Carolinapecten eboreus walkerensis (Tucker, 1934)
TUCKER-ROWLAND, H. I. 1934. Some Atlantic Coast Tertiary Pectinidae. The American Midland Naturalist, 15: 612-621, pls. 25-27 [Under H. I. Tucker]. [p. 616, pl. 27, fig. 3]
1934 Chlamys eboreus walkerensis Tucker-Rowland, 1934
1939 Pecten (Chlamys) eboreus buckinghamensis Mansfield, 1939
1939 Pecten (Chlamys) eboreus buckinghamensis Mansfield, 1939
H. I. Tucker, 1934, plate 27.
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«Description. — Shell thin; very inequilateral; larger than typical eboreus; auricles smaller, nearly equal. Usually 20 low, rounded, widely spaced ribs. Some specimens have 24 ribs. Concentric sculpture of wavy, elevated lamellae which are much more closely spaced from the umbonal region to the ventral margin. The ribs on very large shells become nearly obsoIete at the margins. Valves nearly equally convex; margins scalloped. Only concentric sculpture anteriorly and posteriorly. At the posterior margin the left valve is markedly depressed and produced. Dimensions. — height 88, width 113, hinge 41.5, convexity 23 mm.
Remarks. — C. eboreus Conrad, s..s., from the type locality is more equiIateral and more strongly ribbed. However, valves vary widely and this subspecies represents the extreme of a line of development. This subspecies has fewer rib, usually; is commonly more strongly lamellated and has the characteristic depression in the posterior portion of the left valve. Occurrence. — Wacnmaw Pliocene. Walkers, N. C. (type ); Nixon's Landing on Waccamaw River, S. C., Dr. Burnett Smith. Holotype. — A left valve. Collection Paleontologial Research lnstitution, Ithaca, New York. Paratypes.— From Nixon's Landing, S. C., CoIIection Dr. Burnett Smith, Skaneateles, New York.» HELEN lONE TUCKER-ROWLAND, 1934
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«Description: Shell very large, subcircular, thin; right and left valves convex, compressed; ribs 20 to 24, low, narrow, with wide interspaces; posterior margin produced, left valve depressed, warped posteriorly.
Occurrence: Pliocene. Carolinas – upper Goose Creek Limestone. Raysor; Florida – Buckingham Limestone. Type locality: Walker's Bluff, Cape Fear River, North Carolina. Discussion: This is the largest of the Carolinapecten stock, with exceptional specimens exceeding 20 cm in maximum diameter. No other lineage or variety shows the pronounced expansion of the posterior margin or the warped cross section. Mansfield (1936, p. 174) erroneously synonymized C. e. walkerensis with Dall's (1900) Pecten ebureus senescens. The latter, which is the smallest of the forms of Carolinapecten, has subdued, nearly obsolete radial ribs, and a more inflated shell. This synonymy was accepted by Tucker-Rowland (1938, p. 50). Meanwhile, Mansfield (1939) described Pecten eboreus buckinghamensis from the Buckingham Limestone. The latter taxon was also described as large and having a warped cross-section, both traits uniquely shared with C. e. walkerensis. The warped cross-section becomes more obvious in specimens greater than approximately 10 cm in maximum diameter. In situ, abundant populations of C. e. walkerensis seem restricted to the Raysor Marl and the equivalent upper Goose Creek Limestone. Tucker (1934) designated a type locality of Walkers Bluff, Cape Fear River, North Carolina. However,
she also cited a paratype from Nixon's, a classic Waccamaw locality, and USC Spartanburg collections contain single valves from basal Waccamaw beds at Calabash, North Carolina. In the Natural Well Duplin faunas, a smaller, more symmetrical Carolinapecten ebureus var. darlingtonensis (Dall) replaces the older walkerensis morphology. The reappearance of very rare, unpaired walkerensis valves in the Waccamaw consequently represents either retrograde evolution, an undetected surviving lineage, or reworking of older, Goose Creek specimens. At both Calabash and Nixon's, the Waccamaw rests unconformably on Cretaceous strata and contains reworked species. We consider the Waccamaw records of C. e. walkerensis to be fortuitous.» CAMPBELL, M. R. & L. D. CAMPBELL. 1995. Preliminary Biostratigraphy and Molluscan Fauna of the Goose Creek Limestone of Eastern South Carolina.Tulane Studies in Geology and Paleontology, 27 (1-4): 53-100, pls. 1-5. [p. 76]
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Carolinapecten eboreus walkerensis (Tucker); M. R. Campbell & L. D. Campbell, 1995, Preliminary Biostratigraphy and Molluscan Fauna of the Goose Creek Limestone of Eastern South Carolina, plate 3, figure 1; plate 5, figures 1, 2.
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«C. eboreus walkerensis (Tucker, 1934) (synonym: Pecten eboreus buckinghamensis Mansfield, 1939) is an exceptionally large, stratigraphically important subspecies with a warped cross section. It is from the upper Goose Creek Limestone of South Carolina, and was erroneously synonymized with Carolinapecten eboreus senescens (Dall, 1898) by Mansfield, 1936. The latter is a small subspecies with obsolete sculpture which is restricted to the Waccamaw faunas.»
CAMPBELL, L. D. 1993. Pliocene molluscs from the Yorktown and Chowan River Formations in Virginia. Virginia Division of Mineral Resources Publication, 127: 1-259, pls. 1-43. [p. 24]
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