"Chlamys" cocoanus (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. 738, pl. 34, fig. 23]
1898 Pecten (Chlamys) cocoanus Dall, 1898
W. H. Dall, 1898, plate 34.
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«Jacksonian Eocene of Red Bluff, Mississippi, and Cocoa Post-Office, Choctaw County, Alabama; Burns.
Shell small, thin, flattish, oblique, produced behind, with about twentyfive small, low, entire ribs, rounded above, and about fourteen interstitial single smaller threads, the tops of all of which are somewhat sparsely concentrically imbricated, the interspaces showing only incremental lines; ears quite unequal, small, the posterior smaller, each with five or six low, hardly scaly radii; inside of the valve obsoletely channelled, the cardinal crura developed. Alt. 23, lat. 23 mm. This shell differs from P. membranosus by its entire and less numerous ribs, and from P. wahtubbeanus by its greater obliquity, its entire, less conspicuous, and less densely imbricated ribs.» WILLIAM HEALEY DALL, 1898
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«Discussion: This species is easily distinguished from other Chlamys in the Vicksburg Group by its high elevation, its bifurcating ribs, and its shallow in flation.
Type: Holotype 141025 USNM from the Red Bluff Formation, Cocoa Post Office, Choctaw County, Alabama.
Occurrence: Mississippi: Red Bluff Formation, localities 37, 38, 39. For other localities in the Upper Eocene of Alabama, Georgia, and South Carolina see Cooke and MacNeil (1952).»
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. 43]
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Chlamys (Aequipecten) cocoana Dall, 1898; D. T. Dockery III, 1982, Lower Oligocene bivalvia of the Vicksburg Group in Mississippi, plate 10, figure 6.
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«DESCRIPTION.— Dall's original description:
"Jacksonian Eocene of Red Bluff, Mississippi, and Cocoa Post Office, Choctaw County, Alabama; Burns. Shell small, thin, flattish, oblique, produced behind, with about twenty-five small, low entire ribs, rounded above, and about fourteen interstitial single smaller threads, the tops of all of which are somewhat sparsely concentrically imbricated, the interspaces showing only incremental lines; ears quite unequal, small, the posterior smaller, each with five or six low, hardly scaly radii; inside of the valve obsoletely channeled, the cardinal crura developed. Alt. 23, lat. 23 mm. This shell differs from P. membranosus by its entire and less numerous ribs, and from P. wahtubbeanus by its greater obliquity, its entire, less conspicuous, and less densely imbricated ribs." The above description by Dall is based solely on the holotype, a small, worn left valve. Throughout Alabama this species is usually small and worn, generally having a height of less than 20 mm. In left valves at a growth stage of 10 mm from the beak, there are about 19 to 30 low, primary ribs and 10 to 20 smaller ribs that are added by intercalation. At a distance of 10 mm from the beak in right valves, there are 23 to 30 primary ribs of which 3 to 13 of these ribs have increased by bifurcation. Well preserved, unworn specimens have imbricated external ribs. OCCURRENCE IN GEORGIA.— Chlamys cocoana is common and unusually large in the Clinchfield Sand at Area 22 kaolin pit, Huber (locality 35); common in Clinchfield Sand at Rich Hill, 4.7 miles SE of Knoxville (locality 34); rare and usually as molds in the Twiggs Clay in a ditch along Interstate 75, about 4 miles south of Perry (locality 28); common in the Twiggs Clay at a kaolin mine near Clear Creek, about 5 miles south of Gordon (locality 37); common in the Cooper Marl at a road cut 4 miles northeast of Hayneville (locality 33) (Locality 7 - Pickering, 1970); and common in Cooper Mar! at Sugar Hill, about 6 miles northeast of Unadilla (locality 30) (Locality 25 - Pickering, 1970). DISTRIBUTION ELSEWHERE IN THE SOUTHEASTERN UNITED STATES.— Chlamys cocoana is known from Upper Eocene and Oligocene localities in Alabama and Mississippi: Cocoa Post Office, Choctaw County, Alabama, Type; rare in Moodys Branch Marl, 3.9 miles west of Gilbertown (locality 6), and west bank of Tombigbee River, 100 yards north of quarry at St. Stephens, Alabama (locality 9); common in Cocoa Sand, 2.9 miles north of Grove Hill, Alabama (locality 12); common in upper Ocala Limestone, 1.6 miles southwest of Perdue Hill, Alabama (locality 14); and very rare in the basal Red Bluff at Hiwannee, Mississippi (locality 3), and at Little Stave Creek, Jackson, Alabama (locality 10). Chlamys cocoana has been reported from the Cooper Marl (Oligocene) of South Carolina (Cooke and MacNeil, 1952). My collection from the Cooper Marl at the Carolina Giant Cement Corporation quarry 2 miles north of Harleyville, South Carolina (locality 38) contains a small species of Chlamys similar to Chlamys cocoana but is probably an unnamed species. More study on this South Carolina species is needed. REMARKS.— Thirty-nine specimens of Chlamys cocoana from the Clinchfield Sand near Huber, Georgia, and one nearly complete specimen from the Cooper Marl at Sugar Hill near Unadilla, Georgia, are unusually large and well preserved. These specimens are particularly meaningful because they provide new information on the late stages of external rib development. Of the 21 left valves from Huber (height 20 to 32 mm), many specimens exhibit a rib development that is more complex than that observed on the holotype (height 23 mm). On left-valve specimens, there are 20 to 27 (avg. 24.6) prominent primary ribs and 13 to 24 (avg. 19.6) less prominent secondary ribs. The secondary ribs form between the primary ribs by intercalation. However, in some of the larger left valves, the primary ribs may also branch either into two ribs of the same height and width or add low secondary ribs at their sides, or the valves may exhibit both branching of primary ribs and addition of secondary ribs at the sides of the primary ribs. On 7 of 19 left valves, some (1 to 14, avg. 7.7) of the primary ribs have branched before the 20 mm in height growth stage. However, 11 of 19 left valves have 2 to 31 (avg. 9.9) low, secondary ribs that develop at the sides of some of the primary ribs. On 17 specimens of right valves from near Huber, Georgia, (height 20 to 28 mm) the number of primary ribs ranges from 23 to 27 (avg. 24.4). Most of the primary ribs in the central portion of the disk branch into two ribs of the same height and width at about the 10 mm-in-height growth stage. However, low secondary ribs may be added by either intercalation between primary ribs (5 of 17 specimens) or at the side of primary ribs (13 of 17 specimens) or by both means (5 of 17 specimens). The one large right valve from the Cooper Marl near Unadilla, Georgia, has rib ornamentation similar to the ornamentation just described for the right-valve specimens from the Clinchfield Sand near Huber, Georgia. Chlamys cocoana and Chlamys membranosa (Morton) are similar in internal structure (elevated margins of chondrophore, crenulated ventral margin of the disk) and general features of rib ornamentation. The two species may be distinguished, however, by differences in the details of rib ornamentation. C. cocoana has fewer external ribs than C. membranosa, and right valves of C. cocoana exhibit a characteristic branching of the primary ribs, a feature not observed in C. membranosa.» 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. 6, 7]
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Chlamys (Aequipecten) cocoana Dall; L. N. Glawe, 1974, Upper Eocene and Oligocene Pectinidae of Georgia and their stratigraphic significance, plate 2, figures 1-5, 7, 8, 10, 11.
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