Dhondtichlamys subinflexus (Dhondt, 1972)
DHONDT, A. V. 1972. Systematic revision of the
Chlamydinae (Pectinidae, Bivalvia, Mollusca) of the European Cretaceous. Part
2: Lyropecten. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, 48 (7): 1-81, pls. 1-3. [p. 32]
1842 Pecten inflexus Hagenow, 1842
1972 Lyropecten (Aequipecten) subinflexus Dhondt, 1972 [nomen novum pro Pecten inflexus von Hagenow, 1842]
1972 Lyropecten (Aequipecten) subinflexus Dhondt, 1972 [nomen novum pro Pecten inflexus von Hagenow, 1842]
Pecten inflexus v. Hegenow; D. Wolansky, 1932, Die Cephalopoden und Lamellibranchiaten der Ober-Kreide Pommern mit einem Abriß der Stratigraphie und Palaeogeographie des Südbaltikums vom Wealden bis zum Senon, plate 2, figures 18, 19.
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«. 1842 – Pecten inflexus nobis F. VON HAGENOW, p. 551.
(1849) – Pecten inflexus Hag. H.G. BRONN, p. 925 v . 1853 – Pecten inflexus Hag. ? C. PUGGARD, p. 16, f. 29 (1871) – Pecten inflexus Hagenow F. STOLICKA, p. 429. v . 1902 – Pecten inflexus von Hegenow p.p. J. P. J. RAVN, p. 83, pl. 1, f. 8 (non 10) 1921 – Pecten (Chlamys) inflexus v. Hag. J. P. J. RAVN, p. 20. ? 1925 – Pecten cf. finflexus v. Hag. R. POTONIÉ, p. 618. 1930 – Pecten (Chlamys) inflexus v. Hagenow R. HÄGG, p. 39 v. 1932 – Pecten (Chlamys) inflexus Hagenow D. WOLANSKY, p. 15, pl. 2, f. 18-19 ? 1940 – Chlamys inflexus v. Hagenow (sic) V. TZANKOV, p. 486, pl. 6, f. 4. ? 1941 – Pecten (Chlamys) inflexus v. Hag. E. STOLL, p. 93, pl. 2, f. 5. ? 1945 – Pecten inflexus v. Hag. A. JESSEN, p. 13. 1946 – Pecten (Chlamys) inflexus v. Hagenow J. P. J. RAVN, p. 24. 1964 – Pecten (Chlamys) inflexus v. Hag. R. GIERS, p. 233. non 1918 Pecten inflexus (POLI) in LAMARCK, p. 173.
non 1902 Pecten inflexus J. P. J. RAVN, pl. 1, f. 10. non 1923 Pecten (Chlamys) inflexus A. JESSEN and H. ØDUM, p. 35, pl. 2, f. 5. non 1926 Pecten (Chlamys) inflexus H. ØDUM, p. 180. = Lyropecten (Aequipecten) acuteplicatus (ALTH, 1850). Derivatio nominis
Pecten inflexus being pre-employed, I replace it by subinflexus.
Location of type-specimens
VON HAGENOW'S collection was destroyed in the Museum of Szczecin during the Second World War; only those specimens which were on loan during that period are still extant.
Stratum typicum: Kreide (here : Lower Maastrichtian). Locus typicus: Rügen (G. D. R.). Original description.
"Grösse und Gestalt wie bei der vorigen Art (7). Bei jungen Exemplaren: welche etwas 2/3 der Grösse erreicht haben, ist der Wirbel und der grösste Theil der Schaale glatt oder zart konzentrisch gestrichelt, und nur am unteren Rande zeigen sich Spuren kurzer Rippen. Hinter dem ersten, schon ziemlich stark aufliegenden Wachsthums-Absatze nehmen die Rippen an Stärke zu und haben mit den Zwischenräumen gleiche Breite. Ganz alte Exemplaren haben 3 bis 4 solcher Absätze, welche einander Ziegel-artig überlagern und deren letzter nach innen scharf umgekrämpf ist und der Schaale ein Napf-förmiges Ansehen gibt.
Die zuweilen dichotomirenden flachen Rippen strahlen geradlinig aus und sind, wie auch die Zwischenräume, konzentrisch fein gestrichtelt, letzte am deutlichsten. Am vorderen und hinteren Rande ist bei ganz alten Exemplaren noch eine diagonale Streifung bemerkbar; die ungleichen Ohren sind wie der vorigen Art (7) gestaltet und schuppig gerippt." Additional description
Number of specimens studied: 67.
