Radulopecten fibrosus (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. 84, pl. 136, fig. 2]
1816 Pecten fibrosus J. Sowerby, 1816
1822 Pecten sulcatus Joung & Bird, 1822
1850 Pecten subfibrosus Orbigny, 1850
1862 Pecten veziani Étallon in Thurmann & Étallon, 1862
1917 Pecten socolowi Borissiak & Ivanoff, 1917
1931 Chlamys (Aequipecten) superfibrosa Arkell, 1931
1934 Pecten (Aequipecten) fibrosus var. duplicostatus Stoll, 1934
1934 Pecten (Aequipecten) tenuicostatus Stoll, 1934 [nomen novum pro Pecten fibrosus Goldfuss]
1956 Chlamys (Radulopecten) drewtonensis Neale, 1956
1822 Pecten sulcatus Joung & Bird, 1822
1850 Pecten subfibrosus Orbigny, 1850
1862 Pecten veziani Étallon in Thurmann & Étallon, 1862
1917 Pecten socolowi Borissiak & Ivanoff, 1917
1931 Chlamys (Aequipecten) superfibrosa Arkell, 1931
1934 Pecten (Aequipecten) fibrosus var. duplicostatus Stoll, 1934
1934 Pecten (Aequipecten) tenuicostatus Stoll, 1934 [nomen novum pro Pecten fibrosus Goldfuss]
1956 Chlamys (Radulopecten) drewtonensis Neale, 1956
J. Sowerby & J. de C. Sowerby, 1812-1846, plate 136.
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«SPEC. CHAR. Depressed, orbicular, with a rectangular beak, nine or ten broadish diverging grooves and numerous sharp concentric striae; ears equal, rectangular; margin undulated internally.
Rather longer than broad; the back is formed of two straight lines meeting at an angle, sometimes greater, but seldom less than a right angle; the undulations within the margin are regular and rather deep. The striae are composed of small very prominent sharp ridges that hold the shell firmly to the stone in which it lies.
This is remarkable at first sight for its broad and few sulci, and for the fine undulating transverse striae all over them. I have but seldom seen it in pairs, but Mr. Strangewayes has a pair from Carrington, Oxfordshire, and I have an excellent specimen from the Chatley Cornbrash, by favour of T. Meade,esq. and a small one showing the inside from Oxfordshire. These last two are figured. Mr. Mantell was so kind as to send me one from North Leach, Gloucestershire, which has only 9 costae, and Mrs. Gent has met with something similar, but plainer at Kellaways; if these should prove to be distinct species, I shall notice them again.» JAMES SOWERBY, 1816
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«2. AMENDED DIAGNOSIS
Distinguished from R. scarburgensis by the lack of radial striae, from R. inequicostatus by the larger number of plicae, from R. sigmaringensis by the lamellose rather than spinose ornament and from all other species of Radulopecten by the lack of a non-plicate zone.
3. AMENDED DESCRIPTION
Disc sub-ovate, higher than long, growing allometrically (text fig. 185) to become more orbicular near the maximum height of 43.5 mm (BM L42148). Umbonal angle increasing during ontogeny but relatively invariant at any one size (text fig. 187). Disc flanks low.
