Pseudopecten equivalvis (J. Sowerby, 1816)
SOWERBY, J. & J. DE C. SOWERBY. 1812-1846. The Mineral Conchology of
Great Britain; or coloured figures and descriptions of those remains of
testaceous animals or shells. 7 vols., pls. 1-648 (and 2 bis). London. [vol. 2, p. 83, pl. 136, fig. 1]
1816 Pecten equivalvis J. Sowerby, 1816
1819 Pecten acuticosta Lamarck, 1819
1820 Pectinites priscus Schlotheim, 1820
1825 Pecten araneosus Defrance, 1825
1828 Pecten sublaevis Young & Bird, 1828
1828 Pecten major Young & Bird, 1828
1833 Pecten acutiradiatus Münster in Goldfuss, 1833
1833 Pecten costulatus Hartmann in Zieten, 1833
1836 Pecten acuticosta Roemer, 1836
1850 Pecten cephus Orbigny, 1850
1858 Pecten aequalis Quenstedt, 1856
1872 Pecten hinterhuberi Tietze, 1872
1881 Pecten caracolensis Steinmann, 1881
1884 Pecten dichotomus Simpson, 1884
1884 Pecten interstinctus Simpson, 1884
1884 Pecten rudis Simpson, 1884
1890 Pecten norigliensis Tauch, 1890
1895 Pecten johnstrupi Lundgren, 1895
1924 Chlamys mcconnelli McLearn, 1924
1935 Chlamys sendelbachensis Kühn, 1935
1936 Aequipecten maximiliani Kühn, 1936
1942 Aequipecten bierringi Rosenkrantz, 1942
1819 Pecten acuticosta Lamarck, 1819
1820 Pectinites priscus Schlotheim, 1820
1825 Pecten araneosus Defrance, 1825
1828 Pecten sublaevis Young & Bird, 1828
1828 Pecten major Young & Bird, 1828
1833 Pecten acutiradiatus Münster in Goldfuss, 1833
1833 Pecten costulatus Hartmann in Zieten, 1833
1836 Pecten acuticosta Roemer, 1836
1850 Pecten cephus Orbigny, 1850
1858 Pecten aequalis Quenstedt, 1856
1872 Pecten hinterhuberi Tietze, 1872
1881 Pecten caracolensis Steinmann, 1881
1884 Pecten dichotomus Simpson, 1884
1884 Pecten interstinctus Simpson, 1884
1884 Pecten rudis Simpson, 1884
1890 Pecten norigliensis Tauch, 1890
1895 Pecten johnstrupi Lundgren, 1895
1924 Chlamys mcconnelli McLearn, 1924
1935 Chlamys sendelbachensis Kühn, 1935
1936 Aequipecten maximiliani Kühn, 1936
1942 Aequipecten bierringi Rosenkrantz, 1942
J. Sowerby, 1816, plate 136.
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«SPEC. CHAR. Lenticular, with rounded diverging ribs and many acute concentric striae; valves equally convex, the lower one smoothest; ears equal.
THE ribs vary in proportion; they sometimes equal the space between them, but are generally less; they are rounded and the striae are more or less obliterated over them: the spaces between them are slightly concave. Pectens are generically described by Lamarck as inequivalve, wherefore, I suppose, he had not seen any otherwise; but the present species has both valves nearly, if not quite, equally gibbous: one valve being simply convex, the other having a trifling reversed undulation near the edge, and differing but little in the pattern. The auricles have not, as I have seen, been found perfect, they are, however, nearly so, and they then show an horizontal line on each side of the beak, with nearly perpendicular lineae or striae. I have one by favour of Dr. Sutton, which has nearly parallel lines with the hinge on the dexter auricle of the broader valve, with the broad costae. This species is commonly found from three to seven inches in diameter. Mr. Strangewayes, from whom I have received several specimens, observes, that they are characteristic of the coarse Limestone of Ilminster. I have had other specimens from near Lackington, by favour of Mr. Strangewayes, also from Farley gateway, Gloucestershire; Carrington, Oxfordshire; and from Dursley, Gloucestershire. I believe the species is found in various other parts of England, and I have a specimen from France.» JAMES SOWERBY, 1816
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«Description. Shell small to large in size, sub-ovate in outline with low disc flanks. Equilateral and equivalved, moderately convex, with left valve more convex. Shell ornamented with 16-20 ribs, which are angular in juvenile specimens but more rounded in adult specimens; space between the ribs greater than the ribs; commarginal lines indistinct. Ears not preserved; apical angle about 90°.
