"Chlamys" martiniana (d'Orbigny, 1850)
ORBIGNY, A, D'. 1850. Prodrome de Paléontologie stratigraphique universelle des animaux mollusques et rayonnés. Deuxième Volume. 427 pp. Victor Masson. Paris. [p. 107]
1850 Pecten martinianus Orbigny, 1850
1866 Pecten urgonensis Loriol, 1867
1869 Pecten landeronense Loriol in Loriol & Gilliéron, 1869
1850 Pecten martinianus Orbigny, 1850
1866 Pecten urgonensis Loriol, 1867
1869 Pecten landeronense Loriol in Loriol & Gilliéron, 1869
Chlamys urgonensis de Loriol; M. Cossmann, 1907, Description des gastropodes et pélécypodes. In E. Pellat & M. Cossmann, 1907, Le barrêmien supérieur à faciès urgonien de Brouzet-lez-Alais (Gard), plate 6, figure 5.
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«*731. Martinianus, d'Orb., 1847. Espèce déprimée, pourvue de vingt côtes rayonnantes simples, espacées. Martigues, couches à Caprotina.»
ALCIDE D'ORBIGNY, 1850
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«Diagnosis. — Medium-sized Chlamys? species with 14 to 24 straight rounded, mostly undivided, ribs and rather broad intercostal intervals. The shell is completely covered with concentric striae.
The disc is flattened; the ribs are rounded and sometimes subdivided on both valves and the intercostal intervals are as wide as the ribs. Discs and auricles are covered with numerous closely set concentric striae which can become concentric riblets, and, when crossing the ribs, sometimes form a small transverse ridge. Near the umbo, these concentric processes are well developed and the disc surface has a trellis-like appearance. On the areas near the side margins the concentric striae become oblique. The right valve sometimes has subdivided ribs which can separate and thus increase the ribnumber. Anterior auricle : winglike, with a deep byssal sinus, covered with concentric striae which follow the sinus and of which a major number have become riblets. Posterior auricle small, obtuse-angled and covered with the continuation of the concentric striae which follow the outer margin. The left valve has a similar ornamentation but when ribs are added it is by intercalation. Anterior auricle large and with a very shallow byssal sinus, covered with radial and concentric striae which give a trellislike appearance. Posterior auricle small and obtuse-angled but covered with a similar ornamentation. Discussion
Variability:
The ribnumber varies greatly for a species with so few ribs; its is however, impossible to divide the specimens into two specific groups as in DE LORIOL. In fact, the variation lies between 15 and 21, which is a more usual distribution; the large groupe of specimens from Mormont gives a normal distribution. Abnormally high ribnumbers are occasioned by the rare increase in ribnumber on the discs. Synonymy:
DE LORIOL's two «species» differ in so few characteristics that already PICTET & CAMPICHE (p. 187) wrote: «Ce peigne (P. landeronensis) est certainement tres-voisin de l'urgonensis, et quelques echantillons intermediaires nous ont quelquefois rendu leur separation difficile...». I have tried to separate the two groups but they form a compact block (14 R 1 sp., 15 R: 9 sp., 16 R: 23 sp., 17 R: 19 sp., 18 R: 13 sp., 19 R: 8 sp., 20 R: 10 sp., 21 R: 6 sp., 24 R: 2 sp.). This asymmetrical distribution is due to the occasional increase of ribs. P. martinianus was only described in the Prodrome and thus probably escaped DE LORIOL's notice. PICTET & CAMPICHE considered it to be «insuffisamment decrite ». Differentiation:
From the other Lower Cretaceous Chlamys ? species C.? martiniana can be differentiated on the following points : — C.? archiaciana (D'ORBIGNY) has a similar ribnumber on some specimens, but then their distribution is irregular. — C.? goldfussi (sensu D'ORBIGNY) is generally larger, has tripartite ribs on the right valve and fairly large scales on the ribs of both valves. — C.? icaunensis (COTTEAU) has a particular ornamentation. -- C.? elongata (LAMARCK) has tripartite ribs. Generic attribution:
Pecten martinianus D'ORBIGNY, 1850, has the disc and auricle shape, ribdistribution and number typical for Chlamys ROEDING. The thimble microsculpture has not been seen; it is probably worn off. Hence it seems preferable to name Pecten martinianus, Chlamys? martiniana (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. 40, 41]
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