Equilateral, inequivalve, low convexity, left valve more convex than right. Intersinal distance greater in left valve than right, increasing with approximate isometry in both (text figs. 188, 189). Byssal notch depth variable, small to moderate. Auricles well demarcated from disc, variable in size, anterior larger than posterior. All auricles meeting hinge line at about 90°. Anterior auricle of right valve meeting disc at about 90°, remaining auricles meeting disc at an acute angle. All auricles ornamented with closely spaced comarginal striae. Height of anterior auricle (text fig. 186) and lengths of anterior and posterior auricles (text figs. 190, 191) variable. Left valve ornamented with between 10 and 13,usually 11, original plicae (text fig. 192), narrower than sulci. Height of plicae variable, usually moderately high in early representatives (e. g. PI. 10, Fig. 8) but uniformly low in late forms (e. g. PL 10, Figs. 13, 16-18). Additional low plicae intercalated during ontogeny of forms with original plicae to give a maximum total number of 27 (BM 35563). Rate of intercalation apparently faster in some of the latest representatives (see Section 7). Forms with low plicae bearing evenly spaced comarginal lamellae on all parts of disc. Comarginal lamellae restricted to plical crests in forms with high plicae. Right valve usually bearing one less plica than left, with plicae wider than sulci and all parts of disc ornamented with closely spaced comarginal striae. Shell thickness moderate in early representatives, low in later forms (see Section 7). 4. DISCUSSION
Of the two syntypes of 'Pecten' fibrosus J. SOWERBY one (BM 43305; PI. 10, Fig. 21) is seen only from the interior and the other (BM 43306; PI. 10, Fig. 20) is poorly preserved. Metric proportions (1) and general shape of the former, designated as lectotype by ARKELL (1931 a), are, however, indistinguishable from the species described in Section 3 and since J. SOWERBY's name is the earliest available for this species it is known hereinafter as Radulopecten fibrosus. The second syntype (paralectotype) has metric proportions (2) within the range of R. fibrosus and the shape of the auricles confirms that it is a member of the latter species. The superficial similarity of the disc ornament in this specimen to that of R. scarburgensis (YOUNG and BIRD) is presumably the reason for PHILLIPS' (1829) misapplication of J. SOWERBY's specific name to an example of YOUNG and BIRD's species. Perhaps through following PHILLIPS' rather than J. SOWERBY's usage of 'P.' fibrosus, D'ORBIGNY (1850) applied this name to specimens (MNO 3397) of R. scarburgensis and saw fit to erect a new species, 'P.' subfibrosus, for specimens (MNO 3754; PI. 10, Fig. 22) which are in fact typical representatives of J. SOWERBY's species. Other authors (DAMONI, 1860, 1880; ROEDER, 1882; DOUVILLE, 1916; DECHASEAUX, 1936, pl. 6, figs. 18,18a, 19, pl. 7, fig. 1) have also applied J. SOWERBY's specific name to examples of R. scarburgensis so with the evident possibility of misinterpretation of his hypodigm inadequately characterised records of his species in LAMARCK (1836), BEAN (1839), OPPEL (1858), COQUAND (1860), LAUBE (1867), TERQUEM and JOURDY (1869), KILIAN and GUEBHARD (1905), READ et al. (1925), BARBULESCU (1971) and WORSSAM and IVIMEY-COOK (1971) can only be tentatively synonymised. Although most subsequent usages of 'P.' subfibrosus have been for forms which are undoubtedly within D'ORBIGNY's hypodigm (= R. fibrosus), de LORIOL (1901) describes under 'P.' ('Chlamys') subfibrosus speeimens which are almost certainly representative of R. scarburgensis. Doubt must therefore be cast on the affinities of unfigured specimens referred to D'ORBIGNY's species by the same author in 1897, 1900 and 1904, although those described in 1894 do appear to belong to R. fibrosus. COQUAND's (1860) record of 'P. ' subfibrosus is accompanied by neither a figure nor a description so it can only be tentatively synonymised. BRONN (1852) followed D'ORBIGNY's Interpretation of J. SOWERBY's hypodigm but considered that specimens such as those forming the basis for 'P.' subfibrosus could only be distinguished at the varietal level. Thus forms belonging to R. scarburgensis were referred to as 'P.' fibrosus α and forms belonging to R. fibrosus were referred to as 'P.' fibrosus ß. STOLL's (1934) variety duplicostatus is nothing more than the quite common form of R. fibrosus in which intercalation of additional plicae has occurred.
