Neithea fleuriausiana (d'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. 631, pl. 443]
1847 Janira fleuriausiana Orbigny, 1847
1892 Neithea acuticostata Futterer, 1892
1900 Janira lapparenti Choffat, 1900
1968 Neithea (Neithella?) rotundata Freneix & Lefèvre, 1968
1892 Neithea acuticostata Futterer, 1892
1900 Janira lapparenti Choffat, 1900
1968 Neithea (Neithella?) rotundata Freneix & Lefèvre, 1968
A. d'Orbigny, 1844-1847, plate 433.
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«J. testâ ovatâ, depressâ; valvâ superiore convexo-planâ, radiatim sex-angulato-costatâ; costis inaequalibus, multicostulatis; interstitïis sulcis latis, excavatis (medio), decem costulatis; valvâ inferiore concavâ; radiatim 6-angulatâ, angulis convexis, 4-costulatis; interstitiis sulcis latis, excavatis, medio decem inaequaliter costulatis; auriculis magnis, inaequalibus, radiatim inaequaliter costulatis.
Dimensions. Longueur, 150 millim.— Par lapport à la longueur: largeur, 79/100, épaisseur, 33/100; longueur de la facette des oreillettes, 18/100.— Angle apicial , sans les oreillettes, 104°.
Coquille ovale, plus longue que large, déprimée dans son ensemble. Valve supérieure légèrement convexe, ornée de six saillies rayonnantes, inégales, marquées de côtes longitudinales inégales, entre lesquelles sont autant de larges sillons légèrement excavés. Valve inférieure assez convexe, bombée, pourvue de six côtes ruyonnantes, formées, chacune, de quatre petites côtes très-inégales. Enire chaque côte sont de très-larges sillons excavés , poarvus d'un grand nombre de côtes rayonnantes, inégales. Le sillon du milieu en offre une dizaine très-inégales, parmi lesquelles on en distingue une médiane double. Elles sont séparées par d'étroits sillons. Les oreilles sont grandes, inégales, couvertes d'un grand nombre de côtes rayonnantes, très-inégales entre elles.
Rapports et différences. Cette espèce, voisine, par ses nombreuses côtes, du Janira striaticostatus, s'en distingue par sa forme plus longue que large, tout-à-fait différente, par ses côtes autrement disposées, par sa valve supérieure un peu convexe, et enfin par tous ses détails d'ornement et de forme. Localité. Elle forme un horizon particulier à la partie la plus inférieure de l'étage turonien ou de la craie chloritée, avec les Caprina bipartita et les Radiolites foliacea. Elle a été recueillie par moi à l'île d'Aix, à l'île Madame (Charente-Inférieure), à Saint-Trojan, près de Cognac, et aux environs d'Angoulème (Charente). Explication des figures. Pl. 443, fig. 1. Coquille, vue en dessous, réduite d'un tiers. De ma collection. Fig. 2. La même, vue de profil.» ALCIDE D'ORBIGNY, 1847
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«Material:
- From Col dei Schiosi: external mould of an incomplete left valve (BI81: H > 56 mm); a decorticated right valve (B179) is tentatively also assigned to the species under discussion. - From Bocca di Crosis near Tarcento (Udine, Friuli): one small right valve (IGF 3090E). - From (?) Monte di Medea, Cormons, Udine: one large right valve (MSNT 10823, colI. Renzi). - From Aurisina, Trieste: one bivalved specimen (MSNT 11829) and one right valve (MGB/Fr 3). - From Monrupino (= Repentabor), Trieste: about 25 usually bivalved and generally large specimens [MSNT 11830 and 11831, originals of Parona (1926); MSNT 11835-11840 and about 15 unregistered specimens, all from the Zolla quarry; MGB/Fr 4; DGP 26692]. - From Buzet (= Pinguente), Istria, Croatia: one right (?) valve (MSNT 11828). - From Pula (= Pola), Istria, Croatia: one distorted bivalved specimen (MB, colI. Ewald). Diagnosis: Large to very large, relatively not very inflated Neithea species, with a straight beak, very large auricles, and numerous irregularly distributed ribs, of which six are more strongly developed.
The specimens on which the value B has been measured have been flattened; therefore the original value in uncrushed specimens exceeded the measured quantity.
Discussion: The straight beak of Neithea (Neithea?) fleuriausiana results in a less convex right valve than that normally found in the nominal subgenus as shown by the type species Pecten aequicostatus Lamarck, 1819. Yet, the general aspect of the species is closer to Neithea, especially because of the ornamentation, than to any other Cretaceous pectinid genus.
