"Chlamys" archiaciana (Orbigny, 1847)
ORBIGNY, A, D'. 1844-1847. Paléontologie francaise. Description des Mollusques Rayonnés fossiles. Terrains crétacés. III. Lamellibranches. 807 p., pls. 237-489. Chez Arthus Bertrand, Libraire-Éditeur, Paris. [p. 583, pl. 429, figs. 7-10]
1847 Pecten archiaciana Orbigny, 1847
A. d'Orbigny, 1844-1847, plate 429.
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«P. testa oblonga, compressa; valva inferiore radiatim inaequaliter 20-costata; costis lateribus magnis, alteris biradiatis, alteris simplicibus, transversim lamellosis; lamellis erectis; auriculis inaequalibus, transversim longitudinaiiter que costatis.
Dimensions. Largeur, 45 millim. — Par rapport à la largeur: longueur, 68/100; épaisseur, 24/100. — Angle apicial, sans les oreillelles, 78°.
Coquille oblongne, transverse, très-comprimée. Valve inférieure peu bombée, ornée de vingt côtes rayonnantes arrondies, très-inégales, les unes simples, les autres divisées en deux, bien plus larges sur les côtés qu'au milieu, sur lesquelles se remarquent des lames transversales, imbriquées, espacées, non interrompues. Les sillons qui séparent les côtes sont simples, un peu moins larges que les côtes et traversés seulement par les lames. Les oreilles sont grandes, très-inégales, ridées en travers et pourvues de quelques côtes rayonnantes. Rapports et différences. Celle espèce, qui a quelques rapports de forme avec le P. Goldfussii, s'en distingue facilement par ses côtes inégales que traversent largement des lames non interrompues. Localité. MM. d'Archiac et Baudouin de Solène l'ont recueillie aux environs d'Auxerre (Yonne), où elle paraît être rare. Explication des figures. Pl. 429, fig. 7. Valve inférieure de grandeur naturelle. De ma collection. Fig. 8. Profil. Fig. 9. Côtes grossies pour montrer les détails. Fig. 10. Profil des mêmes.» ALCIDE D'ORBIGNY, 1847
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«Discussion: The shell on n. 151 (Su Praicargiu) cearly shows the typical rib pattern of Chlamys? archiaciana. The rib number varies: some ribs divide, hence the variability in their number counted the margin of the valves. When present, the commarginallines form scale-like structures at the intersection points with the ribs. Rib number, shape, umbonal angle are also similar to the specimens described by previous authors.
Distribution: Valanginian to Aptian, but mainly Hauterivian: SE and Paris Basin in France, Switzerland, Sardinia, Bulgaria, USSR (Crimea, Caucasus, Central Asia). ? Berriasian of Tunisia (Text-fig. 13).»
DHONDT, A. V. & I. DIENI. 1988. Early Cretaceous bivalves of eastern Sardinia. Memorie di Scienze Geologiche, 40: 1-97, pls. 1-13, text-figs. 1-25. [p. 29]
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Chlamys ? archiaciana (d'Orbigny); A. V. Dhondt & I. Dieni, 1988, Early Cretaceous bivalves of eastern Sardinia, plate 6, figures 4-6.
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«Variability:
The ribnumber is extremely variable and difficult to count because it is different at the umbo and at the pallial margin, and also because it is often difficult to decide whether the paired ribs are one rib with a shallow groove in it or two ribs divided by a shallow interval. As always when primary and secondary ribs are present it is difficult on poorly preserved specimens to decide which are primary ribs and which are secondary.
The aspect of the ornamentation is different near the umbo and near the pallial margin: near the umbo the discs often seem to have a trellis-like aspect due to equally developed radial and concentric elements, whereas near the pallial margin the radial element is always predominant. Synonymy:
Though the ribnumber is extremely variable the relatively restricted occurrence of the species and the very thorough study made of it by PICTET & CAMPICHE might explain the lack of nomenclatorial problems concerning it.
The figure in D'ORBIGNY (pI. 429, fig. 7-10) are almost correct but the description not: «lames non interrompues» is an exaggeration of the concentric ornamentation which only near the umbo continuously covers ribs and intercostal intervals. Furthermore it is not true that «les cotes (sont) bien plus larges sur les cotes qu'au milieu». Differentiation:
The irregular ribdistribution makes it relatively easy to differentiate C.? archiaciana from the other Lower Cretaceous Chlamys? and Mimachlamys species.
— C.? martiniana has fewer, mostly undivided and regularly distributed ribs. — C.? goldfussi has generally fewer ribs, has larger valves, tripartite ribs on the right valve. — C.? icaunensis has a very different type of sculpture. — C.? elongata has tripartite ribs on both valves. — Mimachlamys robinaldina has narrower ribs and is completely covered with very small spines. Generic attribution:
Pecten archiacianus D'ORBIGNY, 1847, has not so far shown specimens with thimble-microsculpture but most specimens are fairly worn. Other characteristics of the species, such as the relatively narrow apical angle and the well delimited ribs, are more often found on Chlamys species; thus Pecten archiacianus is tentatively classified herein as C.? archiaciana (D'ORBIGNY).»
DHONDT, A. V. 1973. Systematic revision of the Chlamydinae (Pectinidae, Bivalvia, Mollusca) of the European Cretaceous. Part 3: Chlamys and Mimachlamys. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, 49 (1): 1-134, pls. 1-9. [p. 45-46]
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Chlamys? archiaciana (A. d'Orbigny, 1847); A. V. Dhondt, 1973, Systematic revision of the Chlamydinae (Pectinidae, Bivalvia, Mollusca) of the European Cretaceous. Part 3: Chlamys and Mimachlamys, plate 9, figure 2.
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