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Rh centric sculpture of fine, irregular threads. Periostracum remaining on the margins is gray. Pallial sinus in left valve runs from the posterior muscle scar anteriorly toward the anterior muscle scar, but does not meet the latter, and then descends posteriorly to meet the pallial line about the middle of the lower margin of the shell. A common cold-water species, distinguished from balthica by its larger size, more elongate shape and pattern of the pallial sinus scar (see fig, 88g).

Figure 88. American Macomas, showing interior scars, a, Macoiua brota Dall, 3 inches (Alaska to Washington); b, M. incongnm von Martens, i inches (Alaska to Washington); c, M. secta Conrad, 3 inches (Pacific Coast); d, M. nasuta Conrad, 2 inches (Pacific Coast); e, M. inis Hanley, 2 inches (Pacific Coast); f, M. calcarea Gmelin, 2 inches (Atlantic and Pacific Coasts); g, M. balthica Linne, i inch (Atlantic and Pacific Coasts); h, M. planhisciila Grant and Gale, i inch (Alaska to Washington). Macoma balthica Linne Balthic Macoma Figure 88g Arctic Seas to off Georgia. Bering Sea to off Monterey, California. % to 1/4 inches in length, oval, moderately compressed. Color dull whitish, in some with a flush of pink, and with a thin, grayish periostracum which readily flakes off. The shape is somewhat variable. A common inter- tidal and deep-water species. Compare muscle scars with those of calcarea. Macoma tenta Say Tenta Macoma Cape Cod to south half of Florida and the West Indies.