The rib ornamentation can vary greatly. Some specimens have strongly subdivided ribs (primary and secondary), as in the N. (N.?) fleuriausiana specimen from the Ile Madame figured in Dhondt (1973 b, pI. 4, fig. 1). Others have less divided ribs, which look as if there are fewer ribs, such as can be seen on specimens from the Trieste area figured herein (PI. V, fig. 20; PI. VII, fig. 2). An extreme reduction in the rib number can be seen on the specimen from Monte di Medea which has only 14 ribs (PI. VII, fig. 4a). Likewise, relatively few ribs are found on N. acuticostata Futterer, 1892 which is based on an incomplete right valve said to have come from "Calloniche". The description and the figure of the specimen seem to indicate a close similarity with N. (N.?) fleuriausiana; the holotype and only specimen of the taxon was not found in the Museum fur Naturkunde in Berlin. Very likely the locality of origin of the specimen is Col dei Schiosi rather than" Calloniche". The description given by Dhondt (1973b) is accurate, but the synonymy is incorrect: N. (N.?) fleunausiana (= N. lapparenti), characterised by a straight beak and a fairly flat right valve, is herein considered as a separate taxon from N. (N.?) inconstans (Sharpe, 1850) [= N. stefanoi (Choffat, 1902)?] (see below), which has a more convex right valve with a slightly incurved beak. Both taxa are roughly coeval and specific for rudist formations. N. roemeri (Hill, 1893), from the Buda Limestone (Early Cenomanian, Austin, Texas), is very similar to N. stefanoi, and is also a species associated with rudists. N. zitteli in G. Boehm [1897, and in Marinelli (1897)] is based on a right and a left valve from Bocca di Crosis near Tarcento (Udine, Friuli), housed in the Museo di Geologia e Paleontologia, University of Florence (IGF 3090E). The small right valve belongs undoubtedly to a young N. (N.?) fleuriausiana specimen. Distribution: Neithea (N.?) fleuriausiana is sometimes found in mass occurrences in one bed. This is for example apparent in the Monrupino area (Trieste Karst), where numerous bivalved, very large and more or less flattened specimens occur together in what is a largely monospecific assemblage.
N. (N.?) fleuriausiana has only been recorded from Late Cenomanian rudist beds: Portugal, SW France (Ile Madame, Ile d'Aix, Angouleme), Italy (Friuli, Venezia Giulia and Abruzzo), Croatia (Istria, Dalmatia), western Slovenia, western Serbia, Greece, Libya (Text-fig. 5).» DHONDT, A. V. & I. DIENI. 1993. Non-rudistid bivalves from Late Cretaceous rudist limestones of NE Italy (Col di Schiosi and Lago di S. Croce areas). Memorie di Scienze Geologiche, 43: 165-241, pls. 1-20, text-figs. 1-18. [p. 191, 192]
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Neithea (Neithea?) fleuriausiana (d'Orbigny. 1847); A. Dhondt & I. Dieni, 1993, Non-rudistid bivalves from Late Cretaceous rudist limestones of NE Italy (Col di Schiosi and Lago di S. Croce areas), plate 5, figure 20; plate 7, figures 1-3, 4a, 4b.
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«Diagnosis. — Remarkable Neithea-species with almost straight beak, very large auricles especially on small (young) valves, an irregular distribution of intercalary ribs. Typical for Rudist bioherms and thus often very distorted and flattened specimens.
The beak, being almost straight, makes the right valve far less convex than in other Neithea-species. This results in the left valve being concave, flattened or even slightly convex. It could be that this variation depends on the substratum on which the organism lived. The rib distribution is very variable though the basis pattern is the same as in the other Neithea-species: 6 principal ribs which are strongly developed and salient above the shell surface. Between these principal ribs, and, on their sides, the number of intercalaries varies greatly because the numerous intercalaries do occasionally split. The number of intercalaries is not even stable in the intervals of one shell, e.g. the numbers of intercalary ribs counted at the pallial margin on the specimens of which measurements are given above (anterior-posterior): 4 / 6 / 9 / 5 / 4
6 / 1 0 / 9 / 7 / 4 6 / 9 / 9 / 7 / 4 5 / 5 / 7 / 10 / 4 (on the last speeimen the rib number at the anterior side is abnormally low, because it is slightly distorted).
