Scutellastra mexicana
Scutellastra mexicana is a species of true limpet, a marine gastropod mollusk in the family Patellidae. It  is the largest known limpet in the world. This species has been harvested since pre-Hispanic times. In Mexico, it was harvested heavily in the 1970s and 1980s, leading to closing of the fishery in 1988. However, the harvest has continued, and it is feared that Scutellastra mexicana  is in danger of extinction. Description
Scutellastra mexicana can reach  in length. Distribution and habitat
Scutellastra mexicana occurs along the American Pacific coast from Mexico to Peru. It inhabits lower intertidal and subtidal rocky areas exposed to heavy swells. References

Further reading
 

Patellidae
Molluscs of the Pacific Ocean
Gastropods described in 1829
Taxa named by William Broderip
Taxa named by George Brettingham Sowerby I