1⁄2 inch in maximum diameter, very narrow, 3 times as long as wide. Sides straight with brown vertical stripes on a whitish background. Smoothish. This species is found on the broad-leaved eel-grass of the estuaries. Abundant in certain localities, such as Mission Bay.
Plate 18zz
Alaska to San Diego, California.
1 to 11⁄4 inches in maximum diameter, oblong with a rather high apex. Sides compressed. Lower edge curved so that the shell rocks back and forth if put on a flat surface. Exterior dull, light-brown. Interior whitish with faint brown stain in the center and with a narrow, solid border of brown. Inhabits the stems or holdfasts of large seaweeds. Moderately common.
Plate 18z
Alaska to Lower California.
1⁄2 to 3⁄4 inch in maximum diameter, narrowly elliptical, with a high apex, and colored a uniform, greasy light-brown. Abundant on the stalks or hold-fasts of the large seaweeds, such as Egregia.
Vancouver, B.C., to Lower California.
1⁄4 inch in maximum diameter, very fragile, translucent-brown, 3 or 4 times as long as wide. Sides straight with fine, raised radial threads. Abundant on the narrow-leaved eel-grass of the open coast.
Atlantic Coast Species
Arctic Seas to Long Island Sound, New York.
1 to 11⁄2 inches in maximum diameter, oval in outline, moderately high with the apex nearly at the center of the shell. Smoothish except for a few coarse growth lines and numerous, very fine axial threads. Interior bluish white with a dark- to light-brown center and with short, radial brown bars at the edge. Exterior dull cream-gray with irregular axial bars and streaks of brown. A common littoral species in New England. Formerly referred to as A. tessulata Müller. The form alveus Conrad is a thin, elongate, heavily mottled ecological variant which lives on eel-grass.
