Shell. Low profile, thick, large (up to 100 mm); apex positioned in the anterior quarter of shell. Anterior slope straight to concave; posterior and lateral slopes convex. Sculpture of slightly raised squarish radial ribs. Shell sometimes smooth. Central area commonly eroded by fungal infections. Edges slightly crenulate. Shell brown with white markings, forming rays or reticulate pattern; eroded areas dull white. Interior margin black; intermediate area brown to black; central area white with irregular brown markings. Myostracum prominent. Length, 20-100 mm.
Animal. Solid black markings on sides of foot and dorsal surface of head.

Radula. First lateral teeth closely set on anterior edge of ribbon segment, blunt distally. Second lateral teeth posterior to first lateral teeth, broad, medial edges straight, lateral edges convex, blunt distally. Third lateral teeth lateral to second lateral teeth; wedge-shaped, reduced. Uncini large. First lateral plates square; second lateral plates irregular, separated from third lateral plates by partial suture. Third lateral plates biformed, posterior edge rounded, lateral edge hook-shaped. Ventral plates slightly compressed, subrectangular, with notches at anterolateral corners.

This is the largest limpet in North American waters and the only species in genus Lottia. It differs from other limpet genera in our waters in possessing a ring of small gill filaments under the mantle. The shell is frequently polished and sold as jewelry or souvenirs, and is commonly found in Indian food middens. The white spots are sometimes obscure in large specimens and more obvious in small. The common name stems from the owl-like outline of the interior scar.[Rehder]

Neah Bay, Washington (48°30TC) to Bahia San Bartolome, Baja California, Mexico (27°30'N) (McLean, 1966:50). Middle intertidal; exposed, high energy areas.. San Francisco Bay: not reported.
Lottia gigantea has not been reported in San Francisco Bay, although it was reported from the area by Packard (1918) who erroneously cited Carpenter as the author. Lottia gigantea is an intertidal, territorial, exposed coast species that is suspected of being present along the northern and southern shores of the Golden Gate, as this habitat appears favorable for the species. Lottia scabra is a common epizooic on Lottia on the outer coast.