NEW EARLY EOCENE SPECIES OF ARCA SS (MOLLUSCA, BIVALVIA) FROM SOUTHERN CALIFORNIA

Two new species of the warm-water marine bivalve Arca s.s. are reported from the early Eocene of Ventura County, southern California. They represent the earliest species of Arca s.s. known from the Pacific coast of North America. Arca (Arca) filewiczi sp. nov. is from the early early Eocene part of the "Meganos Stage" in the upper Santa Susana Formation, north side of Simi Valley, southern California. Arca (Arca) givensi sp. nov., a previously unnamed species from the middle early Eocene "Capay Stage," part of the Juncal Formation, Pine Mountain area, southern California, is now named and described.