Placopecten princepoides (Emmons, 1858)
EMMONS, E. 1858. Paleontology. In Agriculture of the eastern counties; together with descriptions of the fossils of the Marl Beds, pp. 193-313, figs. 18-256. North Carolina Geological Survey. Raleigh, North Carolina. [p. 280, fig. 198]
1858 Pecten princepoides Emmons, 1858
1936 Pecten (Chlamys) clintonius rappahannockensis Mansfield, 1936
1936 Pecten (Chlamys) clintonius rappahannockensis Mansfield, 1936
E. Emmons, 1858, figure 198.
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«Shell large, rather thick, compresed, sub-inequilateral, radiating striae coarse and very numerous; transversely marked by lines of growth, giving the surface a wrinkled appearance; ears unequal; buccal ear sinuate, radiating striae numerous, inside smooth, striae obsolete; fig. reduced.
This is a large species of pecten, is closely allied to the P. princeps of the English crag. It is common in the miocene marl on the Meherrin river, at Murfreesboro'. It is five inches long, and five and a quarter wide. It is readily distinguished by the absence of ribs proper, and the presence of coarse radiating striae, which have intermediate ones, which do not reach the hinge or umbo; many of the striae, however, fork or divide.» EBENEZER EMMONS, 1858
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Discussion.— Placopecten princepoides (Emmons) has long been lost in synonomies of Placopecten clintonius (Say) (for example: Gardner, 1943 [1944], p. 37; Dall, 1898b, p. 726). I have examined Emmons' type material, now at the Paleontological Research Institution (recently acquired from Williams College), and have concluded that Emmons was describing, however nebulously, the Cobham Bay species later named by Mansfield Pecten clintonius rappahonnockensis. A trip by the author to the type area indicated by Emmons confirmed that the species is present in large numbers in the Cobham Bay Member of the Eastover Formation in outcrops along the Meherrin River just above Murfreesboro, N.C. The Sunken Meadow Member of the Yorktown Formation (Zone 1 of Mansfield, 1943 [1944]) is also present and contains many specimens of Placopecten clintonius (Say). The type material of Emmons, however, contains only specimens from the Cobham Bay Member.
Placopecten princepoides differs from P. clintonius in having many more, finer, and impressed rather than raised, radials. Concentric growth lines are strongly impressed and usually result in dislocation of the radial striae when growth resumes. The striae in P. clintonius are usually raised, stronger, less crowded, and very continuous and straight. The small radials on P. clintonius appear beaded when unworn. Thus the two species are easily separated except when very young or worn. Type information.— Type: PRI 28289. Figured specimen.— A right valve (USNM 258359), a topotype specimen from 2.0 km north of the Murfreesboro town limits, right bank of the Meherrin River, Hertford County, N.C. (locality 6, USGS 26053). Stratigraphic and geographic range.— Eastover Formation (upper Miocene), rare in the Claremont Manor Member, abundant in the Cobham Bay Member in Virginia. 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. 66]
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Placopecten princepides (Emmons, 1858); L. W. Ward, 1992, Molluscan bioestratigraphy of the Miocene, middle Atlantic Coastal Plain of North America, plate 2, figure 3.
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