The intercalaries arc more numerous in the middle of the shell than on the sides; this may be related to the intervals being wider in the middle too. The intercalaries vary not only in number, but also in development; some intercalaries almost reach the development of principal ribs. The auriculae are large and very unequal: on the right valve the anterior auricle has a hollowed lower margin; the posterior auricle is larger, it ends beyond half the apical line. Its hinge line is as long as half the width of the shell, and, in some cases it is even longer. On the left valve, the auricles are the reflected image of the right valve auricles: the anterior one here is the larger and the posterior one is the smaller, but it is not hollowed. The side-margin of the auricles is rectangular to the hinge-line, on small specimens, because the angle is acute; on larger specimens the auricles are rectangular and the side-margin is parallel with the U.P.D. of the shell. The areas and auricles are covered with close-set riblets which reach the same development as the intercalaries. Around the umbo these riblets are diverging; on the areas they are almost parallel with the last principal ribs; each next riblet is slightly displaced so that the last riblet on the auricle is parallel to the hingeline. Discussion:
Variability. — As stated in the additional description the shape of the principal and intercalary ribs is extremely variable: at one end of the variation series one finds specimens with 6 very salient principal ribs with a great number of intercalary ribs (which are difficult to count) much less developed than the principal ribs, at the other end there are fewer intercalary ribs which are almost as strongly developed as the principal ribs; thus in very extreme cases one sees specimens with almost equal ribs.
The size is very variable too; the measurements given above are on the low side; in Rudist bioherms individuals can reach very large sizes. Synonymy. — Neithea fleuriausiana (D'ORBIGNY) had been very well described, but, badly figured: the additions added for completing a poorly preserved specimen are not quite correct; on the drawing of the right valve the anterior auricle is larger than the posterior one, whereas in fact it is the other way round. The ornamentation is far less regular than drawn by D'ORBIGNY.
N. inconstans (SHARPE) and N. acuticostata FUTTERER are both forms with 19 almost equal ribs, thus the extreme case mentioned in the variability. Here the areas and auricles are exacdy as represented on the typical form by D'ORBIGNY. N. lapparenti (CHOFFAT) differs from N. fleuriausiana, according to CHOFFAT, by having much sharper ribs. From Ile Madame I have seen a specimen which has very sharp ribs too; but this is due partly to the preservation state and partly to the variability of the rib shape. N. stefanoi (CHOFFAT) is slightly more convex than the other forms and might, according to figure 3 b in CHOFFAT, even have an incurved beak; the auricles are otherwise proportioned. Without seeing the material I cannot decide whether the differences fall within the variation. Habitat. — The species is typical for Middle Cretaceous rudist-reefs. As all other «reef» organisms they are strongly adapted to their physical environment and this explains their somewhat irregular shapes and the great variability in their proportions. Limited to the Tethys «reefs».
Differentiation. — This species is exceptional among the Neithea-species. It differs from most other Neithea-species by its irregularity and by its not very pronounced convexity of right valves. It has a morphological similarity with N. deshayana (MATHERON) which could result from similar environment; they both lived in rudist reefs. Their auricles have similar forms, but the ribs structure cannot be compared because for N. deshayana this is practically unknown. It seems not impossible that both species might be closely related. Large specimens of N. atava (ROEMER) are sometimes slightly similar to N. fleuriausiana but they are never as flat and irregular as N. fleuriausiana and their auricles are much smaller.
Generic attribution. — J. ROGER expresses some doubts as to the generic position of Janira fleuriausiana. His doubts can be easily understood, because, indeed, the beak is not incurved and the right valve is not very convex. A specimen from Ile Madame (Charente-Maritime) kept in the Coll. K.U.L. shows clearly on its posterior auricle the sawlike striation at the hinge which according to DROUET's definition of the genus is the second generic characteristic. The auricles being unequal one cannot decide whether Janira fleuriausiana belongs to the subgenus Neithea as well. The correct name in the present state of knowledge thus becomes Neithea (Neithea ?) fleuriausiana (D'ORBIGNY, 1847).»
DHONDT, A. V. 1973. Systematic revision of the subfamily Neitheinae (Pectinidae, Bivavia, Mollusca) of the European Cretaceus. Mémoires du Institute Royal des Sciences Naturelles de Belgique, 176: 1-101, pls. 1-5. [p. 62, 63]
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Neithea (Neithea ?) fleuriausiana
(A. d'Orbigny, 1847); A. V. Dhondt, 1973, Systematic revision of the subfamily Neitheinae of the European Cretaceus, plate 4, figure 1. |