ately larger apical hole which is sharp at its top edge and which is nearer the center of the shell. The ends of the shell are slightly turned up and the sides are slightly concave. Sculpture of about 2 dozen heavily scaled, radial ribs and numerous, fine, thread-like concentric ridges. Color whitish with weak mauve or brown discoloring. Commonly dredged off southeastern Florida, from 6 to 60 fathoms.
Plate 18e
Bodega Bay, California, to Nicaragua.
3⁄4 to 1 inch in length, narrower at the anterior end, quite flat. Base flat and usually with strong crenulations on the under edge. Sides slightly concave. Apical hole narrowly elongate, slightly nearer the anterior end, about 1⁄5 the length of the shell and with flat inner sides. Sculpture coarsely cancellate with the radial ribs stronger and often scaled. Color dark-gray with irregular, darker, radial color-rays. Rather rare under rocks in the low tide zone.
Genus Megathura Pilsbry 1890
Plate 18a
Monterey, California, to Cedros Island, Mexico.
21⁄2 to 4 inches in length, 1⁄5 as high. Apical hole large, with rounded sides, 1⁄6 the length of the shell, and bordered externally by a white margin. Interior glossy-white. Basal edge finely crenulate. Exterior finely beaded and light mauve-brown. Animal much larger than the shell, with a massive, yellow foot and a black or brown mantle that nearly covers the entire shell. Common in many low-tide, rocky areas, such as breakwaters.
Genus Megatebennus Pilsbry 1890
Plate 18d
Alaska to Tres Marias Islands, Mexico.
3⁄4 to 5⁄8 inch in length, low, with ends turned slightly up. Apical hole elongate-oval, located at the center of the shell and about 1⁄3 the length of the shell. Numerous radial and concentric threads give a fine cancellate sculpturing. Color dark-gray to light-brown with a wide, darker ray on each side of the hole, and occasionally at each end. Interior white to grayish. Animal several times as large as the shell, variable in color—red, yellow or white. Common under stones at low tide.
