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Family MOPALIIDAE Genus Mopalia Gray 1847 Mopalia ciliata Sowerby Hairy Mopalia Alaska to Monterey, California. I to 1% inches in length, oblong, usually colored with splotches of black and emerald-green, although sometimes having cream-orange bands on the sides of the valves. Sometimes grayish green with grayish black or white mottlings. Girdle colored yellowish brown to blackish brown. Valves slightly beaked; lateral area separated from the central area by a prominent, raised row of beads. Central areas with many coarse, wavy, longitudinal riblets, which are sometimes pitted between. Lateral areas coarsely granu- lated or wrinkled. Posterior valve small, with a deep slit on each side and a broad, deep notch at the very posterior end. Girdle fairly wide, generally notched at the posterior end and clothed with curly, strap-like brown hairs between which are much smaller, glassy white hairs or spicules. Interior of valves greenish white. Anterior valve granulated and with 8 to 9 coarse, raised rays of beads. A common intertidal species. The subspecies ivosnes- senski Middendorff (Alaska to Puget Sound) is supposed to be without the tiny white spicules in the girdle. Mopalia muscosa Gould Mossy Mopalia Alaska to Lower California. I to 2 inches in length, oblong to oval. Very similar to M. ciliata, but differing in having a very shallow and small notch at the very posterior end. Color usually a dull-brown, blackish olive or grayish. Interior of valves blue-green, rarely stained with pinkish. Girdle with stiff hairs resem- bling a fringe of moss. The following species have been considered by some workers as varieties of 7miscosa, and perhaps with some justification: lignosa Gould, hindsi Reeve, acuta Carpenter, the latter having also been named plumosa and fissa by Carpenter. A common intertidal species. Mopalia lignosa Gould Woody Mopalia Alaska to Lower California. I to 2^4 inches in length, oblong. Color a grayish green or blackish green, rarely with whitish cream and brown, feathery markings. The sculp- turing on the valves is very delicate and may consist only of numerous small pittings near the center. Concentric growth lines in smoother specimens are quite easily seen. Radial ribs absent on the end valves. Girdle solid or macu-