Neithea sexangularis (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. 648, pl. 448, figs. 5-8]
1847 Janira sexangularis Orbigny, 1847
1897 Vola quinqueangularis Noetling, 1897
1897 Vola quinqueangularis Noetling, 1897
A. d'Orbigny, 1844-1847,
plate 448. |
«J. testâ trigonâ , concentricè subtilissimè striatâ; valvâ inferiore convexâ, incurvatâ, radiatim 6-angulatâ, angulis subacutis, bicostatis; interstitiis sulcis latis, excavatis, longitudinaliter striato-costulatis; auriculis inaequalibus, acutis, radiatim costulatis.
Dimensions. Largeur, 77 millim. — Par rapport à la largeur: longueur, 82/100; épaisseur, 17/100; longueur de la facette des oreilles, 38/100. — Angle apicial , sans les oreilles, 92°.
Coquille trigone, flabelliforme, plus longue que large, marquée, en travers, de très-légères stries d'accroissement. Valve inférieure très-bombée, fortement recourbée au sommet, pourvue de six angles très-saillans, anguleux , formés de deux petites côtes entre lesquelles sont des parties très-évidées, creuses, ornées d'un grand nombre de petites côtes ou de stries longitudinales peu prononcées. La partie externe des angles externes est striée en long. Oreilles inégales, anguleuses, ornées de petites côtes rayonnantes.
Rapports et différences. Cette espèce est voisine de forme du J. Truellei, mais elle s'en distingue spécifiquement par ses angles plus saillans, pourvus de deux au lieu d'une côte, par un grand nombre de petites côtes ou de stries intermédiaires au lieu de cinq côtes , enfin par un aspect tout différent. Localité. Elle est propre à l'étage sénonien ou craie supérieure du bassin pyrénéen. Elle a été recueillie à Pons, à Coze, à Mirambeau (Charente-Inférieure ), par M. d'Archiac et par moi. Explication des figures, PI. 448, fig. 5. Coquille de grandeur naturelle. De ma collection. Fig. 6. La même, vue de profil. Fig. 7. Une côte grossie. Fig. 8. Profil de la même.» ALCIDE D'ORBIGNY, 1847
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«Material: One small specimen (B128: H = 19.5 mm; L = 17.9 mm.) from Pinei, Lago di S. Croce.
Discussion: Though somewhat distorted, the small specimen from Pinei shows typical characteristics of N. (N.) sexangularis: the wide angular, deeply subdivided principal ribs, the deep intercostal intervals which here seem smooth. As stated previously (Dhondt, 1985), it could be that N (N.) sexangularis represents only an extreme variation of N (N.) striatocostata (Goldfuss, 1833) but until transitions between the two are found it is preferable to describe them as distinct taxa.
Distribution: Recorded from Coniacian to Campanian (?Maastrichtian): SW France (Aquitaine), Spain, Germany (Bavarian Alps), NE Italy (eastern Venetian Prealps), ?India.»
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. 196]
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Neithea (Neithea) sexangularis (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 4.
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«Discussion
— The material of Neithea sexangularis and N. striatocostata collected on the A 10 exposures is relatively poorly preserved. Nevertheless it shows that, contrary to my previous statements (Dhondt, 1973a, b, 1983), N. sexangularis cannot be accepted as a species: it is only an extreme variation of N. striatocostata. However, this extreme variation is not found in all strata in which N. striatocostata is known to occur, but is limited to the Campanian and geographically it seems restricted to warm temperate and northern Tethys seas. I have mentioned N. sexangularis as a separate taxon to draw attention to this change in variability.» DHONDT, A. V. 1985. Late Cretaceous bivalves from the A 10 exposures in Northern Aquitaine. Cretaceous Research, 6 (1-2): 33-74, figs. 1-6. [p. 42, 43]
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Neithea sexangularis (d’Orbigny, 1847); A. Dhondt, 1985, Late Cretaceous bivalves from the A 10 exposures in Northern Aquitaine, figure 2d.
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Location and designation of type-specimens. — In the Muséum d'Histoire natureile, in Paris: coll. D'ORBIGNY, 7620, chosen by J. ROGER, 1956.
Vola quinqueangularis NOETLING : in the Geological Survey coll. of India. Locus typicus. — Pons (chosen by ROGER) (Charente-Maritime) France.
Neithea quinqueangularis: Dès valley. Mari Hills, Baluchistan (West-Pakistan). Stratum typicum. — Etage sénonien ou craie supérieure du bassin pyrénéen (Senonian-according to several authors: Upper Senonian ( = Campanian).
Neithea quinqueangularis: Dès valley, Upper Cretaceous, Maëstrichtian. (...)
