Chesapecten nematopleura (Gardner, 1936)
GARDNER, J. 1936. Additions to the molluscan fauna of the Allum Bluff Group of Florida. State of Florida Department of Conservation. Geological Bulletin, 14: 7-82, pls. 1-10. [p. 14, pl. 2, fig.1; pl. 3, fig. 2]
1936 Chlamys (Lyropecten) nematopleura Gardner, 1936
J. Gardner, 1936, plates 2, 3.
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«Shell large, not very heavy, sub-equivalve, sub-equilatera], showing a strong individual variation in relative dimensions, not very much inflated; apical angle greater than 90°.Tips of the umbones flattened, sculptured with 15 simple smooth rounded ribs, with smooth simple intercostal areas. Costals becoming scabrous a millimeter more or less away from the umbones and intercalaries introduded, first a medial thread, then one on either side; number of costal threads increased to three; primary ribs broadening and flattening about 3 centimeters away from the tips of the umbones and indicated on the adult shell only by a feeble rippling. Costal and intercostal threads scabrous, continuing to increase by intercalation, the sculpture toward the ventral margins suggesting that of P. clintonius of the section Placopecten although the umbones of that species are unsculptured and primary ribbing is not developed at any stage in the growth of the shell. Submargins exceedingly narrow on the right valve, wider on the left. Auricles very large, the width of the dorsal margins appreciably more than half the maximum width of the valve. Byssal groove wide, sharply delimited, incrementally furrowed. Right anterior auricle coarsely threaded with about 6 lirae radiating fan-like from the tip of the urnbone to the curved lateral margin; right posterior auricle large but not so wide as the anterior, deltoid, closely threaded with lirae similar to but finer than those upon the disk, the lateral margin almost vertical though slightly drawn in at the dorsal extremity. Left auricles imperfectly preserved but apparently similar to the right posterior auricle in size and sculpture. Ctenolium very coarse. Ligament grooves co-extensive with the dorsal margins of the auricles. Resilium deep, trigonal, the margins raised and thickened. Hinge area reinforced from the inner margin of the resilium to the outer dorsal extremities of the hinge but no defined crura observed. Adductor scars obscure. Interior retaining trace of the primary ribbing pattern which strengthen ventrally and crenate the inner margin, the lirae imilar in character to those of Amusium.
Dimension of holotype, right valve: Hight 100.0± millimeters; width, 95.0± millimeters; thickness 11.5 millimeters.
Type material: Holotype, one right valve, U. S. Nat. Mus. No. 372895.
Type locality: U. S. G. S. Sta. No. 11003, 6 miles west of Greensboro, Gadsden County, Florida.Collected by the Florida Survey. Hawthorn formation of the Alum Bluff group.
Chlamys (Lyropecten) nematopleura is closely related to Lyropecten sayanus Dall from the Oak Grove. The Hawthorn species is apparently higher although the broken specimens, of which there are many, indicate that the holotype is an abnormally high individual. The most obvious distinction is the persistence of the primary ribs in the Oak Grove species. They broaden and weaken to be sure toward the ventral margin but this tendency is not manifested so early in the growth of the shell nor is it continued to such a degree as it is in the Gadsden County material. The species C. nematopleura is common at the type locality, the only localitv in which it has been recognized, but the valves are broken though not greatly worn.
Distribution: Hawthorn formation, locality 11003 ͤ .»
JULIA GARDNER, 1936
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