Gryphaea mima, Koppka, Jens, 2015

Koppka, Jens, 2015, Revision of the Bivalvia from the Upper Jurassic Reuchenette Formation, Northwest Switzerland — Ostreoidea, Zootaxa 3927 (1), pp. 1-117 : 22-29

Nanogyra (Nanogyra) nana (J. Sowerby, 1822)

Fig. 9.3; Fig. 10 ; Pl. 5.1–8; Pl. 6.1–4; Pl. 16.2a,b, 4, 6b * 1822 Gryphaea nana . sp. nov.—J. Sowerby: p. 114, pl. 383, fig. 3. 1829 Gryphaea mima sp. nov. —Phillips: pl. 4, fig. 6.

v 1832 Exogyra Bruntrutana , nob.—Thurmann: p.13 (nomen nudum). 1833b Exogyra auriformis nobis—Goldfuss: p. 33, pl. 86, figs. 5a,b. 1833b Exogyra spiralis nobis—Goldfuss: p. 33, pl. 86, figs. 4a,b.

1835 Exogyra spiralis Goldf. —Roemer: p. 65.

n 1839 Exogyra spiralis . β —Roemer: p. 59, pl. 18, fig. 18 [= N. (P.) welschi ( Jourdy, 1924) ]. 1845 Exogyra reniformis . (Goldfuss.)—d’Orbigny: p. 479, pl. 42, fig. 9, 10. 1846 Exogyra bruntrutana Thurmann—Leymerie : pl. 9, fig. 7.

1850 Ostrea spiralis d'Orb. 1847 —d’Orbigny: vol. 2, p. 23, no. 380. 1851b Exogyra spiralis Goldf. —Quenstedt: p. 503, pl. 40, fig. 35.

1853 Exogyra auriformis Goldfuss—Morris & Lycett : p. 5, pl. 1, fig. 7. 1857b Exogyra spiralis Goldfuss—Quenstedt : p. 752, pl. 91, figs. 31, 32.

v 1859 Ostrea (Exogyra) Bruntrutana Th. sp.—Contejean: p. 322.

1859 Exogyra spiralis Gldf. —Trautschold: p. 115, pl. 2, figs. 12–13.

1861 Ostrea spiralis d'Orb. —Thurmann & Etallon: p. 53.

v 1862 Ostrea auriformis Ctj. —Thurmann & Etallon: p. 273, pl. 38, fig. 9. 1862 Ostrea spiralis d'Orb. —Thurmann & Etallon: p. 274, pl. 39, fig. 3. n 1862 Ostrea nana Et. —Thurmann & Etallon: p. 275, pl. 39, fig. 7 (= Praeexogyra sp.).? 1862 Ostrea quadrata Et. —Thurmann & Etallon: p. 277, pl. 39, fig. 8.

1862 Ostrea subnana Et. —Thurmann & Etallon: p. 276, pl. 39, fig. 4.

1863 Ostrea bruntrutana (Thurmann) .—Dollfus: p. 87, pl. 27, figs. 7–9. 1864 Exogyra spiralis Goldf. —Credner: p. 229.

1866 Ostrea bruntrutana, Thurmann. —de Loriol in de Loriol & Pellat: p. 113 (Portlandian records). 1871 Exogyra bruntrutana Voltz—Struckmann : p. 217.

1872 Ostrea Bruntrutana Thurm. —de Loriol, Royer & Tombeck: p. 399, pl. 24, figs. 7–18. 1872 Ostrea dubiensis Contejean—de Loriol, Royer & Tombeck: p. 407, pl. 24, figs. 19–25. 1877 Exogyra nana Sow. —Blake & Hudleston: p. 265.

1877 Exogyra spiralis Gldf. —Blake & Hudleston: p. 263.

1878 Exogyra spiralis Gldf. —Trautschold: p. 254, 259, 262, pl. 3, figs. 4a–f. 1892 Ostrea (Exogyra) quadrata, Etallon. —de Loriol: p. 347, pl. 36, figs. 9–11.? 1892 Ostrea (Exogyra) subreniformis n. sp. —de Loriol: p. 347, pl. 36, figs. 12–14. 1893 Exogyra Bruntrutana Thurm. —Fiebelkorn: p. 397, pl. 14, fig. 4.

