Shell. Medium profile; apex positioned in the anterior third of shell. All slopes straight to slightly convex. Sculpture of concentric growth lines. Aperture oval. Color gray to brown, some specimens with white tessellations and / or white radial markings at margins. Apex erodes to brown, adjacent areas may erode to white. Interior margin broad, dark; intermediate area blue-white suffused with brown; interior stain brown. Length, 10-30 mm.

Animal. Lacks pigmentation.

Radula. First and lateral teeth closely set at anterior edge of ribbon segment, pointed distally; second lateral teeth posterior of first lateral teeth, broad, elongate, pointed distally. Third lateral teeth lateral of second lateral teeth, pointed distally, reduced. Lacks marginal teeth. First and second lateral plates square; third lateral plates lobate, lateral of second lateral plates, and separated from second lateral plates by partial suture. Ventral plates subrectangular with broad, flat anterior process.

Middle to low intertidal, on bare rocks embedded in sand or mud. Also found in aggregations on rock outcroppings. Shumagin Islands, Alaska (55°N, 160° W) to Punta Pequeha, Baja California, Mexico (26°14rN). San Francisco Bay: San Francisco County—Land's End, Fort Point, St. Francis Yacht Club Breakwater, Aquatic Park, Alcatraz Island, Angel Island; Marin County—Peninsula Point, Cone Rock; Contra Costa County—Castro Rocks; Alameda County—Fleming Point.