Diagnosis. — Medium-sized Neithea-species with 6 very prominent principal ribs which result in a strongly digitated pallial margin. On the intervals and on the principal ribs there are numerous, not very salient and very narrow, riblets.
Right valve: broad and not very convex; auricles are probably equal, but I am not certain of it because I have not seen any specimen with wholly undamaged auricles. Left valve: flattened, if one can say so when the principal ribs are so salient; in shape it is more angular than the right valve; for this valve also I never saw complete auricles, but what I saw makes it probable that they are very small. Rib arrangement: rather plain, consisting of 6 principal ribs which have the same width as the intervals, and both are covered with riblets, which vary in number and width; this could be due to the preservation state. On some specimens the general aspect is smooth: the riblets have then only reached a striae development, and do not project above the shell-surface. Discussion:
Variability. — Having seen relatively few specimens of this species the only variability I could notice is that in ornamentation and rib shape: the ribs are not always as salient nor the pallial margin as digitated as D'ORBIGNY's figures lead one to assume. The number of riblets varies greatly, but they are always evenly distributed on the principal ribs and in the intervals and this makes it difficult to decide where the principal rib ends and the interval begins.
Synonymy. — The description and figures in D'ORBIGNY are almost correct, but on figure 5 he exaggerated the angularity: the difference in length in the middle and outer ribs is more pronounced than on his drawing and because of this, the pallial margin is less angular. On the photographs of the type-specimens given by J. ROGER this is cleariy visible.
The type-specimens of O. REIS in Munich are lost; from the same localities from which he mentioned N. sexangularis new material has been collected: in those new specimens from the Hachauer Schichten nothing is ascribable to N. sexangularis; some specimens of N. sexcostata (WOODWARD) are present so it could be, but it cannot be proved, that REIS' material really belonged to N. sexcostata. N. quinqueangularis (NOETLING) has, on the specimens figured by the author, only 5 principal ribs: I have the impression that the figured specimens are imperfect and that complete they probably had an extra rib. Here, only the original material, could allow a decisive conclusion to be reached. If NOETLING's species were proven identical with N. sexangularis (D'ORBIGNY), it would be an important stratigraphical and paleogeographical point: until now D'ORBIGNY's species is only known to occur in strata of Campanian-Maastrichtian age of S.W. France. The species from Baluchistan comes from strata attributed to different formations, but which are all supposedly of Senonian-Maastrichtian age. The other Pectinidae mentioned by NOETLING do not give a precise stratigraphical indication: Vola quadricostata [ = N. (Neithea) regularis (SCHLOTHEIM)] occurs from the Upper-Cenomanian to the Upper-Maastrichtian and Pecten dujardini ROEMER [ = Lyropecten (Aequipecten) ternatus (MUENSTER in GOLDFUSS, 1833)] has a similar stratigraphical distribution. It is typical that both species are also found in the Charente. The exact systematic position of N. sexangularis is difficult to assess: the special shape makes its relation to other species indistinct. Some specimens as f.i. fig. 4 of J. ROGER, nº 46, however, are comparable to worn individuals of N. striatocostata (MUENSTER in GOLDFUSS). In this particular specimen the only real distinctive characteristic is the large number of riblets. Other individuals with the ornamentation described and figured by D'ORBIGNY make any confusion impossible. They are the extreme variation in this species. It seems likely that N. sexangularis is closely related to and perhaps evolved from N. striatocostata. Differentiation. — Neithea sexangularis is differentiated from :
— N. striatocostata (MUENSTER in GOLDFUSS) by a more digitated pallial margin and by far more numerous riblets and probably by having smaller auricles; — N. sexcostata (WOODWARD) by a much broader shell (U.P.D. < W.) , by a wider A.A., relatively smaller auricles and by more digitated pallial margin; — N. quinquecostata (SOWERBY) by the more salient principal ribs and the more numerous, but less developed riblets; — N. atava (ROEMER) by narrower, less prominent principal ribs and more regularly distributed riblets; — N. notabilis (MUENSTER in GOLDFUSS) by the symmetrical shell and by the small, equal auricles; — N. gibbosa (PULTENEY), N. coquandi (PERON), N. regularis (SCHLOTHEIM), N. alpina (D'ORBIGNY), N. dilatata (D'ORBIGNY), N. dutrugei (COQUAND) by the absence of intercalary ribs.» 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. 53-55]
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Neithea (Neithea) sexangularis (d'Orbigny); A. V. Dhondt, 1973, Systematic revision of the subfamily Neitheinae of the European Cretaceus, plate 3, figure 3.
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