Radulopecten vagans (J. de C. Sowerby, 1826)
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. 6, p. 82, pl. 543, figs. 3-5]
1826 Pecten vagans J. de C. Sowerby, 1826
1843 Pecten anisopleurus Buvignier, 1843
1850 Lima nerina Orbigny, 1850
1850 Pecten rhetus Orbigny, 1850
1853 Pecten hemicostatus Morris & Lycett, 1853
1853 Pecten peregrinus Morris & Licett, 1853
1859 Pecten thurmanni Contejean, 1859
1863 Pecten griesbachi Lycett, 1863
1863 Pecten rushdenensis Lycett, 1863
1863 Pecten wollastonensis Lycett, 1863 ç
1869 Pecten anomalus Terquem & Jourdy, 1869
1883 Pecten intermittens Whidborne, 1883
1886 Pecten eglus Gregorio, 1886
1886 Pecten samilus Gregorio, 1886
1906 Chlamys semicostata Cossmann, 1906
1923 Radulopecten romani Lissajous, 1923
1843 Pecten anisopleurus Buvignier, 1843
1850 Lima nerina Orbigny, 1850
1850 Pecten rhetus Orbigny, 1850
1853 Pecten hemicostatus Morris & Lycett, 1853
1853 Pecten peregrinus Morris & Licett, 1853
1859 Pecten thurmanni Contejean, 1859
1863 Pecten griesbachi Lycett, 1863
1863 Pecten rushdenensis Lycett, 1863
1863 Pecten wollastonensis Lycett, 1863 ç
1869 Pecten anomalus Terquem & Jourdy, 1869
1883 Pecten intermittens Whidborne, 1883
1886 Pecten eglus Gregorio, 1886
1886 Pecten samilus Gregorio, 1886
1906 Chlamys semicostata Cossmann, 1906
1923 Radulopecten romani Lissajous, 1923
Sowerby, J. & J. de C. Sowerby, 1812-1846, plate 543.
|
«SPEC. CHAR. Rather convex, a little longer than wide; ribs 11, large, convex, decorated with large erect concave scales that are very close upon the right but distant upon the left valve; ears nearly equal, crossed by large scales.
SYN. P. sulcatus. Geol. Survey ofthe Yorkshire Coast, p. 233. t. 9. fig. 3. excl. Syn. Seldom above an inch and a quarter wide. It differs from the last by having only half the number of ribs, and in not having the regular concentric striae which appear between the ribs in that. When young the ribs are but a little raised, although the scales are then large: a few obscure rays sometimes appear between the ribs.
This is one of those few shells which occur in several strata: it is found in Clay belonging to the Oolite near Bath (fig. 5.); in the Bath or Great Oolite at Hampton, Gloucestershire, and Bradford, Wiltshire; above the Oolite at Ancliffe; in the Cornbrash at Chatley (figs. 3, & 4.), and in the Oolite Limestone at Malton.» JAMES DE CARLE SOWERBY, 1826
|
«2. AMENDED DIAGNOSIS
Distinguished from R. varians by the smaller number of initial plicae, from R. strictus by the smaller number of radial striae, from R. inequicostatus by the relatively uniform size of the initial plicae and from all other species of Radulopecten by the existence of a non plicate phase early in ontogeny.
3. AMENDED DESCRIPTION
Disc sub-ovate, higher than long, increasing in size isometrically (text fig. 168) to a known maximum height of 50 mm (OUM J482 I , BM L9 1 533) but possibly reaching heights as great as 80 mm (see Section 7). Umbonal angle variable (text fig. 170), increasing only slightly during ontogeny. Disc flanks moderately high.