Senonian in Liineburg (G. F. R.) ... .... ... 2 Maastrichtian in Belgium ... ... ... ... ... ... 1 Maastrichtian in Denmark ... ... ... ... ... ... 43 Maastrichtian in Riigen (G. D. R.) ... ... ... ... 21 Measurements: U. P. D. varies from 4.5 mm to 12.3 mm (n = 27) W. varies from 4.3 mm to 12.0 mm (n = 25) A. A. varies from 86° to 105° (n = 19) Description Diagnosis. — Small Lyropecten (Aequipecten) species with 24 to 45 ribs, sometimes divided, but rarely well developed near the umbo; many specimens have growth ridges ("Absätze") and some have slight concentric ornamentation. The valves are rather flattened. The ornamentation consists of ribs which are very weakly developed near the umbo; indeed, on some specimens the umbonal part appears smooth. Near the pallial margin they are more developed but they are never very prominent. The intercostal grooves are narrow. The auricles are unequal on both valves; on the right valves the anterior one is elongated and winglike. It bears radial riblets. The posterior auricle is much smaller and acute-angled. On the left valve the anterior auricle is acute angled and bears radial riblets; the posterior one is as on the right valve. Discussion
Synonymy and variability:
The State of preservation of the different specimens makes the counting of the ribs fairly difficult; the "Absätze" are not a specific characteristic; this type of growth interruption is found in species from very fine chalky sediments: L. (A) campaniensis (D'ORBIGNY), L. (A.) sarumensis (WOODS), Mimachlamys cretosa (DEFRANCE), Mimachlamys mantelliana (D'ORBIGNY), Neithea (Neithea) sexcostata (WOODWARD) and it is probably due to environment rather than to specific factors. The original diagnosis by VON HAGENOW is explicit but does not indicate rib-numbers. This probably explains the confusion which exists since RAVN, though VON HAGENOW himself must not have been very certain either: in the University of Greifswald a specimen labelled by him is "Pecten inflexus" but in the von Humboldt University another specimen labelled by VON HAGENOW as Pecten inflexus is in fact a L. (A) subaratus (NILSSON). RAVN, 1902, and many authors after him describe as Pecten inflexus specimens belonging to L. (A.) subinflexus and to L. (A) acuteplicatus (ALTH). TROELSEN, 1937, in his division of the "Skrivekridt" used 3 "varieties" of Pecten inflexus as index fossils for his zones: Pecten inflexus var. moenensis indicates zone I and II; P. inflexus var. aalborgensis indicates zone I, II, IlIa; P. inflexus var. stevnensis indicates zone IlIb and IV. TROELSEN's "varieties" remained nomina nuda. I found some specimens in the Mineralogisk Museum in Copenhagen which had been labelled by him and in Prof. ROSENKRANTZ's colI. there are also a few specimens with TROELSEN-labels. By counting the ribs of all the specimens I came to the conclusion that it is impossible to separate var. moenensis and aalborgensis. They are normal L. (A) subinflexus specimens as described above. The specimens of var. stevnensis are different and belong to L. (A) acuteplicatus (ALTH). It seems to be true that there is a stratigraphic discrepancy between both species: L. (A) subinflexus occurs in strata which are older than those from which L. (A) acuteplicatus has been recorded. Chlamys inflexus in V. TZANKOV, 1940, is unfortunately lost. Consequently, it is impossible to be sure that the attribution was correct. Generic attribution: Pecten inflexus VON HAGENOW non POLl in LAMARCK has the auricle shape, ribstructure, orbicular disc-shape known for Pecten opercularis (LINNAEUS, 1758) type-species of Aequipecten; its correct name thus becomes Lyropecten (Aequipecten) subinflexus nom. nov. Stratigraphical and geographical distribution
Senonian: G. F. R.:
Lüneburg (B.) Maastrichtian: BELGIUM - THE NETHERLANDS: Sint Pietersberg (I.R.Sc.N.B.) DENMARK: Bjerre Thy (KO.) Gudumsholm (KO.) Hillerslev (KO.) Hundevangsklint (KO.) Møen (KO.) Nörre Dump (KO.) Skovbakken, Aalborg (KO.) Stevns Klint (KO.) G.D. R. : Rügen (GR.)» ANNIE VALÉRIE DHONDT, 1972
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