Pixiechlamys quemadensis (Ihering, 1897)
IHERING, H. VON. 1897. Os molluscos dos terrenos terciarios da Patagonia. Revista do Museu Paulista, 2: 217-382, pls. 3-9. [p. 228, pl. 6, fig. 38]
1897 Pecten quemadensis Ihering, 1897
H. von Ihering, 1897, plate 6.
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«Pecten testa subaequivalvi, aequilaterali ovata, liris radiantibus circa 60 squamuliferis irregulariter geminatis vel trigeminis munita; auriculis inaequalibus, anteriore sub incisura byssali in valva dextra dentata.
Long. 31, Alt. 37, Diam. (½) 7 Mm.
Form. santacruzensis (La Cueva; Jegua quemada).
Esta espécie é bem parecida ao Pecten geminatus de Sowerby, de modo que ao principio julguei estas conchas como variedade daquella especie. E, porem, na nossa espécie de Santa Cruz o numero das estrias muito maior, cerca de 90 ou mais contra 22 em geminatus e alem disto as mesmas não estão dispostas com regularidade em pares. Existem ao lado anterior e posterior estrias finas em numero de cerca 7—10 de cada lado. Seguem-se, depois, as estrias maiores aggrupadas ás vezes por 2 ou por 3, mas sem regularidade, de modo que não existe differença certa entre os intervalles que separam as costas e os que dividem as estrias secundarias de um grupo. Nos intervalles apparecem ás vezes estrias mais finas. As estrias principiam das vertebras em numero de cerca de 30 e augmentam para a borda ventral cada vez mais. As estrias são munidas de escamas. Das auriculas a anterior é muito maior, sendo munida de 5—6 estrias radiarias. Em baixo da auricula segue, na borda anterior na extensão de 3 Mm. a serra byssal, composta de 6 denticulos. A superficie interior da concha é plicada, conforme ás estrias. A valva esquerda é menos convexa do que a outra. Esta espécie está intimamente ligada á precedente [Pecten nodosoplicatus sp. n.] e não sei se bem procedi separando-as, podendo talvez ambas estas espécies novas representar apenas variedades de uma espécie extremamente variavel.» HERMANN VON IHERING. 1897
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«Type specimens.— Holotype MACN-Pi 272, a right valve from Las Cuevas (Santa Cruz Province), Monte León Formation (early Miocene).
Diagnosis.— Shell small and equiconvex. Posterior auricles tiny. Byssal sinus very deep. Valves sculptured with bunches of up to three fine ribs.
Occurrence.— Monte León Formation (early Miocene) at Las Cuevas and Yegua Quemada; Chenque Formation (early Miocene) at Curva la Calera, Punta Maqueda, Punta Delgada, Rada Tilly, Baliza Villegas, Punta Borjas, and Cerro Chenque; and San Julián Formation (early Miocene) at Punta Nava.
Description.—Shell small, up to 52 mm high, thin, subcircular in outline, higher than long, equiconvex, acline or slightly prosocline, and elongate posteriorly; dorsal margins of disc concave and steeply inclined ventrally. Hinge dorsal margin straight, 51%–61% of total disc length. Umbonal angle 84°–94°. Auricles strongly asymmetrical, anterior auricles up to four times as long as posterior auricles, which are tiny; auricles with free margins concave and sloping anteriorly, except for that of left anterior auricle, which is strongly sinuous; right anterior auricle with dorsal margin straight, not projected upward, free margin rounded; byssal notch rectangular, very deep, moderately wide, with functional ctenolium throughout ontogeny, with five or six strong teeth; byssal fasciole narrow with corrugations convex toward umbo; byssal sinus very deep. Right auricles sculptured with 5–7 radial ribs, left anterior auricles with 8–14 ribs, left posterior auricles with 7–9 ribs; anterior auricles with thicker ribs than on posterior auricles. Disc sculptured with low, narrow, rounded radial ribs covered with closely packed ventrally concave scales, with interspaces each narrower than one rib; ribs covered with three orders of riblets appearing at 3–10 mm, 16–25 mm, and 40–50 mm height from beaks. Both valves of most specimens with one or two growth ledges. Right valve sculptured with 12–16 primary ribs that bifurcate at 1–2 mm and at 4–19 mm height from beaks, most of them clustered into groups of 2 or 3 ribs, reaching a total of 60 ribs near ventral margin of adult specimens. Left valve ornamented with up to 70 ribs of two orders that become equal in width in adults. Antimarginal, shagreen, and commarginal microsculptures developed on both valves; antimarginal ridgelets appear at beginning of radial stage, expanding over entire surface; shagreen microsculpture present in one or two bands between 4–10 mm and 30–40 mm height from beaks; commarginal sculpture developed from initial radial stage to 3 mm height from beaks; antimarginal sculpture present on posterior auricles, commarginal sculpture on right anterior auricle, in proximal area of left anterior auricle, and in some specimens, on right posterior auricle.
Materials.— Two articulated specimens, 16 right valves, and 13 left valves: MACN-Pi 271, MACN-Pi 6159, MACN-Pi 6400, MACN-Pi 6403, MACN-Pi 6017; MLP 2421; MLP 2998, MLP 8448; CPBA 8516, CPBA 21581, and CPBA 23621–23623.
Dimensions (in mm).— Holotype MACN-Pi 272, L = 31.0, H = 36.0; MLP 8448, L = 37.6 , H = 41.2; MLP 2998, L = 19.0, H = 22.7; MLP 8448, L = 37.6, H = 41.2; MLP 2998, L = 27.5, H = 28.0.
Remarks.— Ihering (1897) described this species based on a right valve from Las Cuevas (Santa Cruz Province, Monte León Formation, early Miocene) and suggested that Pixiechlamys quemadensis n. comb. and Pecten nodosoplicatus Ihering, 1897, today placed in Swiftopecten iheringii del Río, 1995, could be one variable species. However, in 1907 he considered them to be separate taxa. Ortmann (1902) considered Pixiechlamys quemadensis n. comb. to be a variety of Pecten geminatus and illustrated one specimen from Cañadón Darwin (Ortmann, 1902, pl. 23,fig. 2d), but that specimen is herein considered to be Chokekenia nicolasi n. comb. (Morra, 1985).
SANTELLI, M. B. & C. J. DEL RÍO. 2019. Neogene Pectinidae (Bivalvia) of tribe Chlamydini Teppner, 1922 in Patagonia (Argentina): Zygochlamys Ihering, 1907 and three new genera. Journal of Paleontology, 93 (2): 312-336, figs. 1-11. [p. 327-329]
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Pixiechlamys
quemadensis (Ihering, 1897) n. comb.; M. B. Santelli & C. J. del Río, 2019,Neogene Pectinidae (Bivalvia) of tribe Chlamydini Teppner, 1922 in Patagonia (Argentina): Zygochlamys Ihering, 1907 and three new genera, figures 8.8-8.13, 9.1. |