout the Aleutian Islands to Siberia, and probably to northern Japan. Also with disjunct populations in northeastern Canada and the Baltic Sea. In the intertidal zone, on rocks and pilings. Records from as far back as the Miocene in western North America are probably this species. Literature: D. P. Abbott and Hilgard (1987: 182), Blanchard and Feder (1997), Buianovskii (1992), Culotta (1995), U. S. Grant and Gale (1931: 244-245), J. H. McDonald and Koehn (1988), N. L. MacGinitie (1959: 157), E. J. Moore (1983: 61), Scarlato (1960: 92-94, 1981: 245-246), Seed (1992). See also literature listed below.