"Lyropecten" duncanensis (Mansfield, 1934)
MANSFIELD, W. C. 1934. A new species of Pecten from the Oligocene near Duncan Church, Washington County, Florida. Journal of the Washington Academy of Sciences, 24: 331-333. [p. 332, figs. 1-3]
1934 Pecten (Lyropecten) duncanensis Mansfield, 1934
W. C. Mansfield, 1934, figures 1-3.
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«Shell small, rather thin, inequilateral, weakly inflated, the left valve more convex than the right. Right anterior ear with a moderately deep notch and sculptured with five rather strong radials, the innermost of which lies close to the submargin, and with transverse closely-spaced imbrications; right posterior ear with six strong, imbricated radials. Disk of right valve sculptured with 23 to 25 (24 on holotype) squarish, scabrous and imbricated ribs, separated by intervals of about the same width as the ribs. The early portion of each rib is narrowly rounded and the later portion nearly square; the latter is undercut on the sides and is ornamented on the top with three scabrous threads, the medial one of which is the strongest. The interradial spaces on the smaller specimens are either without a radial or, if present, it is only faintly indicated. A fragment of a larger shell (fig. 1, U.S.N.M. No, 373056) shows one interradial thread of moderate strength in each space. Ribs and interspaces crossed by imbrications whose edges are about one millimeter apart. Left valve sculptured similarly to the right, except that the interradial thread appears to be more strongly developed. Submargins low and marked with faint radials.
Dimensions of holotype (U.S.N.M. cat. no. 373055): Right valve, length 22.5 mm.; height, 23 mm.; convexity, 4 mm. Paratype (U.S.N.M. cat. no. 373056): Left valve (not entire), length 23+ mm.; height 23+ mm. Type locality: Station 12724, old quarry near Duncan Church, Washington County, Florida. Geologic horizon: Oligocene, Glendon formation. Pecten duncanensis is closely allied to, if not the same as, specimens figured and incorrectly referred by Dall [Dall, W. H. Proc. U. S. Nat. Museum, 51: 492, pl. 83, figs. 2, 3, 4. 1916] to Pecten suwaneënsis Dall, from the Glendon chert at Bainbridge, Ga. Cooke [Cooke, C. W. U. S. Geol. Survey Prof. Paper 133: 5. 1923] recognized that the Bainbridge material represented a new species which, however, he did not name. P. duncanensis differs from P. suwaneënsis, an Eocene Ocala limestone species, in having a higher left valve and squarer ribs which instead of being rounded are ornamented on top with tricarinate radial sculpture. There are four specimens (U.S.N.M. cat. no. 115777) in the U. S. National Museum designated as types of P. suwaneënsis. The matrix adhering to these specimens carry foraminifera which have been examined by Mr. Lloyd G. Henbest of the U. S. Geological Survey, who identifies with comparative cer- tainty Operculina floridensis Cushman and O. vaughani Cushman, both of Ocala, Eocene, age. The type of P. suwaneënsis does not appear to have been figured.» WENDELL CLAY MANSFIELD, 1934
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«Discussion: Glawe (1974) points out the superficial resemblance of Chlamys duncanensis to Pecten byramensis Gardner because of its trilirate ribs. However, it differs from the latter species in: (1) being equivalved, (2) being assymetrical and produced posteriorly, and (3) having intercalary ribs.
Type: Holotype USNM from the Suwannee Limestone near Duncan Church, Washington County, Florida.
Occurrence: Mississippi: Glendon Limestone, localities 45b, 92. For other localities see Glawe, 1974.»
DOCKERY III, D. T. 1982. Lower Oligocene bivalvia of the Vicksburg Group in Mississippi. Mississippi Department of Natural Resources, Bureau of Geology, Bulletin, 123: 1-261, pls. 1-62, text-figs. 1-48, appendix of 15 plates. [p. 45]
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Chlamys (Lyropecten) duncanensis Mansfield; D. T. Dockery III, 1982, Lower Oligocene bivalvia of the Vicksburg Group in Mississippi, plate 11, figures 4, 5, 8-10, 12.
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«OCCURRENCE IN GEORGIA.— Chlamys duncanensis is common in the upper beds at the Dixie Lime and Stone Company quarry (Oligocene) near Bridgeboro (locality 27), rare and small in the Marianna Limestone along the west bank of the Ocmulgee River at Lower City Park in Hawkinsville (locality 32), and possibly occurs in the Bainbridge area. According to Mansfield (1934, p. 33), Pecten duncanensis (now Chlamys duncanensis) is closely allied to, if not the same as, specimens figured and incorrectly referred by Dall (1916, p. 492) to Pecten suwaneensis Dall (now Chlamys suwaneensis) from the Glendon Chert (Limestone) at Bainbridge, Georgia.
DISTRIBUTION ELSEWHERE IN THE SOUTHEASTERN UNITED STATES.— Chlamys duncanensis is common in the Glendon Limestone near Heidelberg (locality 2) and rare in the Byram Marl near "old" Byram, Mississippi (locality 1); common in the Glendon Limestone near Millry (locality 8), rare in the Glendon Limestone near St. Stephens (locality 9), Glendon Flat Station (locality 11), and Frisco City (locality 15), and rare in the Byram Marl at Hart's Bridge on Five Runs Creek, Alabama (locality 18); and common in the Suwannee Limestone at Natural Bridge, Walton County (locality 21) and near Duncan Church (type locality), Washington County, Florida (locality 22). REMARKS.— Chlamys duncanensis has a trilirate rib development similar to the rib development of Pecten perplanus byramensis Gardner that also occurs in the northern Gulf Coast Oligocene formations. However C. duncanensis differs from P. p. byramensis by having interspace lirations, a convex left valve, a valve shape that is slightly produced in the posterior, and a ctenolium present in even the largest specimens-features not observed in P. p. byramensis.» GLAWE, L. N. 1974. Upper Eocene and Oligocene Pectinidae of Georgia and their stratigraphic significance. Geological Survey of Georgia, Information Circular, 46: 1-27, pls. 1-4. [p. 9]
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Chlamys (Lyropecten) duncanensis Mansfield; L. N. Glawe, 1974, Upper Eocene and Oligocene Pectinidae of Georgia, plate 3, figures 4-6, 9.
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