Medium to high profile; apex positioned in anterior third of shell. Anterior slope concave, apex may overhang the anterior edge of the shell; posterior and lateral slopes convex. Sculpture of radial ribs stronger on the posterior surface than on the anterior surface; posterior shell edge sometimes crenulate from the presence of these ribs, otherwise rounded. Aperture anteriorly narrowed. Color grayish-green to black with fine tessellations, brown to black with white chevron markings or blotches, or combinations of both. Anterior margin typically bears several white radial markings. Interior margin dark, with or without white markings depending on the external shell pattern; intermediate area white to blue-white; interior stain brown, irregular. Length, 10-25 mm.
Animal. Lacks pigmentation, white; lacks oral lappets. Radula. First lateral teeth closely set at anterior edge of ribbon segments, pointed distally. Second lateral teeth posterior to first lateral teeth, pointed distally, cusps approximately at median of radular ribbon units. Third lateral teeth lateral to second lateral teeth, pointed distally, reduced. Uncini large. First lateral plates ovoid; second lateral plates irregular, medial edge convex, tapering to point, separated from third lateral plates by long, partial suture. Third lateral plates biformed, posterior edge rounded, lateral edge hook-shaped. Ventral plates subrectangular, elongate, anteriorly rounded forming anterior process. Habitat: High intertidal; solitary or forming aggregations. A situs form occurs on the tergal and scutal plates of the stalked barnacle Pollicipes polymerus Sowerby, 1834.

Lottia digitalis is a highly variable species and can be confused with Lottia pelta or Lottia scabra . Lottia digitalis is readily distinguished from L. scabra by several characters. The sides of the foot and the head area of L. scabra are marked with black markings. Lottia digitalis is unpigmented, the animal being entirely white. The area inside the myostracum of L. scabra is covered by a callus; L. digitalis lacks a callus. The interspaces between the primary ribs of L. scabra typically contain small indentations along the interior margin that are marked with brown or black. Lottia digitalis lacks these indentations; instead the interspaces are smooth. Lastly, the interior shell layers of the 2 species differ markedly. In L. scabra the interior margin consists of a single wide layer, typically not colored except for the interspace indentations. This layer is then followed by another whitish layer that extends to the myostracum. The transition between these 2 layers is gradual. In L. digitalis the outermost layer is thin, dark, and barely visible around the shell aperture. This layer is followed by a wider layer that is typically colored like the first. A sharp demarcation exists between the second and next inner layer. This third layer corresponds to the intermediate area and accordingly is not colored.
Differentiation between L. digitalis and L. pelta is more difficult. Both species have unpigmented, white bodies, and the shell structure of both is identical. However, the shell of L. pelta has a more subcentral apex rather than the strongly anterior apex of L. digitalis. The anterior slope of L. pelta is straight to convex rather than concave as in L. digitalis. The radula of L. digitalis is easily distinguished from other species by the basal tapering of the second lateral teeth, a character not observed in other species of Lottia found along the California coast.

Southwestern Alaska to Cabo San Lucas, Baja California, Mexico (23°N). San Francisco Bay: San Francisco County—Fort Point, St. Francis Yacht Club Breakwater, Black Point, Aquatic Park, Alcatraz Island, Angel Island, Yerba Buena Island; Marin County—Fort Baker, Sausalito Breakwater, Cone Rock, Tiburon Point, Peninsula Point, Yellow Bluff; Contra Costa County—Castro Rocks; Alameda County—Fleming Point, Berkeley Marina, Emeryville, Alameda Naval Air Station Breakwater; San Mateo County—Coyote Point, western terminus San Mateo Bridge.