Palliolum gerardi (Nyst, 1835)
NYST, P. H. 1835. Recherches sur les coquilles fossiles de la province d' Anvers. 36 pp., pls. 1-5. Bruxelles [p. 19, pl. 3, fig. 75]
1835 Pecten gerardii Nyst, 1835
1840 Pecten subdiaphanus Wood, 1840
1840 Pecten subdiaphanus Wood, 1840
Pecten Gerardi Nyst; P. H. Nyst, 1845-1846, Description des coquilles et des polypiers fossiles des terrains tertiaires de la Belgique, plate 18, figures 11a, 11b.
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«Car. sp. Coquille orbiculaire, mince, déprimée, lisse, à stries. fines concentriques très-rapprochées, coupées par d'autres longitudinales visibles vers les bords; à oreillettes inégales; intérieur des valves muni d'une tache ronde blanche, nacrée, qui prend naissance sous les crochets, et dépasse la moitié de la coquille.
Localité. ANVERS; elle n'y est pas rare, elle à quelque ressemblance avec le Pecten cornea Sow., mais l'absence des 2 dents sous les crochets, ainsi que d'autres caractères, nous ont déterminés à en faire une nouvelle espèce que nous dédions à feu M. Gérard. Mon cabinet, et ceux de MM. Duchastel et Kickx. Observation. Les espèces de ce genre, étant très-difficiles à déterminer, nous supposons que par la suite l'on pourra en trouver plusieurs qui nous ont échappées; nous nous bornons à décrire les mieux caractérisées.» PIERRE HENRI NYST, 1835
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«Description. — Shell rather small (height up to c. 48 mm), fragile, suborbicular to orbicular, inequilateral, nearly equivalve, not bulbous, left valve more convex than right valve, umbonal angle 90-100°, auricles unequal, antimarginal microsculpture present.
Both valves macroscopically smooth or minutely sculptured with close-set radial riblets starting below the central section of the disc and increasing in number toward the marginal area. Anterior auricles with 4-6 fine radial riblets, with overrunning concentric lamellae. Posterior auricles with 6-8 fine radial riblets. Byssal notch fairly shallow. Ctenolium present with 3-5 active teeth. Hinge line straight. Resilial insertion somewhat triangular oval. Inside ventral margin finely plicated in specimens preserving an external radial sculpture near the margin. Colour pattern frequently preserved in the umbonal area, consisting of a central light coloured part, sharply separated from two darker areas along the posterior and anterior dorsal margins, enclosing an apical angle of ca. 60°. Stratigraphic distribution. -- P. gerardi is exclusively known from the Pliocene (Kattendijkian and Scaldisian) of the North Sea Basin. In Belgium it is found in the Kattendijk and Lillo Formations (upper part of the Kattendijk Sands, Luchtbal Sands and, probably reworked, in the Oorderen Sands). In Great Britain this species is locally abundant in the Coralline Crag.» JANSSEN, A. W. & H. H. DIJKSTRA. 1996. Morphological differences between two species of Palliolum (Bivalvia: Pectinidae). Basteria, 59: 107-113, figs. 1-9. [109, 112]
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Palliolum gerardi (Nyst, 1835); A. W. Janssen & H. H. Dijkstra, 1996, Morphological differences between two species of Palliolum, figures 9a, 9b.
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«Shell orbicular, subpellucid, inequivalved or somewhat plano-convex, equilateral, externally covered with fine longitudinal rays, visible only near the margin, and beautifully sculptured with diverging or divaricating striae, auricles unequal.
Diameter, 2 inches. Locality. Cor. Crag, Ramsholt, Sudbourn, and Gedgrave. This beautiful species is exceedingly abundant at the latter locality, where, however, the valves are always separated. At Ramsholt, they are somewhat less abundant, and the valves are there found in their natural position. From the figure and description given by M. Nyst, above referred to, there is little doubt, that the English Crag shell is the same as the one found in the Campinian beds of Belgium. Our shell is very thin, but strong, with irregularly-marked lines of increase; the right valve always more or less flattened, while the opposite one is tumid or convex. Auricles very unequal and rayed, or costated, with a moderate sized opening beneath the anterior one of the right valve, this is almost obliterated in the adult shell, a rather large triangular cartilaginous area overhanging or projecting into the interior. The impression formed by the edge of the mantle parallel with the margin, and extending to about two thirds the length of the shell, that by the adductor, less distinctly defined. The contour of the shell is nearly circular, a little interrupted with a pair of rather high shoulders. A dark line diverges from the umbo, within which the shell is of a lighter colour, like that in P. corneus, being, however, perfectly distinct from that species. The beautifully curved or divaricating striae (from the absence of longitudinal or radiating ribs), are visible upon the smooth surface of the shell with the naked eye. An American fossil, Pecten Virginianus, Conrad. "Foss. of the Med. Tert. of the United States," p. 46, pl. 21, fig. 10, 1838, appears to resemble our shell in many characters, but from the representation it differs in being longer than high, and has the ears more equal and larger.» WOOD, S. V. 1851-1860. A Monograph of the Crag Mollusca, with descriptipns of shells from the upper Tertiaries of the British Isles. Vol II. Bivalves. Paleontographical Society [Monograph, 1851-1861] [p. 25]
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Pecten Gerardii Nyst; S. V. Woods, 1851-1860, A Monograph of the Crag Mollusca, plate 5, figures 5a, 5b.
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