Euthymipecten Dhondt & Dieni 1988
DHONDT, A. V. & I. DIENI. 1988. Early Cretaceous bivalves of eastern Sardinia. Memorie di Scienze Geologiche, 40: 1-97, pls. 1-13, text-figs. 1-25. [p. 30]
«Genus Euthymipecten nov. gen.
Type species: Pecten Astierianus D'ORBIGNY, 1850.
Derivation of name: Euthymi and pecten; PICTET (1867) gave the first illustration of the type species under the name Pecten Euthymi.
Diagnosis: Large, suborbicular, compressed, nearly equivalve and almost equilateral pectinid. Right valve: slightly more convex than left valve; ornamentation consists of broad radial primary ribs, with intercalary irregular secondary and sometimes tertiary ribs; auricles unequal; anterior auricle elongated and with byssal notch; posterior auricle narrowly triangular. Left valve: generally only covered by narrow primary ribs; both auricles narrowly triangular. Shell relatively thin.
Discussion: Cretaceous pectinid genus, probably belonging to the subfamily Chlamydinae VON TEPPNER, 1922 because of the byssal notch.
Similar Mesozoic pectinid genera differ in some characteristics: — Jurassic Pseudopecten BAYLE, 1878 superficially seems to have the same disc shape, but the rib arrangement is more regular and the shell is much heavier; — Eopecten DOUVILLÉ, 1897 [ = Velata QUENSTEDT, 1856 (non GRIFFITH and PIDGEON, 1834) = Velopecten PHILIPPI, 1899] is attached by the right valve but the ornamentation of both valves can be compared with Euthymipecten. In Eopecten the rib pattern is generally more intricate and the byssal notch is much more developed and functional at all stages. From other Early Cretaceous pectinid genera Euthymipecten can be distinguished as follows: — from Chlamys ROEDING, 1798 and Mimachlamys IREDALE, 1929 by the relatively smaller and more equal elongated auricles, by the less heavy shell and the more orbicular shape; — from Camptonectes AGASSIZ in MEEK, 1864 by the shallower byssal notch, by the less heavy shell, by the presence of developed radial rib ornamentation; — from Propeamussium DE GREGORIO, 1884 by the absence of internal ribs, and by the much larger shell and different shell structure; — from Neithea DROUET, 1825 by the almost equivalve shell and the regular ribpattern; — from Entolium MEEK, 1865 by the presence of a byssal notch and of radial ornamentation; — from Aequipecten FISCHER, 1887 (= Microchlamys SOBETSKI, 1977) by the absence of a functional byssal notch in adult stages and the generally larger size; —from Merklinia SOBETSKI, 1960 by the much less intricate radial ornamentation, the relatively less convex valves, the presence of far fewer spines; — from Lyriochlamys SOBETSKI, 1977 by the orbicular shape, the relatively small byssal notch and the radial ribs of varying order (Lyriochlamys is not clearly defined; the species which SOBETSKI listed as belonging to it do not seem to have much in common and some are only known as poorly preserved internal moulds. Therefore we compare Euthymipecten with the well known type species of Lyriochlamys: Pecten fissicosta ETHERIDGE, 1881 from the English Cenomanian). Species included: the type species, Pecten Astierianus D'ORBIGNY, 1850 (see further), and Pecten Beaveri SOWERBY, 1817 from the Albian-Cenomanian. Both species have a relatively wide geographic distribution, but are restricted ecologically to fine grained deposits. No other species has been found which can be included in this new genus.
Age and geographic distribution: Euthymipecten seems to be restricted to the Cretaceous and possibly it does not extend beyond the Cenomanian. Geographically it occurs mainly in Temperate climatic zones, but generally in fine-grained deposits such as Gault clays. It represents a group of pectinids wr.tich lived not in littoral waters, but in somewhat deeper seas.»
ANNIE VALÉRIE DHONDT & IGINIO DIENI, 1988
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Pecten Euthymi Pictet; F.-J. Pictet, 1867, Études paléontologiques sur la Faune a Terebratula diphyoides de Berrias (Ardèche), plate 21.
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