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356 Genus Botula Morch 1853 Subgenus Adula H. and A. Adams 1857 Botula falcata Gould Falcate Date Mussel Plate 29k Coos Bay, Oregon, to Lower California. 2 to 4 inches in length, very elongate, slightly curved. Beaks rounded and about one-eighth the length from the anterior end; a strongly marked angle occurs from the beaks to the base of the posterior extremity; numerous vertical, wavy ribs over all the shell. Color a shiny chestnut-brown. Com- mon. Botula californiensis Philippi Californian Date Mussel Plate 29h I to 1^4 inches in length, elongate, curved and smooth, except for a velvety, hair-like covering over the posterior end. Shiny, chocolate-brown in color. Moderately common. Genus Lioberus Dall 1898 Lioberus castaneus Say Say's Chestnut Mussel Both sides of Florida and the West Indies. % inch in length, oval-elongate, well-inflated and thin-shelled. Exterior chestnut- to dark-brown, the anterior half glossy, the posterior half dull and commonly with a fine grayish matting of periostracum. Interior bluish white and with an irregular surface. Hinge simple with a slight swelling or pad under the beaks. Moderately common in shallow water. Botula fusca Gmelin from North Carolina to southeast Florida (rare) and the West Indies (common) is similar, but distinguished by its longer, hooked or arcuate shape, by the thick, concentric ridges on the outside, by the more anteriorly placed beaks, and by the tiny, vertical threads on the hinge just posterior to the ligament. Attached in clusters to wood and rocks. Genus Lithophaga Roding 1798 Lithophaga nigra Orbigny Black Date Mussel Plate 2 8in Southeast Florida and the West Indies. I to 2 inches in length, elongate and cylindrical. Black-brown outside and an iridescent bluish white inside. Anterior lower third of each valve