Page:American Seashells (1954).djvu/404

322 Ischnochiton regularis Carpenter Regular Chiton Southern CaHfornia. I to i^ inches in length, oblong, appears smooth to the naked eye. Color an even slate-blue or uniform olive-blue. Valves slightly carinate. Central areas with very fine, longitudinal threads. Lateral areas slightly raised and with radial threads. Interior of valves gray-blue. Girdle with very tiny, closely packed, low, round scales. Moderately common between tides. Subgenus Lepidopleuroides Thiele 1928 Ischnochiton albus Linne White Northern Chiton Arctic Seas to Massachusetts. Europe. Arctic Seas to off San Diego, California. About Yz inch in length, oblong, moderately elevated. Upper surfaces smoothish except for irregular, concentric growth ridges and a microscopic, sandpapery effect. Color whitish, cream, light-orange or rarely marked with brown. Interior of valves white. Posterior valve with 12 to 13 weak slits. 17 to 19 gill lamellae on each side, beginning about halfway alongside the foot. Girdle sandpapery, with tiny, closely packed, gravelly scales. Com- mon from shore to several fathoms in cold water. Distinguished from ruber by the anterior slope of the anterior valve which is straight to slightly con- cave in albus, but convex in ruber. Ischnochiton ruber Linne Red Northern Chiton Arctic Seas to Connecticut. Europe. Alaska to Monterey, California. V2 to I inch in length, oblong, moderately elevated and with the valves rather rounded. Upper surfaces smooth except for growth wrinkles. Colored a light-tan over which is a heavy suffusion of orange-red marblings, or en- tirely suffused with red. Interior of valves bright pink. Posterior valve with 7 to 1 1 slits. Girdle reddish brown with weak maculations; covered with minute, elongate scales which do not overlap each other. 15 to 18 gill la- mellae, similar to those in albus. Common from i to 80 fathoms. Do not confuse with Tonicella marmorea Fabr. whose girdle is naked. Subgenus Lepidozona Pilsbry 1892 Ischnochiton mertensi Middendorff Mertcn's Chiton Aleutians to Lower California,