Neithea gibbosa (Pulteney, 1813)
PULTENEY, R. 1813. Catalogues of the Birds, Shells, and some of the More rare Plants of Dorsetshire. 110 p., pls. 1-13. Printed by and for Nichols, Son, and Bentley, London. [p. 107, pl. of Melbury Fossils, fig. 2]
1813 Pecten gibbosus Pulteney, 1813
1813 Pecten planatus Pulteney, 1813
1814 Pecten quadricostata J. Sowerby, 1814
1853 Janira faucignyana Pictet & Roux, 1853
1813 Pecten planatus Pulteney, 1813
1814 Pecten quadricostata J. Sowerby, 1814
1853 Janira faucignyana Pictet & Roux, 1853
R. Pulteney, 1913, plate Melbury fossils.
|
«A large Pecten, which may perhaps be thus defined:
Pecten (gibbosus), testa inaequivalvi, aequilatera, auriculata, fornice gibba, costis (21) rotundatis laevibus, quartis fornicis radiis, reliquis crassioribus. The convex valve, or formix, is very highly gibbous: the lower valve plain, or rather concave, and the ribs nearly equal in thickness. It is one of the most rare of the Melbury fossils. The character respecting every fourth rib holds in all the specimens I have seen. This is one of the largest size. I am not acquainted with any figure of this fossil in any author I have seen, nor with any recent shell corresponding to it.» RICHARD PULTENEY, 1813
|
«Description. Medium-sized to large species with large, unequal auricles; six well-developed principal ribs and generally only three intercalaries. Shell shape and ornament similar to N. regularis, but right valve less convex, umbo wider and rib intervals flatter.
Remarks. Distinguished in general from N. quinquecostata by its coarser appearance and much larger size, while all the ribs seem to be of the same type and its large auricles are closer to the hinge line. Exceptionally, specimens found in the Upper Greensand at Blackdown, Devon, have a greater number of intercalary ribs than normal. Occurrence. Albian-Cenomanian; Devon, Dorset and Wiltshire.» CLEEVELY, R. J. & N. J. MORRIS. 2002. Introduction to molluscs and bivalves. In A. B. Smith & D. J. Batten (Eds.): Fossils of the Chalk, 99-160. The Paleontological Association. London. [p. 128]
|
Neithea (?Neithea) gibbosa (Pulteney); R. J. Cleevely & N. J. Morris, 2002, Introduction to molluscs and bivalves, plate 21, figure 11.
|
Discussion:
«Variability. — In principle the number of intercalary ribs is 3; however, it happens that some principal intervals bear 4, instead of 3, intercalaries, and this mostly, in the outer intervals. More rarely an extra intercalary rib is present in one of the median intervals; this explains specimens with a total of 24 ribs. These specimens seem to be exceptional and I have seen them only from Blackdown (England).
The number of riblets on the areas varies and it is very difficult to define it; those riblets are very easily worn off and in many cases the areas are not wholly disengaged from the matrix. On those specimens where they could be counted, the same number was present on anterior and posterior areas: between 2 and 6. The differences which are to be seen in auricleshape depend largely on the size of the individuals, thus probably on the growth stage. On smaller (younger) shells, the auricles are relatively larger in comparison to the shell than on larger (older) shells. Synonymy. — Pecten gibbosus PULTENEY was published in a paper which had been completely lost for Palaeontology. The name which has been used for 150 years was Pecten quadricostatus SOWERBY, which is a few years younger than PULTENEY's name. L. R. COX, 1940 took PULTENEY's paper and the name Pecten gibbosus out of oblivion.
The advantage of using PULTENEY's name is that the difference between Neithea quadricostata (SOWERBY) [ = N. gibbosa (PULTENEY)] and N. quadricostata (D'ORBIGNY) [ = N. regularis (SCHLOTHEIM)] becomes clearly established. Indeed, since GOLDFUSS, there has been a very profound confusion between N. quadricostata (SOWERBY) from the Apdan-Cenomanian and the species with 3 intercalary ribs, from the Upper Cretaceous [N. regularis (SCHLOTHEIM)]. GOLDFUSS gave the name Pecten quadricostatus to both. D'ORBIGNY made things even more confused by describing as Janira quadricostata a very obvious N. regularis (for more details see above sub N. regularis). BRIART et CORNET, 1868, PICTET et CAMPICHE, 1871 corrected this mistake and WOODS description and figures definitely put an end to it. Differentiation. — The very early confusion between N. gibbosa and N. regularis is easy to understand, if one remembers that it is very rare to find well preserved fossils and that the differential characterisdcs between the 2 species are only clearly visible on very well preserved specimens: both areas and auricles must be visible.
On less well preserved specimens a difference can still be noted by the less convex right valve of N. gibbosa, by its wider umbo, its flatter intervals, but these characteristics are difficult to interpret without a large series of comparative material. The other Neithea-species may be differentiated from N. gibbosa by : — the areas, beak and auricles for N. coquandi (PÉRON); — the number of intercalary ribs for N. alpina (D'ORBIGNY); — the areas and shape of the shell and equal ribs for N. hispanica (D'ORBIGNY); — the wide beak and the number of ribs for N. striatocostata (GOLDFUSS) and N. sexcostata (WOODWARD); — the unequal ribs for N. fleuriausiana (D'ORBIGNY), though in this case the shape is similar. Neithea royeriana (D'ORBIGNY, 1850) from the Aptian of Vassy: «Espèce voisine par le nombre de ses côtes du J. quadricostata, mais avec plus d'inégalité dans leur largeur et dans leur disposition». This description could point to a N. gibbosa. The type specimen according to D'ORBIGNY's register should have the nº 5678 A. This specimen I could not find during my stay at the Muséum. I did find 5678, but this individual is from Pont Varin (Haute-Marne) and thus cannot be used as a type, because it was not mentioned in the original description. Besides it has such a narrow beak that it cannot be confused with N. gibbosa. N. attockensis L. R. COX, 1935 (pp. 20 and 21, pl. 2, figs. 17-20) from the Albian of Attock district, India shows a strong similarity to N. gibbosa; the specimens of the former species are however much smaller and seem to be more convex than those of the latter, and unfortunately the preservation state is poor, so that no definite conclusion can be reached without the original material.» 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. 57, 58]
|
Neithea (Neithea?) gibbosa
(R. Pulteney, 1813); A. V. Dhondt, 1973, Systematic revision of the subfamily Neitheinae of the European Cretaceus, plate 2, figure 3. |