Reticulochlamys zinsmeisteri Del Rio, 2004
DEL RÍO, C. J. 2004. Revision of the large neogene pectinids (Mollusca: Bivalvia) of Eastern Santa Cruz and Chubut Provinces (Patagonia: Argentina). Journal of Paleontology, 78 (4): 690-699, figs. 1-6. [p. 693, figs. 4.7, 4.9]
2004 Reticulochlamys zinsmeisteri Del Rio, 2004
C. J. del Río, 2004, figure 4.
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Pecten praenuncius IHERING, 1907. ORTMANN, 1902, p. 115, pl. 19, fig. 2a.
«Diagnosis.— Acline, medium shell, weakly inflated, with the two valves equally inflated, and with exterior surface weakly folded by extremely low flat plicae. Auricles small, subequal; free margin of auricles inclined towards anterior. Shagreen microsculpture only well developed on left valve, commarginal lirae dominant on right valve throughout ontogeny.
Description.— Shell acline, of medium size, up to 100 mm, weakly inflated, nearly equidimensional, both valves equally inflated, or left valve slightly more inflated than right. Umbonal angle 110 degrees. Auricles small, subequal; dorsal margin straight; hinge length 48–50 percent of total shell length; free margin of auricles inclined anteriorly; shallow byssal notch present in adult stage, ctenolium with one strong tooth. Valves only weakly folded with five broad, flattened plicae, with the lateral ones hardly visible, evenly ornamented with widely spaced, smooth, low, fine riblets, more prominent on left valve than right. Microsculpture of antimarginal ridgelets and commarginal lirae that appear early in ontogeny at heights of about 20–25 mm from beaks; commarginals dominant, persistent, and uniform across riblets throughout growth on right valve. Shagreen microsculpture restricted to early ontogeny on disc flanks and to narrow strips on discs of right valve, but prominent on left valve, where it covers entire surface. Preradial stage unknown; first 20 mm of right valve characterized by very fine radial costae that disappear later. Etymology.— In honour of William Zinsmeister, who collected the type material of this species. Type.— Holotype MACN—pi 4648, a right valve from Monte Entrada (Monte León Formation, Early Miocene); length: 98 mm, height: 110 mm. Other material examined.— Three valves, EASPU 309, MACN—pi 4649–4650. Occurrence.— Monte Entrada, middle section of the Monte Leon Formation. Discussion.— Reticulochlamys zinsmeisteri is restricted to the fossiliferous beds exposed at Monte Entrada where it is associated with R. proximus (Ihering) and abundant specimens of Struthiolarella patagonensis Camacho and Zinsmeister, 1989 and S. ameghinoi (Ihering, 1897). It differs from Reticulochlamys proximus in having smaller and more nearly equivalve shells, shorter auricles with free posterior auricle margins inclined posteriorly, valve surfaces only weakly folded by the development of extremely low and flattened plicae, and with shagreen microsculpture only well developed on the left valves. Reticulochlamys zinsmeisteri is easily distinguished from R. borjasensis n. sp., mainly because R. borjasensis has strongly inequivalve shells, with prominent plicae sculptured with scaly riblets.» CLAUDIA JULIA DEL RÍO, 2004
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