Pecten (Plagioctenium) gibbus carolinensis Grau, 1952
GRAU, G. 1952. A new subspecies of Pecten (Plagioctenium) gibbus (Linné, 1758). The Nautilus, 66: 17-18. [p. 17, pl. 1, figs. 2-5, 7]
«PECTEN (PLAGIOCTENIUM) GIBBUS CAROLINENSIS subsp. nov. Plate 1, figs. 2, 3, 4, 5, 7.
Shell of moderate size, equilateral, equivalve and moderately convex, with fairly long hinge line. Anterior auricle of right valve rather strongly produced and having 4 riblets. Fine concentric lamellae in interspaces and crossing riblets, often producing scales on apexes. Distinct byssal sinus and ctenolium consisting of 5 or 6 teeth. Posterior auricle moderately produced and having 6 or 7 riblets. Fine lamellae in interspaces of young shells; in larger specimens lamellae cross riblets but do not form scales. External hinge margin of right valve irregularly scaled, but not prominently. Anterior and posterior auricles of left valve having 5 to 7 riblets ; concentrically lamellated but not scaled. Disc of both valves having 18 to 21 ribs. On right valve ribs are rather broad and rounded, with distinct concentric lamellae (much stronger than on auricles) in interspaces. Ribs on left valve narrower, steeply rising and somewhat flattened on top. Intercostal lamellae more numerous than on right valve, and in juvenile specimens present in interspaces only. As shell reaches altitude of 20 to 24 mm. lamellae continue across ribs. Umbones not gibbous, tapering to point and, in left valve only, projecting slightly over hinge line. Coloration: left valve ranging from reddish brown to pale brown, variously mottled with white and deep brown. Right valve paler and often predominantly white; mottled with colors corresponding to those of left valve ; anterior auricle always white. The holotype, in the author's collection, was taken at a depth of 80 feet, 2 miles off Port Royal, South Carolina, by Mr. R. C. Spencer. It measures: height 33 mm.; length 34 mm.; diameter 14 mm. Paratypes have been deposited in the United States National Museum and the California Academy of Sciences, San Francisco. The subspecies is easily distinguishable from typical gibbus, the following constant features being the chief differences: valves much less convex, interspaces distinctly lamellated, byssal and posterior sinus pronounced and umbones pointed and not inflated. As an indication of relative tumidity (the most immediately apparent distinction) an average specimen of P. gibbus measuring 33 mm. in height, has a diameter of 19.5 mm., while the holotype of the subspecies, of the same height, has a diameter of only 14 mm. The author is grateful to Mr. Spencer for so generously supplying specimens, to Mr. Herman Gunter, of the Florida Geological Survey, for the loan of fossil material, and, in connection with research in general on the family Pectinidae, to Mr. Leo G. Hertlein of the California Academy of Sciences, who has, for several years, given assistance and advice of immeasurable value.» GILBERT GRAU, 1952
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G. Grau, 1952, plate 1.
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