REVIEW OF THE BIVALVE GENUS PLICATULA FROM CRETACEOUS AND LOWER CENOZOIC STRATA OF CALIFORNIA AND BAJA-CALIFORNIA

The Cretaceous and early Cenozoic species of the shallow-marine, warm- water bivalve Plicatula from California (United States) and Baja Calif ornia (Mexico) are reviewed, and three new species are named. All of t hese species are representatives of Plicatula and not of the closely r elated taxon Harpax, which is associated with high-latitude and cool-w ater regions. The earliest-known Cretaceous species of Plicatula from the study area is P. variata Gabb, 1864, from Lower Cretaceous (Hauter ivian Stage) strata in northern California, and our studies show it to be conspecific with Plicatula onoensis Anderson, 1958. Plicatula alli soni new species is from Lower Cretaceous (Albian Stage) strata in Baj a California, Mexico. Plicatula modjeskaensis new species is from Uppe r Cretaceous (Turonian Stage) strata in the Santa Ana Mountains, south ern California. A possible new species from the same strata is also me ntioned. A poorly preserved specimen of Plicatula? sp. is known from U pper Cretaceous (upper Campanian to lower Maastrichtian) strata in nor thern California. The only Paleocene species of Plicatula from the stu dy area is P. ostreiformis Stanton, 1896, from lower Paleocene strata of Lake County, northern California, and our studies show it to be con specific with Ostrea buwaldana Dickerson, 1914. The only previously de scribed Eocene species of Plicatula from the study area is P. juncalen sis Squires, 1987, from lower middle Eocene (''Capay Stage'') strata o f Los Angeles County, southern California. Plicatula surensis new spec ies is from middle lower Eocene (''Capay Stage'') strata in Baja Calif ornia Sur, Mexico. In addition, there is a Plicatula? sp. from Eocene strata of Baja California Sur, Mexico. Although Plicatula is of uncomm on occurrence north of Baja California, its thermophilic trait makes i t useful in recognizing periods of warm climate.