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316 lated with browns and yellows. Strap-like, brown hairs not numerous. In- terior of valves greenish white to white. Moderately common. Mopalia hindsi Reeve Hinds' Mopalia Alaska to the Gulf of California. 2 to 3 inches in length, oblong, flattened and resembhng M. ciliata Sowerby, but generally smoother. Girdle brown, rather thin and fairly wide, and almost naked except for a few short hairs. Interior of valves white with short crimson rays under the beaks. Moderately common. Genus Placiphorella Dall 1878 Placiphorella velata Pilsbry Veiled Pacific Chiton Figure 66a Monterey, California, to Lower California. 1 to 2 inches in length, readily recognized by its flat, oval shape and wide girdle which is very broad in front. There are a few hairs on the girdle which, if viewed under a lens, will be seen to be covered by a coat of diamond-shaped scales. Girdle reddish yellow. Valves colored a dull olivaceous brown with streaks of buff, blue, pink or chestnut. Interior of valves white with a slight bluish tint. Posterior valve with i to 2 slits and with very large sutural plates. Fairly common intertidally. Genus Katharina Gray 1847 Katharina tunicata Wood Black Katy Chiton Figure 66b Aleutian Islands to southern California. 2 to 3 inches in length, oblong and elevated. Characterized by its shiny, naked, black girdle which covers % of each gray valve. Valves usually eroded. Anterior valve densely punctate. Interior of valves white. Foot salmon to reddish. Very common between tides, especially in the north. Genus Syimnetrogephyriis Middendorff 1847 (Amicula Gray 1847, not 1842) Symmetrogephyrus vestitus Broderip and Sowerby Concealed Arctic Chiton Figure 66c Arctic Seas to Massachusetts Bay. Arctic Seas to the Aleutian Islands. I to 2 inches in length, oval, rather elevated. Valves covered with a thin, smooth, brown girdle except for a small, heart-shaped exposure at the