"Chlamys" icaunensis (Cotteau, 1855)
COTTEAU, G. 1853-1857. Études sur les Mollusques fossiles du département de l'Yonne. 141 p. Baillière, Paris [p. 110, 115]
1855 Pecten icaunensis Cotteau, 1855 [partim]
Pecten (Chlamys) icaunensis Cott.; S. Gillet, 1921, Etude de la faune de lamellibranches du calcaire à Spatangues (Hauterivien supérieur), plate 5, figure 4.
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«— ICAUNENSIS, Cot., 1855. Gy-l'Evêque Etage néocomien.
Très-belle espèce, oblongue, comprimée, ornée de seize à dix-huit l'côtes droites et rayonnantes. Sillons intermédiaires larges et garnis de stries rayonnantes, fines, régulières, granuleuses, avec lesquelles se croisent d'autres stries concentriques. Oreillettes grandes et striées.»
GUSTAVE COTTEAU, 1855
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«Description:
Diagnosis.-- Chlamys? species of medium size, covered with 16-18 relatively broad radial ribs; the disc is completely covered with a trellis-like ornamentation consisting of very fine radial and concentric striae.
Ornamentation: the trellis-like ornamentation is the same on both valves; the striae are so fine that the discs look as if they were; covered with little square cavities. On both valves the intercostal intervals are broad; on the right valve the ribs have a triangular, sharp, transection, whereas on the left valve they have a rounded transection. The auricles are covered with the same ornamentation but the radial element is more pronounced than on the valves; the auricle shape is the same as on the other Chlamys species. Discussion
The unusual ornamentation of Chlamys? icaunensis is very close to the thimble-microsculpture characteristic of the genus Chlamys, but the cavities present on the former form squares whereas those on the latter group form rhombs. As far as could be checked the square element is not known in any other Chlamys species from Cretaceous or Tertiary deposits.
I have not seen any complete specimen of this species. The ornamentation is so unusual that it is possible to recognize even fragmentary specimens of the species; however, this is a dangerous way of determination because in Limacea and Spondylidae certain ornamentation patterns are found which are similar to those on Pectinidae and the recognition of fragments could induce certain errors in this case. In the present species it seems possible that the very fragmentary specimens recorded as «Pecten icaunensis» from the Valanginian of Arzier, Vaud, (Switzerland) do in reality belong to Lima russillensis PICTET & CAMPICHE, 1870, or to Lima nicoleti PICTET & CAMPICHE, 1870 (this latter «species» only known from one incomplete specimen, could, according to PICTET & CAMPICHE, be identical with Pecten icaunensis). G. ROESSINGER, 1957, p. 102, considers that his almost complete specimens from the Valanginian from Arzier could be Limids instead of Pectinids, but he does not draw a definite conclusion. I have seen most of the specimens he studied in the Museum d'Histoire naturelle in Geneva, and amongst those some fragments very likely belong to a Limid, whereas some others have Pectinid characteristics; it does seem likely that two species with similar ornamentation are present. Chlamys ? icaunensis has a very restricted occurrence, which is unusual in Neocomian species. This could be due to the poor preservation of most Neocomian specimens, which very often are found as Steinkernen and such specimens of Chl? icaunensis would probably be classified as belonging to Chl. goldfussi (DESHAYES). When the ornamentation is present it is easy to recognize Chl? icaunensis; without it it is impossible to differentiate the specimens from those of Chl. goldfussi. Generic attribution:
The auricles of Pecten icaunensis COTTEAU, 1854 (p. 115 non 110) have never been seen satisfactorily; the general shape of the species is similar to that generally found in Chlamys species, but as long as the species is not better known it is preferable to leave the attribution as uncertain.
Stratigraphical and geographical distribution
Valanginian: SWITZERLAND:
Arzier, Vaud (Mus. Gen. orig. DE LORIOL, 1868, pI. 4, fig. 6, Mus. Laus.) Barremian: SWITZERLAND: Mormont, Vaud (Mus. Laus.) Neocomian (without specifications): FRANCE: Bernouil, Yonne (Mus. Gen.) Bettancourt, Haute-Marne (Mus. Gen.) Gy-I'Evêque, Yonne (B., Mus. Gen., Mus. Laus.) Marolles, Aube (Mus. Gen.) Thieffrain, Aube (Mus. Gen.) SWITZERLAND: Concise, Neuchatel (Univ. Neuch.) Aptian: SWITZERLAND: La Presta, Neuchâtel (Mus. Gen.)» 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. 54-56]
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Chlamys? icaunensis (G. Cotteau, 1854); A. V. Dhondt, 1973, Systematic revision of the Chlamydinae (Pectinidae, Bivalvia, Mollusca) of the European Cretaceous. Part 3: Chlamys and Mimachlamys, plate 9, figures 1a, 1b.
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