Plicacesta bela

• Main Author: Hickman, Carole S.
• Format: Other/Unknown Material
• Language: unknown
• Published: Zenodo 2023
• Subjects: Biodiversity; Taxonomy; Animalia; Mollusca; Bivalvia; Limida; Limidae; Plicacesta; Plicacesta bela; Antarc*; Antarctic
• Online Access: https://doi.org/10.5281/zenodo.11505157; http://treatment.plazi.org/id/C23987DDFFD22910FC22F9FFEEFEBBAC

PLICACESTA BELA (DICKERSON, 1917) FIGS. 28A–C Lima bela Dickerson (1917). pp. 172–173; pl. 29, fig. 11. Lima (Radula) oakvillensis Clark (1925). p. 84; pl. 14, figs. 1, 3. Lima bela Dickerson, Effinger (1938). pp. 368–369. Lima bela Dickerson, Weaver (1943). pp. 97–98; pl. 21, fig. 3. Lima oakvillensis Clark, Weaver (1943). p. 98; pl. 21, fig. 1; pl. 22, fig. 7. Acesta (Plicacesta) oakvillensis Clark, E.J. Moore (1984a). pp. 27–28; figs 118, 132, 134. Not Acesta cf. A. oakvillensis Clark, Addicott (1976a). p. 441; fig. 6ac. Discussion —The resilifer is clearly posterior to the beak. The posterior ear is well-developed on the rounded posterior dorsal margin. The anterior dorsal margin is straight, anterior to the beaks, and lacking evidence of a discrete ear. The radial ribs are strongly developed, with flat-bottomed interspaces that are wider than the radial ribs on the central portion of the shell. The ribs become scabrous at intersections with concentric growth increments. Shells are more similar in shape, ornamentation, and cardinal area to those of the Japanese type species of Plicacesta than to other species that have been assigned to the genus. The robust sculpture is more typical of the Cretaceous (Maestrichtian) species of Costellacesta illustrated by Kauffman (1964), although interspaces lack the fine secondary radial threads characteristic of the geologically older genus. The monotypic and endemic Antarctic genus Antarcticesta is distinguished by its thin shell and sculpture of very broad, scaly, and widelyspaced radial ribs. Recognition of four distinct genus group taxa has considerable morphological support as a working hypothesis. Dickerson described Lima bela from a small, left valve. Specimens of large adults collected subsequently from the type locality (Fig. 28A, B) cannot be distiguished from Plicacesta oakvillensis , described by Clark (1925) from the coeval beds in the lower part of the Lincoln Creek Formation at the Oakville Quarry (Fig. C). Unfortunately, both Dickerson and Clark confused ...