Remarks. Johnson (1984) emphasized that “Pecten” acuticosta Lamarck differs from “Pecten” equivalvis Sowerby in having sharper ribs as a consequence of abrasion; hence, this feature cannot be used as a criterion for species designation. “Pectinites” priscus Schlotheim was identified on a single specimen and this name was later often used for small specimens of Pseudopecten (P.) equivalvis. Johnson (1984) also mentioned the criteria on which he believes “P”. priscus Schlotheim should be assigned to P. (P.) equivalvis. With respect to Johnson’s (1984) extensive research on Jurassic pectinids, his opinion about the identity of the three species is herein accepted. Occurrence. Sinemurian and Pliensbachian of Senokos; Pliensbachian of Bogorodica, Rosomač, Pesača, Radejna, Mali Vrh, Velika Lukanja, and Rgotina.» RADULOVIĆ, B. 2013. Lower Jurassic bivalves of eastern Serbia. Beringeria, 43: 3-61, pls. 1-20. [p. 28]
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Pseudopecten (Pseudopecten) equivalvis (J. Sowerby, 1816); B. Radulović, 2013, Lower Jurassic bivalves of eastern Serbia, plate 8, figures 12-21; plate 9, figures 1, 2.
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«2. AMENDED DIAGNOSIS
Distinguished from Ps. (Ps.) dentatus and Ps. (Ps.) veyrasensis by the low disc flanks and curvilinear comarginal striae.
3. AMENDED DESCRIPTION
Disc sub-ovate, higher than long in juvenile, growing allometrically to become longer than high (text fig. 44) towards maximum height of 179 mm (BM 2662). Umbonal angle increasing at a decreasing rate (text fig. 45) to produce concave dorsal margins. Disc flanks low.
Equilateral, moderately convex, left valve slightly more convex than right. Intersinal distance greater in left valve than right but increasing at a slightly increasing rate in both valves (text figs. 46, 47). Large byssal notch in right valve becoming relatively smaller during ontogeny (text fig. 48). Auricles well demarcated from disc, moderate in size, anterior slightly larger than posterior. Both anterior and posterior hinge lengths increasing at an increasing rate (text figs. 50, 51). Anterior auricle height increasing at a decreasing rate (text fig. 49). All auricles meeting hinge line at approximately 90°. Anterior auricle of right valve meeting disc at approximately 90°, other auricles meeting disc at an acute angle. All auricles ornamented with comarginal striae, anterior auricles also bearing 2-3 fine radial costae. Both valves ornamented with between 16 and 27, most commonly 22, radial plicae (text fig. 52). Plicae angular and often wider than sulei in juveniles but becoming more rounded and narrower than sulci later in ontogeny (PI. 1, Fig. 8). Plicae poorly defined at anterior dorsal and posterior dorsal margins of juveniles. Both plicae and sulci bearing fine radial striae and crossed by closely spaced curvilinear comarginal striae. Shell thickness generally moderate but high beneath plicae. 4. DISCUSSION
'Pecten' acuticosta LAMARCK only differs from 'P.' equivalvis SOWERBY (lectotype [herein designated]; BM L79783; PI. 2, Fig. 1; 1) by the angularity of the plicae. There can be little doubt that this is the result of a lower degree ot abrasion (see Section 8) and it cannot therefore be the basis for a specific distinction. Most large specimens with angular plicae which are referred to 'P. ' acuticosta are derived from low energy condensed deposits and also have relatively low umbonal angles for their heights. However, this appears to be an ecophenotypic feature brought about by relatively fast
growth in such facies (see Section 8). 'Pectinites' priscus SCHLOTHEIM was erected for a single specimen from the Sinemurian exhibiting few diagnostic features. Subsequent authors have frequently applied the specific name to small specimens of Ps. (Pseudopecten) and have maintained a specific distinction from larger specimens (= 'P. ' aequivalvis auctt.) on the basis of a lower umbonal angle and reduced number of plicae, which tend also to be acute. Notwithstanding the fact that the holotype (M) of 'Pt. ' priscus (HM) is reported to be an abnormally large specimen (H: 80, Dr. J. Helms, pers. comm., 1977) for its stratigraphic horizon, three further criteria indicate that 'P. ' priscus auctt. should be included within Ps. (Ps.) equivalvis.» JOHNSON, A. L. A. 1984. The palaeobiology of the bivalve families Pectinidae and Propeamussiidae in the Jurassic of Europe. Zitteliana, 11: 1-235, pls. 1-11. [p. 62, 64]
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Pseudopecten (Pseudopecten) equivalvis (J. Sowerby, 1816); A. L. A. Johnson, 1984, The palaeobiology of the bivalve families Pectinidae and Propeamussiidae in the Jurassic of Europe, plate 2, figures 1, 2, 4-10; ? figure 3.
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