Rebeccapecten Ward, 1992
WARD, L. W. 1992. Molluscan bioestratigraphy of the Miocene, middle Atlantic Coastal Plain of North America. Memoirs of the Virginia Museum of Natural History, 2: 1-159, pls. 1-26. [p. 64]
«Genus Rebeccapecten, new genus
Diagnosis.— Valves higher than long with a variable number of large, scaly, bifurcating ribs. Shell thick for its size with a deep byssal notch. Right valve deep, left valve nearly flat to slightly concave.
Description.— Disk noticeably higher than long with a variable number (average 10-12) of scaly ribs radiating from a prominent, sharp beak. Ribs variable in size and number. Right valve of young specimens have 10-12 entire ribs with small scales in the very young portion of the shell (up to 7 mm). After that stage the ribs develop a strong medial sulcus as the ribs bifurcate and become more scaly. At an average height of 28 mm the ribs again bifurcate as rib prominence diminishes with each division. Scales become wide, thin plates that stand at nearly right angles to the shell. The right valve is deeply convex with prominent auricles, a deep byssal notch, and a well-defined ctenolium. Left valve moderately convex in the early stages, becoming flat to moderately concave in the adult. I-eft valve with four or five prominent ribs, the others very small. Bifurcation of the ribs and scaling pattems of the left valve as in the right. Both valves thick for their size. Interiorly the right valve is deep with a rounded ventral margin. Pallial line deep and finely crenulated marking, the distal margin of thick shell material. Muscle scar somewhat posterior, deeply impressed, and nearly circular. Ribbing is reflected only in the distal half of the shelf between the shell margin and the pallial line. Interiorly the left valve is shallow and its ventral margin is angular to match the four or five primary ribs. Left valve in other respects is similar to right valve.
Discussion.— The genus Rebeccapecten founded on the species Pecten trentensis, named by G. D. Hanis in 1919 in a short paper on Eocene mollusks. Even at that time Harris doubted its Eocene age but provisionally considered it as such. Rebeccapecten trentensis is now considered to be Oligocene in age (Ward et al., 1978). Rebeccapecten trentensis occurs abundandy in the lower calcareous portion of the River Bend Formation in North Carolina, but also occurs, sparingly, in the upper, arenaceous, mold-and-cast limestone portion of that unit. It is found, but not commonly, high in the upper River Bend in the mold-and-cast limestone, at the Martin Marietta Quarry at Belgrade, Onslow County, N.C. (locality 29, USGS locality 26570). Another species of the genus, Rebeccapecten berryae, n. sp. succeeds R. trentensis in the Haywood Landing Member of the Belgrade Formation. Rebeccapecten berryae is a much larger form. The genus Nanaochlamys Hatai and Masuda, 1953 resembles Rebeccapecten, but the Japanese taxon is much larger in size and has fewer and larger ribs, which do not bifurcate until a late growth stage.
Etymology.— The genus is named for Rebecca Berry, who worked for the U.S. Geological Survey in 1984-1985.
Type information.— Type species: Pecten trentensis Harris is selected as the type species of Rebeccapecten. The specimen, PRI 1407, of the Hanis collection is designated the lectotype of P. trentensis. Paratype, herein designated, PRI 1408. Type locality: "Found in the light, marly bed, right bank of Trent river, near the water's edge, about six miles below Pollocksville, N. C., in the so-called Trent formation" (Harris, 1919, p. 15).
Stratigraphic and geographic range.— River Bend Formation (upper Oligocene) in North Carolina. Haywood Landing Member of the Belgrade Formation (upper Oligocene and lower Miocene) and the basal Pungo River Formation (lower Miocene) in North Carolina.»
LAUCK W. WARD, 1992
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Rebeccapecten berryae Ward, new species, holotype; L. W. Ward, 1992, Molluscan bioestratigraphy of the Miocene, middle Atlantic Coastal Plain of North America, plate 24, figure 1.
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