1893 Ostrea bruntrutana Thurmann—É. Greppin: p. 90, pl. 6, figs. 12, 14, 20. 1893 Ostrea (Exogyra) quadrata Etallon— É. Greppin: p. 91, pl. 6, figs. 9, 11, 13. 1897 Exogyra bruntrutana Thurm. —Futterer: p. 582, pl. 19, fig. 1, 1a.

1900 Ostrea (Exogyra) bruntrutana Thurmann—de Loriol: p. 135, pl. 17, fig. 5–8. 1900 Exogyra bruntrutana Thurm. —Müller: p. 532, pl. 18, fig. 11, 12.

? 1907 Ostrea (Exogyra) nana, Sow. —Thiéry & Cossmann: p. 29, pl. 3, fig. 22–23. 1916 Exogyra nana Sow. —Douvillé: p. 57, 77.

1921 Exogyra bruntrutana Thurmann—Newton : p. 394, pl. 11, fig. 6.

1923 Exogyra Bruntrutana Thurmann—Lewinski : p. 65, pl. 3, fig. 4,5.

1924 Exogyra nana (Sow.) —Jourdy: p. 58, pl. 2, fig. C, P, R, pl. 5, fig. 2–4, 7, 9–11, pl. 6, fig. 1–3, 5, pl. 7,

fig. 6, pl. 8, fig. 7, 8, pl. 9, fig. 1.

1924 Exogyra bathonica d´Orb.—Jourdy: p. 54, pl. 2, fig. B, pl. 5, figs. 5a,b, 12 e, f, pl. 7, fig. 5 a–d. 1926 Exogyra cf. spiralis Goldfuss—Tutcher in Buckman: p. 32, fig. 3.

1927 Exogyra bruntrutana Thurmann—Reed : p. 267, pl. 19, fig. 24.

1927 Exogyra eminensis n. sp. —Reed: p. 267, pl. 19, fig. 26.

1928 Exogyra nana Sow. —Arkell: pl. 21, fig. b.11.

1929 Exogyra nana, Sow. 1822 —Weir: p. 20, pl. 1, fig. 11–13.

1929 Exogyra bruntrutana Thurm. —Cox: p. 151.

1930 Exogyra nana (Sow.) —Weir: p. 85, pl. 10, figs. 27–29.

1930 Exogyra bruntrutana (Th.) de Loriol—Basse: p. 120, pl. 4, fig. 11a–c. 1931 Exogyra Vinassai n. sp.—Diaz–Romero: p. 35, pl. 2, figs. 17–20, pl. 3, figs. 1–2. 1931 Exogyra bruntrutana Thurmann. —Dreyfuss: p. 297, 306.

1932 Exogyra nana (Sow.) —Arkell: p. 175, pl. 17, figs. 2–21, pl. 18, figs. 3–11, pl. 19, figs. 4, 4a, Fig. 48. n 1932 Exogyra nana Sowerby sp.—Corroy: p. 194, pl. 27, figs. 12–13.

1933 Exogyra nana (Sow.) —Oria: p. 40, pl. 4, fig. 10, Text– Fig. 8–9 .

1935 Exogyra nana (Sow.) —Cox: p. 175, pl. 17, fig. 16a,b.

1939 Exogira Vinassai Diaz–Rom.—Stefanini: p. 205, pl. 22, fig. 18, pl. 23, figs. 1–11, text–figs. 16–18.

1946 Exogyra bathonica d´Orbigny—Gardet & Gerard: p. 43, pl. 7, fig. 24–25. 1947 Exogyra nana (Sowerby) —Arkell: p. 80, text–fig. 11, fig. 1.

1948 Exogyra nana (J. Sowerby) —Cox & Arkell: p. 20.

1952 Exogyra nana (J. Sowerby) —Cox: p. 92, pl. 10, figs. 2–4.

1955 Exogyra nana (Sow.) —Basse et al.: p. 664, pl. 27, fig. 3a–c.

1955 Exogyra nana (Sow.) —Gerasimov: p. 131, pl. 30, fig. 1–14.

1955 Exogyra Bruntrutana Thurmann—Schirardin : p. 46, pl. 2, fig. 13.

1958 Nanogyra nana (Sow.) —Beurlen: p. 205, 206, 207, 209, fig. 2.

1959 Nanogyra nana (Sow.) —Van de Poel: p. 222.

1959 Exogyra nana (Sow.) —Jaboli: p. 38, pl. 5, fig. 5.

1960 Exogyra nana (Sow.) —Rossi Ronchetti in Desio et al.: p. 95, pl. 11, fig. 6–8. 1964 Exogyra nana (Sowerby) 1822 —Wellnhofer: p. 52, pl. 3, figs. 8–11, fig. 33. 1965 Exogyra nana (J. Sowerby) —Cox: p. 73, pl. 11, figs. 5, 6a,b.