Equilateral, usuallv inequivalve with left valve more convex than right but all variations between latter and forms with right valve more convex than left. Convexity low - moderate in both valves. Intersinal distance greater in left valve than right, increasing with approximate isometry in both (text figs. 171, 172). Byssal notchdepth variable, usually moderate (text fig. 173), increasing with approximate isometry. Auricles well demarcated from disc; size variable (e. g. PI. 9, Figs. 19, 33) usually moderate, anterior slightly larger than posterior. Posterior auricles usually meeting hinge line at 90°; anterior auricles meeting hinge line at 90° or less. Anterior auricle of right valve meeting disc at an obtuse angle; remaining auricles meeting disc at an acute angle. All auricles ornamented with comarginal lamellae. Height of anterior auricle (text fig. 169) and lengths of anterior (text fig. 174) and posterior (text fig. 175) hinges variable but increasing with approximate isometry. Ornament of right valve variable (e. g. PI. 9, Figs. 23-25, 30). Between 4 and 1 4 low plicae, wider than sulci and increasing in number by Splitting. Usually less than 4% but sometimes the major proportion of specimens from a given locality also bearing up to 50 (usually about 30) radial striae (see Section 4). All specimens bearing closely spaced comarginal striae, sometimes interrupted to form a decussate pattern. In late ontogeny of specimens with relatively high plicae, comarginal striae absent from sulci and raised into lamellae on plicae. Ornament of left valve extremely variable (e. g. PI. 9, Figs. 9-22, 26-29, 31-33), essentially consisting of 2 zones. Earlier ontogenetic stages exhibiting between 15 and 35 (MNO 2901 B), most commonly about 25, radial Striae crossed by comarginal Striae which are sometimes interrupted to form a decussate pattern. Later ontogenetic stages characterised by the development of between 4 and 1 4 (MNP), most commonly 5, radial striae into low plicae which are narrower than the sulci and bear variably spaced comarginal lamellae. Remainmg radial striae rarely persisting and comarginal striae becoming decussate or absent in the sulci. Further plicae added by intercalation to a maximum number of 16 (BM 65889), most commonly 9. Height of non-plicate zone extremely variable; from afewto37 mm (BM L76308). Number of plicae at agiven height extremely variable; 0-11 (GPIG)atH: 10,0-14 (MNP) at H: 15, 0-14 (MNP) at H: 20, 5 (BM 66243) - 14 (MNP) at H: 25, 6 (MNP) - 15 (BM 65889) at H: 30, 7 (MNO) - 16 (BM 65889) at H: 35. Geographically and stratigraphically separated samples tending, however, to have a characteristic mean and coefficient of variation for the number of plicae at each height (see JOHNSON, 1981). Shell thickness moderate. The author has presented elsewhere (JOHNSON, 1981) his reasons for considenng the large range of aariation described above to be the product of developmental flexibility within a single species. 4. DISCUSSION
As the earliest taxonomic species with type specimens within the range of the species described in Section 3 'Pecten' vagans J. DE C. SOWERBY is the senior synonym for the latter. The lectotype(BM 43319; PI. 9, Fig. 31; 1) is a form in which plicae were introduced very early in ontogeny ('early developer') and has 11 plicae at H: 41. J. DE C. SOWERBY indicates by synonymising 'P.' sulcatus YOUNG and BIRD with 'P.' vagans that he included forms which the present author places in Radulopecten fibrosus within his hypodigm for 'P.' vagans. Such forms are probably the basis for his record of 'P.' vagans from the Oxfordian (Malton Oolite), a horizon at which R. fibrosus is abundant but R. vagans (i. e. the species described in Section 3) is either extremely rare or absent (see Section 5). A similar inclusion of forms which are referable to R. fibrosus may account for ROEMER's (1839) and DECHASEAUX's (1936) records of J. DE C. SOWERBY's species from the Oxfordian.
