Plicacesta, VOKES, 1963

Hickman, Carole S., 2023, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part II: The pteriomorphs, PaleoBios 40 (5), pp. 1-51 : 41

PLICACESTA VOKES, 1963

Type species — By original designation, Lima smithii G. B. Sowerby III (1888) . Holocene, Japan .

Discussion — Plicacesta is usually treated as a subgenus of Acesta , along with the extinct Upper Cretaceous Costellacesta Kauffman (1964) and extinct Eocene Antarcticesta Stilwell and Gaździcki (1998) . It is treated here as a distinct genus that includes similarly large-shelled limids with prominent sculpture of well-developed radial ribs and interspaces over the entire shell and most strongly developed on the central portion. The hingeplate is thick, with a strongly oblique (opisthocline) resilifer with curved margins. As noted by E.J. Moore (1987, p. C15) the Eastern Pacific fossil species assigned to Plicacesta have considerably thicker shells than the living species, and it is possible this is a paraphyletic group. These thick-shelled forms first appear in the Paleogene of central and southern California. A specimen from the Keasey-equivalent Gries Ranch Formation provides new documentation of both exterior sculpture and the interior hinge plate and strongly oblique resilifer.

Stratigraphic range —Paleocene–Holocene.