Chesapecten monicae Ward, 1992
WARD, L. W. 1992. Molluscan bioestratigraphy of the Miocene, Middle Atlantic Coastal Plain of North America. Virginia Museum of Natural History, Memoir number 2: 1-159, pls. 1-26. [p. 71, pl. 14, figs. 1-6]
1992 Chesapecten (Chesapecten) monicae Ward, 1992
L. W. Ward, 1992, plate 14.
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«Diagnosis. ─ Small, orbicular valves with 10-13 very finely striated ribs. Scales very small to obsolete.
Description. ─ Valve small, thin wirh 10-13 ribs. Ribs somewhar distanr, flattened and exhibiring only a trace of scaling patterns to the unaided eye. Very fine striations radiating from the low umbones are evident on the ribs and their interspaces under moderate magnification. Ribs developing three lines of very subdued scales. Ribs low, flat and wide medially, becoming thin anteriorly and posteriorly. Auricles with smooth striae radiating from beak. Valve moderately convex. Interiorly, ribs flat and sharply defined to correspond with exterior sculpture. Ribs obscured in beak area. Ligamental pit small and triangular. Measurements (in millimeters).─
Discussion. ─ This taxon is based on four individuals. Because of their small size they are easily confused with the young of Chesapecten nefrens. They differ in having fewer ribs and more subdued scaling patterns. The young of C. nefrens have, at a similar size, fully defined rows of scabrous lirae on the auricles and the ribs. It is possible that C. monicae represents a small offshoot from the Chesapecten lineage in the upper middle Miocene. The species is named in honor of Monica Genadio, who worked for the U.S. Geological Survey in 1983-1984.
Type information. ─ Holotype: USNM 405204. Type locality: Boston Cliffs Member of the Choptank Formation, just below Flag Pond and just north of the Baltimore Gas and Electric Power Plant, Calvert County, Md. (locality 17). Figured specimens. ─ Plate 14, figure 1: holotype (USNM 405704); Plate 14, figures 2, 5: paratype, USNM 405205; Plate 14, ftgures 3, 6: Paratype, USNM 405206; Plate 14, figure 4: paratype, USNM 405207. Stratigraphic and geographic range. ─ Choptank Formation, Boston Cliffs Member (upper middle Miocene) in Maryland. Known only from the type locality in Calvert County, Md.» LAUCK W. WARD, 1992
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