Specimens referred to 'P.' vagans by DAMON (1860, 1880) and BORISSIAK and IVANOFF (1917) are definitely referable to R. fibrosus. GOLDFUSS (1833) has applied J. DE C. SOWERBY's specific name to specimens said by SCHLOSSER (1911) to be broken examples of Ctenostreon. One of the syntypes of 'Lima' Nerina D'ORBIGNY (MNO 2879) is indeed a nember of the Limidae but the other two (MNO 2879A; PI. 9, Figs. 15, 22; 2) are 'intermediate developers' of R. vagans with 10 plicae at H: 36 and 6 plicae at H: 23 respectively. The single measurable syntype of 'P.' Rhetus (MNO 2902; 3) is similarly an 'intermediate developer' and has 6 plicae at H: 21.5. Boule (1912) erroneously described and figured the two syntypes of 'L.' Nerina which belong in R. vagans under 'P.' Rhetus. COSSMANN (1906) thought that forms like 'P.' Rhetus. (sensu D'ORBIGNY) were specifically distinct but that D'ORBIGNY's description did not constitute an adequate indication. He therefore erected the more fully characterised 'Chlamys' semicostata as a replacement specific name. The original figure of 'P.' anisopleurus BUVIGNIER (4) depicts a 'late developer' with 5 plicae at H: 28. The lectotype of 'P.' peregrinus MORRIS and LYCETT (IGS 9170; 5) is a large 'early developer' (with 9 plicae at H: 10, 11 at H: 15 and 13 at H: 20-35) while the lectotype of 'P.' hemicostatus MORRIS and LYCETT (IGS 9168; PI. 9, Fig. 18; 6) is a small 'intermediate developer'. The sole observed type of 'P. ' Wollastonensis LYCETT (BM L7631 I ; PI. 9, Fig. 9; 7) and the syntypes of 'P. ' Rushdenensis LYCETT (BM L76309, L76310; PI. 9, Fig. 16; S) are all clearly 'late-developing' forms of R. vagans, 'P.' Wollastonensis exhibiting the typical continuous comarginal striae and 'P.' Rushdenensis the more unusual decussate pattern. The sole observed type of 'P.' Griesbachi LYCETT (BM L76308; 9) is only distinguishable from the 'late developer' phenotype of R. vagans by a lack of striae and this can almost certainly be accounted for by abrasion. The holotype (M) of 'P.' intermittens WHIDBORNE (SM J4759; 10) is a small 'late developer' with 19 radial striae. The left valve figured under 'P.' anomalus TERQUEM and JOURDY has 14 plicae and is indistinguishable from R. vagans. However, the right valves have about 30 radial striae and are thus quite unlike typical right valves of R. vagans. Similar forms (e. g. PI. 9, Fig. 25) occur widely in the M. Jurassic and since there appear to be no intermediate right valve morphologies it may be that they should be accorded a specific distinction from R. vagans under TERQUEM and JOURDY's name. However, the present author is aware of no locality at which 'striate' morphs occur in the absence of 'non-striate' morphs. It therefore seems more likely that they are polymorphs of the same species rather than representatives of different species. MAUBERGI (1971) has gone so far as to suggest that they may be sexual dimorphs but the stratigraphic change in relative abundance of the morphs (see Sections 7, 10) seems to argue against this particular hypothesis. Inclusion of the 'striate' morph within R. vagans means that R. Romani LISSAJOUS and 'Ch.' rosimon COSSMANN (non D'ORBIGNY), both of which were based on such specimens, must be synonymised with R. vagans. The original figure of 'P.' Thurmanni CONTEJEAN (11) appears to depict an early developing form of R. vagans with 9 or 10 plicae at H: 10. However, the stratigraphic horizon (Kimmeridgian) is anomalously late for the latter species (see Section 5) and suggests that the figure may be a poor representation of an example of R. varians. DECHASEAUX (1936) considers CONTEJEAN's species to be closer to R. fibrosus. DE GREGORIO's figure of 'P.' samilus shows no more than a poorly preserved internal mould while that of 'P. ' eglus is only 5 mm high. However, both species exhibit 9 plicae and have a general form which suggests that they may be synonymous with R. vagans. The figured specimen of 'P.' fibrosus J. SOWERBY; QUESTENDT has 9 plicae, unlike J. SOWERBY's species. Since it is described as an example of a variable species from the Bathonian there can be little doubt of its identity with R. vagans. E. PHILLIPI's (1900) 'Aequipecten' fibrosus is similarly referable to J. de C. Sowerby's species. ARKELL (1931a) examined the original (SM) to LYCETT's Illustration (1863, pl. 33, fig. 1a) of 'P.' inaequicostatus PHILLIPS and pronounced it to be a representative of 'Ch.' (R.) anisopleurus (BUVIGNIER), a species considered above to be a junior synonym of R. vagans.» 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. 190, 193]
|
Radulopecten vagans (J. de C. Sowerby 1826); A. L. A. Johnson, 1984, The palaeobiology of the bivalve families Pectinidae and Propeamussiidae in the Jurassic of Europe, plate 9, figures 9-33, ? figure 34.
|