"Batequeus" ducenticostatus D. C. Campbell, 1995
CAMPBELL, D. C. 1995. New molluscan faunas from the Eocene of South Carolina. Tulane Studies in Geology and Paleontology, 27: 119-152, pls. 1-9. [p. 128, pl. 1, fig. 8; pl. 2, figs. 1, 2; pl. 3, figs. 1, 2]
1995 Batequeus ducenticostatus Campbell, 1995
D. C. Campbell, 1995, plates 1-3.
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«Chlamys n. sp. COOKE and MACNEIL, 1952, U S. Geol. Survey. Prof. Paper 243-B, p. 26.
? Chlamys cocoana Dall. COOKE and MACNEIL, 1952, U.S. Geol. Survey, Prof. Paper 243-B, p. 26, 27; PALMER and BRANN, 1965, Bulls. Arner. Paleontology, v. 48, p.82. ? Pecten cocoanus Dall. WARD et al., 1979, South Carolina Geol. Notes, v. 23, p. 23, 32; WARD and BLACKWELDER 1980, in R. W. FREY (ed.), Excursions in Southeastern Geol., v . 1, p. 196; DUBAR et al., 1980, ibid., v. 1, p. 236. ? Chlamys cf. C. cocoana (Dall. POWELL and BAUM, 1982, Geol. Soc. Amer., Bull., v. 93, p. 1105. Description: Adult shell produced posteriorly, adult height slightly less than length (maximum 55 mm), juvenile taller than long. Anterior auricle with fine radial sculpture, concentric growth lines prominent near byssal notch; byssal notch shallow; dorsal margin straight or slightly concave; posterior auricle with very faint, fine radial sculpture, narrow and smaller than anterior auricle. Shell thin. Left valve sculpture of about 25 primary radial ribs, which may bifurcate; first intercalary ribs (secondary ribs) appear at about 5 to 6 mm below beak and become equal to the primary ribs in size (about 0.5 mm wide at ventral margin in adult), later intercalary ribs (tertiary ribs) remaining narrower (0.3 mm at ventral margin; almost no interspace in well-preserved areas; fine scales not aligned from rib to rib. Right valve sculpture similar; about 30 primary ribs, with a greater trend towards bifurcation than in left valve; additional intercalary ribs possible, becorning equal in width to tertiary ribs, producing a pattern or three smaller ribs between each pair or large ribs in the center of the ventral edge. Sculpture or both valves finer towards anterior and posterior margins; easily eroded to form smooth, threadlike ribs with interspaces narrower than the ribs.
Holotype: USNM 466955. Paratypes: USNM 466956; UNC 12248a. Type locality: Giant Portland cement quarry, north of Harleyville, South Carolina. All known specimens of this species are from this locality. Etymology: Adults have about 150 more ribs than any other Eocene scallop in the region; hence, "two hundred-ribbed'' is a useful distinguishing feature. Discussion: This species closely resembles Batequeus mezquitalensis Squires and Demetrion (1990), the type species of Batequeus. They are similar in size and shape, being slightly longer than high as adults. The valves in both species seem equally low-convex, but I do not have any articulated pairs of B. ducenticostatus for direct comparison. The byssal notch in both is small, but in B. ducenticostatus the anterior auricles are larger than the posterior ones, unlike B. mezquitalensis.
Both species have left valves with numerous very closely spaced riblets, though the scales are discontinuous and more widely spaced in B. ducenticostatus, as opposed to the "imbricated growth lines" of B. mezquitalensis. The right valve sculpture is more distinctive. Both have 25-30 primary ribs, but in B. mezquitalensis they are low, flat-topped, and can be grooved, unlike the fine, ungrooved, scaled riblets of B. ducenticostatus, which are similar to those of the left valve. Intercalary ribs are present on both valves of both species. In the largest specimens of B. ducenticostatus, three sets of intercalary ribs may be present, in addition to some bifurcation of primary ribs, producing a total of over 200 ribs ventrally. As noted by Squires and Demetrion (1990), Batequeus is assignable to the Chlamys group of Hertlein (1969). It seems closely related to the New Zealand genus Serripecten. Batequeus ducenticostatus is distinct from all other known Eocene species from the eastern United States. The sculpture of the various forms in the type lot of Chlamys membranosa is finer but otherwise similar to that of B. ducenticostatus, but the latter attains a larger maximum size and differs greatly in shape. Chlamys cocoana (Dall,1898) is similar in overall outline to B. ducenticostatus, but has wider, more irregular primary ribs and wider interspaces without the rapid development of intercalary ribs. Also, the type of C. cocoana is probably from the Oligocene (Cooke and MacNeil, 1952). Glawe (1974, pl. 2) figures what appear to be at least three species under this name, all of which have taller, wider primary ribs and less well-developed intercalary ribs than B. ducenticostatus. However, the form(s?) represented by his figures 1, 4, 7, and 8 are similar in shape of auricle and overall outline to B. ducenticostatus. Records from the Cooper Formation of Chlamys cocoana (Ward et al., 1979, p. 2 3; Ward and Blackwelder, 1980, p. 196; Cooke and MacNeil, 1952; Glawe, 1974) may represent true C. cocoana or B. ducenticostatus (in that case, the specimens probably were from the "Cross" and not the Cooper), or they may represent a new species.» DAVID C. CAMPBELL, 1995
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«A second species of Batequeus, B. ducenticostatus Campbell, 1995, from the "Cross Formation" of probable Bartonian age of South Carolina, is not a Batequeus but rather is a member of the Chlamys group. Its radial sculpture is similar on the two valves, and its radial costae are more densely packed, more densely scaly, and with a more complex introduction pattern throughout ontogeny than in any member of the Batequeus-Serripecten clade.»
WALLER, T. R. 2006. New Phylogenies of the Pectinidae (Mollusca: Bivalvia): reconciling Morphological and Molecular Approaches. In: S.E. Shumway & G.J. Parsons (Ed.), 2006: Scallops: Biology, Ecology and Aquaculture, 1-44, figs. 1.1-1.4. [p. 16]
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