QUENSTEDT's (1852) and E. PHILIPPI's (1900) misapplication of J. SOWERBY's specific name to specimens of R. vagans is discussed under the latter species. Certain specimens illustrated by DECHASEAUX (1936, pl. 6, fig. 20, pl. 7, figs. 2, 3) under 'Aequipecten' fibrosus may also be referable to R. vagans although the horizon (Oxfordian) suggests that they more probably belong in R. inequicostatus. Specimens illustrated under 'P.' vagans by DAMON (1860, 1880) and BORISSIAK and IVANOFF (1917) are clearly representative of R. fibrosus. 'P.' sulcatus YOUNG and BIRD and P. ('Ae.') tenuicostatus STOLL, both with 11-12 original plicae, are typical early representatives of R. fibrosus. The figured specimen of 'P.' Vezlani ÉTALLON (3) and the syntypes of Ch. ('Ae.') superfibrosa ARKELL (OUM J8247-8252; PI. 10, Figs. 11,12; 4) are small late representatives with rather extreme depression of the plicae. Large late representatives of R. fibrosus with the characteristic numerous low plicae were incorrectly referred to 'P.' Midas D'ORBIGNY (a junior synonym of Camptonectes (C.) auritus) by DOLLFUS (1863) and this misusage of D'ORBIGNY's specific name has been perpetuated by DAMON (1880) and ARKELL (1931a). It may therefore be that inadequately characterised specimens referred to D'ORBIGNY's species in de LORIOL et al. (1872) and de LORIOL and PELLAT (1875) are in fact representatives of R. fibrosus. The holotype (OD) of 'Ch.' (R.) drewtonensis NEALE (BM 88737; PI. 10, Fig. 24) has 13 plicae and most metric proportions (5) within die range of R. fibrosus. However, the byssal notch is abnormally large and may indicate that NEALE's specimen is indeed a member of a different species. Nevertheless the paucity of comparable specimens makes it more likely that 'Ch.' (R.) drewtonensis represents extreme variation within R. fibrosus. 'Ch.' (R.) qualicosta ÉTALLON; CHAVAN has irregular plicae but seems to be nearer R. fibrosus than ÉTALLON's species (= R. varians). 'P.' ('Ae.') Triboleti ROLLIER was compared with 'P.' fibrosus but the figured specimen is too poorly preserved to allow confident assignment to any species. The affinities of 'P.' Thurmanni CONTEJEAN are discussed under R. vagans. 'P.' Sokolowi BORISSIAK and IVANOFF (erected for a form with 13 plicae which is inseparable from R. fibrosus) must be rejected as a junior primary hononym of 'P.' Sokolowi RETOWSKI (? = Propeamussium (P.) nonarium q. v.).» 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. 204-207]
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Radulopecten fibrosus (J. Sowerby 1816); A. L. A. Johnson, 1984, The palaeobiology of the bivalve families Pectinidae and Propeamussiidae in the Jurassic of Europe, plate 10, figures 7-18, 20-22, ? figure 24.
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«Remarks. The synonymy and range of variation of this species has been fully discussed by Arkell (1931, p. 112), and little need be added here. The few Oxford Clay specimens known, from Stewartby, Norman Cross and "Chippenham", are medium-sized specimens which show clearly the wide flat-topped ribs on the right valve, 11-16 in number, and the comarginal striae passing over the auricles. GSM 113408, from the "Oxford Clay of Chippenham", is unusual in that there appear to be about 16 radial ribs on the right valve, but as it is only possible to gain an internal view of the valve, style of ornament and rib pattern cannot be examined, and this specimen is assigned to C. (R.) fibrosa tentatively. However, the ctenolium and the vertical ridge and groove system along the hinge margin, are very well seen, and it is clear that there was a functional byssus in the adult. A pair of cardinal crura, radiating from the apex of the resilifer and running subparallel to the hinge margin, are also well seen (Text-fig. 24). Another unusual feature of this specimen is the size and extent of the anterior auricle, which seems rather large for C. (R.) fibrosa.
Stoll's (1934, p. 21) division of C. (R.) fibrosa into three is, as noted by Arkell (1935, p. xiii), unacceptable, as all her figured specimens fit the variation seen within Sowerby's species. Chavan's (1952, p. 36) C. (R.) fibrosa var. also belongs to the range of variation o f this species. Only one of Dechaseaux's (1936, p. 47, pl. 6, figs. 16-16a) specimens may be referred to C. (R.) fibrosa, the others belonging to C. (R.) scarburgensis and to two other species. C. (R.) drewtonensis Neale, from the calloviense Zone Kellaways Rock of South Cave, Humberside, is undoubtedly closely related, but differs in the nature of the ornament on the anterior auricle, possesses radial striae on the proximal part of the right anterior auricle, and it has wider, flatter, more prominent ribs on the right valve. Range and occurrence. Abundant at many levels between the Kellaways Rock and the Corallian Beds (Arkell 1931, p. 112), and sparingly in the medea and grossouvrei subzones at Stewartby, and in the medea and jason subzones at Norman Cross; ? "Oxford Clay of Chippenham" (GSM 113408) and Kellaways Rock of the Snowsdown borehole, Kent (GSM K1342). Middle to Upper Oxford Clay of Oxfordshire, and Hackness Rock of Scarborough. Callovian and Oxfordian of France, Germany, Switzerland and Russia.» DUFF, K. L. 1978. Bivalvia from the English Lower Oxford Clay (Middle Jurassic). Palaeontographical Society. Monograph 553: 1-137, pls. 1-13. [p. 73, 74]
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Chlamys (Radulopecten) fibrosa (J. Sowerby, 1816); K. L. Duff, 1978, Bivalvia from the English Lower Oxford Clay (Middle Jurassic), plate 6, figures 2, 7-9.
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