The Pacific Spiny Cockle, Dallocardia quadragenaria (Conrad, 1837), is a bivalve mollusk that is a member of the  Cardiidae Family of Cockles and True Cockles. This shell has many common names, including: Giant Pacific Cockle, Spiny Prickly Cockle, and Spiny Cockle (Pacific). The shell is very inflated with a rounded quadrilateral profile. The exterior has approximately 40 radiating ribs, which extend to the margins, causing the margins to be scalloped. The ribs are sculpted with small, sharp, tubercles. These shells are yellowish to brownish in color. The inside is white. Pacific Spiny Cockles are large bivalves, reaching a maximum of 13.0 cm (5 inches) in length and 12 cm (4.7 inches) in height.

The Pacific Spiny Cockle is found within bays and on sandy substrates offshore. They are found intertidally, and to a depths up to 40 m (135 feet). They are suspension feeders that filter plankton and fine detritus from the surrounding water. In Mexico, they are found along the West Coast of the Baja Peninsula, from Tijuana south to Magdalena Bay, and perhaps to the Cape region or Baja California Sur. They have not been documented from the Gulf of California.

Synonyms include Cardium arenatum, Cardium luteolabrum, Cardium quadragenarium, and Trachycardium quadrgenarium.