Chesapecten coccymelus (Dall, 1898)
DALL, W. H. 1898. Contributions to the Tertiary fauna of Florida. Silex Beds of Tampa and the Pliocene Beds of the Caloosahatchie River. Part IV. I. Prionodesmacea: Nucula to Julia. 2. Teleodesmacea: Teredo to Ervilia. Transactions of the Wagner Free Institute of Science of Philadelphia, 3 (4): viii, 571-947 p., pls. 23-35 (pls. 36 and 37 in part 5, 1900). [p. 741, pl. 34, fig. 1]
1898 Pecten (Chlamys) coccymelus Dall, 1898
1938 Chlamys (Lyropecten) madisonius bassleri Tucker-Rowland, 1938
1938 Chlamys (Lyropecten) madisonius bassleri Tucker-Rowland, 1938
W. H. Dall, 1898, plate 34.
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«Miocene of Plum Point, Maryland; Clark.
Shell small, ovate, inflated, strongly sculptured, with unequal ears; disk with eighteen narrow, high, compressed ribs, with wider interspaces, which near the basal margin carry one or two very small radial threads; the backs of the ribs support numerous high, evenly spaced, distally guttered, small spines; in the interspaces only transverse sculpture of wavy incremental lines; submargins small, narrow, with fine, beaded radial threads, which in the left valve also extend over the ears; hinge-line short, the cardinal crura developed, sharply cross-striated; auricular crura present; interior of the disk fluted in harmony with the external ribs. Alt. 30, lat. 25, semidiam. 5 mm. A single left valve of this elegant species was obtained. From the young of P. Madisonius, which sometimes approach it, it is easily distinguished by its more oval and inflated form, nearly smooth interspaces, and compressed ribs.» WILLIAM HEALEY DALL, 1898
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«Discussion.— Specimens available to Whitfield (1894) and Richards and Harbison (1942) were all juveniles or fragments and were identified as “Pecten madisonius” by those authors. That species occurs only in the upper Pliocene strata of the Yorktown Formation and its stratigraphic equivalents to the south (Ward and Blackwelder, 1975). Gibson (1987) and Ward (1992) have more recently described and illustrated Chesapecten coccymelus. The specimens from Delaware are typical of the species, but none exhibit the extreme development of the center row of scales on the ribs that was described by Dall (1898). The material recovered consists of more than 20 nearly complete valves and numerous fragments. The species is relatively small with adults averaging 40 mm. It is also abundant in Bed 10 of the Plum Point Marl Member.
Geologic range.— Kirkwood Formation; Calvert Formation, Fairhaven Member (Bed 3A), Plum Point Marl Member (Beds 4 and 10).» WARD, L. W. 1998. Mollusks from the Lower Miocene Pollack farm site, Kent County, Delawere: a preliminary analysis. In: R. N. Benson, ed., 1998, Geology and paleontology of the lower Miocene Pollack Farm Fossil Site, Delaware: Delaware Geological Survey Special Publication No. 21, p. 59-131. [80]
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Chesapecten coccymelus (Dall); L. W. Ward, 1998, Mollusks from the Lower Miocene Pollack farm site, plate 11, figures 1, 2, 6.
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«Discussion.— Chesapecten coccymelus is a small Chesapecten, usually less than 60 mm in height, having very high distally concave spines and unequal auricles, the anterior auricle being longer than the posterior.
Plicae of right valve number 15-19, each plica strongly sculptured with one to three rows of very high distally concave spines and with one to three rows of less elevated spines in the interspaces. Chesapecten coccymelus differs from C. nefrens in being smaller (average adults being only 40-50 mm long, as opposed to 150 mm for C. nefrens), in its rows of very high distally concave spines, and in its unequal auricle size, the anterior auricle being longer than the posterior. Dall's original specimen is an end member of a somewhat variable species. A comparison of the holotype and other specimens shows that the number of rows of spines on the ribs is a variable character. This species is common in Bed 10 of the Plum Point Marl Member of the Calvert Formation. Mongin (1959) suggested that a new name, calvertensis, be applied to several species, including C. bassleri (Tucker-Rowland). The name calvertensis does not have priority and cannot be used. In addition, the species intended to be grouped under that name do not appear to be closely related. Type information.— Holotype: USNM 87 7 54. Type locality: Plum Point, Md. Figured specimen.— Plate 20, figure 1: Right valve (USNM 405208) from 0.5 miles below Camp Roosevelt, westem shore of the Chesapeake Bay, Calvert County, Md.; Plate 20, figure 3: Ieft valve (USNM 405209) from the same locality. Stratigraphic and geographic range.— Calvert Formation, Plum Point Marl Member, Bed 10 (lower middle Miocene) in Maryland. Pungo River Formation (lower middle Miocene) in North Carolina.» 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. [p. 72]
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Chesapecten (Chesapecten) coccymelus (Dall 1898); L. W. Ward, 1992, Molluscan bioestratigraphy of the Miocene, middle Atlantic Coastal Plain of North America, plate 20, figures 1, 3.
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«Occurrence.— The type locality is the Calvert Formation, Plum Point, Md. Additional localities are Zone 10 (Shattuck, 1904) of the Calvert Formation from Randall Cliff (fig. 1, loc. 1; USGS loc. 25293) south to Plum Point (fig. 1, loc. 2, USGS loc. 25294) .
Comparison and remarks.— Chesapecten coccymelus differs from C. nefrens in its smaller size (average adults being only 40 to 50 mm long as opposed to 150 mm for C. nefrens), its rows of very high distally concave spines, and its unequal auricle size, the anterior auricle being longer than the posterior. Dall's original specimen is an end member of a somewhat variable species. We have provided a new description which includes the more morphologically typical specimens of this species. A comparison of the holotype (pl. 3, fig. 1) and our specimen (pl. 3, fig. 2) shows that the number of rows of spines is a variable character. Contrary to Dall's original description, we consider the cardinal crura in this species to be reduced, especially in adult specimens. This species is common in Zone 10 of the Calvert Formation. Mongin (1959) suggests that a new name, calvertensis, be applied to several species, including C. bassleri (Tucker-Rowland). The name calvertensis does not have priority and cannot be used. The species intended to be grouped under this name do not appear to be closely related.» WARD, L. W. & B. W. BLACKWELDER. 1975. Chesapecten, a new genus of Pectinidae (Mollusca: Bivalvia) from the Miocene and Pliocene of eastern North America. United States Geological Survey Professional Paper, 861: 1-24. [p. 9]
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Chesapecten coccymelus (Dall); L. W. Ward & B. W. Blackwekder, 1975, Chesapecten, a new genus of Pectinidae, plate 3, figures 1, 2.
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