The horn shark (Heterodontus francisci) is a species of bullhead shark, in the family Heterodontidae. It is endemic to the coastal waters off the western coast of North America, from California to the Gulf of California. Young sharks are segregated spatially from the adults, with the former preferring deeper sandy flats and the latter preferring shallower rocky reefs or algal beds. A small species typically measuring in length, the horn shark can be recognized by a short, blunt head with ridges over its eyes, two high dorsal fins with large spines, and a brown or gray coloration with many small dark spots. Slow-moving, generally solitary predators, horn sharks hunt at night inside small home ranges and retreat to a favored shelter during the day. Their daily activity cycles are controlled by environmental light levels. Adult sharks prey mainly on hard-shelled molluscs, echinoderms, and crustaceans, which they crush between powerful jaws and molar-like teeth, while also feeding opportunistically on a wide variety of other invertebrates and small bony fishes. Juveniles prefer softer-bodied prey such as polychaete worms and sea anemones. The shark extracts its prey from the substrate using suction and, if necessary, levering motions with its body. Reproduction is oviparous, with females laying up to 24 eggs from February to April. After laying, the female picks up the auger-shaped egg cases and wedges them into crevices to protect them from predators. Horn sharks are harmless unless harassed, and are readily maintained in captivity. They are not targeted by either commercial or recreational fisheries, though small numbers are caught as bycatch. In Mexico this species is used for food and fishmeal, and in California its spines are made into jewelry. The International Union for Conservation of Nature (IUCN) does not yet have enough information to determine the horn shark's conservation status. It faces few threats off the coast of the United States. Taxonomy The French biologist Charles Frédéric Girard published the first scientific description of the horn shark under the name Cestracion francisci in 1855, in the Proceedings of the Academy of Natural Sciences of Philadelphia. This species was later placed in the genus Gyropleurodus, which was eventually synonymized with the genus Heterodontus. The specific epithet francisci is a reference to San Francisco, although the range of the horn shark does not extend that far north. The type specimen from Monterey Bay has since been lost. The scientific name for this