California Horn Shell, Cerithideopsis californica  

California Horn Shell, Cerithideopsis californica. Shell collected in the greater Cabo San Lucas area, Baja California Sur, May 2017. Size: 3.9 cm (1.5 inches) x 1.6 cm (0.6 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

The California Horn Shell, Cerithideopsis californica (Haldeman, 1840), is a member gastropod mollusk that is a member of the Potamididae Family of Horns. The shell have a narrow cone-shaped profile with about ten, slightly rounded whorls and a round aperture. The exterior of the shell is sculpted by weak length-wise and spiral ridges. Most specimens will display one or more short varices. The operculum is corneous (made of horn-like material). The exterior of the shells are brown in color. California Horn Shells reach a maximum of 4.4 cm (1.7 inches) in length and 1.8 cm (0.7 inches).

California Horns are found in large aggregations shallow water environments on sandy mud substrate in back bay and estuaries from the intertidal zone to depths up to 5 m (15 feet). They range from Central California to San Ignacio Lagoon, Baja California Sur. The California Horn Shell is very similar to the Mazatlán Horn Shell, Certhidea mazatlanica (white varices and aperture lips), that is found in the Sea of Cortez and south to Panama.

Synonyms include Certhidea albodonosa, Certhidea californica, Certhidea mazatlanica, Certhidea sacrata, Certhidea valida, Certhium californicum, and Certhium sacratum.