Chesapecten covepointensis Ward, 1992
WARD, L. W. 1992. Molluscan bioestratigraphy of the Miocene, Middle Atlantic Coastal Plain of North America. Memoirs of theVirginia Museum of Natural History, 2: 1-159, pls. 1-26. [p. 70, pl. 11, figs. 2, 3, 6]
1992 Chesapecten (Chesapecten) covepointensis Ward, 1992
L. W. Ward, 1992, plate 11.
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«Diagnosis.─ Valves medium in size, sub-orbicular, with small auricles, a deep byssal notch, and 17 very scaly ribs radiating from a low beak.
Description.─ Valves medium-sized for the genus, nearly orbicular in outline. Auricles small for the size of the disk, reflecting the shorter hinge. Ribs averaging 17, with numerous raised scales both on the ribs and in the interspaces. Three rows of scales on each rib and their interspaces in adult forms. Left valve only slightly convex, right valve even less convex. Byssal fasciole on the right valve moderately deep with two small teeth on the active area of the ctenolium on the holotype (USNM 405199). Right valve with scales better developed and low umbonal area. Beak prominent. Valves very thin with ribs clearly reflected on interior of shell except in umbonal region above the muscle scar. Muscle scar weakly impressed and somewhat posterior to the midline. Discussion.─ This species clearly resembles both Chesapecten nefrens, a stratigraphically lower form, and C. santamaria, a stratigraphically higher form. The species retains the extremely scaly nature of C. nefrens while acquiring the rounded disk outline and smaller auricles of C. santmaria. The taxon also has coarser scales than C. santamaria. For these reasons C. covepointensis appears to be a true intermediate form in an evolutionary continuum. In its type area, Little Cove Point, Calvert County, Md., it is a common form but never abundant. Many of the valves there are water-wom and were deposited in a shallow inner bay. Type information.─ Holotype: USNM 405199. Type locality: Below Little Cove Point, westem shore of the Chesapeake Bay, Calvert County, Md. (locality 15). Figured specimens.─ Plate 11, figure 2: Holotype, USNM 405199 from the type locality; Plate 11, figure 3: A right valve (USNM 405201) from the same locality; Plate 11, figure 6: Paratype (USNM 405200), a left valve from the same locality. Stratigraphic and geographic range. ─ St. Marys Formation, Little Cove Point beds (lower upper Miocene) in Maryland.» LAUCK W. WARD, 1992
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