1965 Nanogyra nana (Sowerby) —Freneix: p. 41 (89), pl. 5, fig. 2–6.

1969 Nanogyra nana (J. Sowerby) —Fischer, J.–C.: p. 96, pl. 10, fig. 17–20. 1969 Exogyra nana —Ziegler: pl. 6, figs. 1, 2, 4, 9–10.

1971 Exogyra cf. nana (J. Sowerby) — Jordan: p. 155, pl. 18, fig. 3.

1971 Nanogyra nana (J. Sowerby) —Pugaczewska: p. 281, pl. 1, figs. 3–5, 7, pl. 2, figs. 1–4, pl. 24, figs.

1–6, pl. 25, figs. 1–7, pl. 26, figs. 1–6, pl. 27, figs. 1–6.

1971 Exogyra cf. nana (Sowerby, 1822) —Wisniewska–Zelichowska: p. 48, pl. 29, figs. 8–10. 1976 Nanogyra nana (Sowerby, 1822) —Romanov: p. 110, pl. 5, figs. 1–15. 1977 Nanogyra nana —Fürsich: p. 342, 344, 345, 348, 349, 354, 356, figs. 5, 9, 10, 12–18, 20, 22–24,

26–28.

1978 Nanogyra nana (J. Sowerby, 1822) —Duff: p. 84, pl. 9, figs. 2–5.

1981 Nanogyra nana (Sowerby 1822) —Parnes: p. 33, pl. 4, figs. 26–27.

1984 Nanogyra nana (J. Sowerby) —Gu Zhi-wei, Chen Jin-hua & Sha Jin-geng: p. 137, pl. 28, figs. 7–22. 1984 Nanogyra nana (J. Sowerby, 1822) —Kelly: p. 49, pl. 7, fig. 1–7, 9–3, Text–fig. 33. 1986 Exogyra nana (Sowerby) —Li Xiao-chi: p. 482, pl. 3, fig. 11.

n 1990 Nanogyra nana (J. Sowerby 1822) —Clausen & Wignall: p. 123, pl. 6, fig. 3 (= N. virgula , RV). 1990 Exogyra nana (Sowerby) —Turbina & Zakharov: p. 74, pl. 39, figs. 7–11. 1994 Nanogyra nana (J. Sowerby) —Duff in Martill & Hudson: p. 103, pl. 6, figs. 4–5. 1995 Nanogyra nana (Sowerby) —Jaitly, Fürsich & Heinze: p. 189, pl. 16, figs. 13–15, pl. 7, figs. 1–2. 1996 Nanogyra nana (Sowerby, 1822) —Gerasimov et al.: pl. 19, figs. 1–4. 1998 Nanogyra nana (J. Sowerby 1822) —Holzapfel: p. 108, pl. 6, figs. 6–7. 1998 Nanogyra nana (J. de C. Sowerby)—Radley et al.: p. 84, fig. 3h–3k. 1999 Nanogyra nana (J. Sowerby 1822) —Ahmad: p. 18, pl. 3, fig. 3.

2002 Nanogyra nana (J. Sowerby, 1822) —Sha, Smith & Fürsich: p. 440, figs. 11, 12.1–12.29.

v 2006 Nanogyra nana —Hicks: p. 36.

v 2006 Nanogyra nana (J. Sowerby 1822) —Richardt: p. 9, 18.

n 2011 Nanogyra nana (J. Sowerby) —Kiessling et al.: p. 210, text-fig. 13, figs. I–J.

Type series (not seen). Lectotype— Gryphaea nana J. Sowerby, 1822 , pl. 383, fig. 3 (left figure), BM 43340c, J. Sowerby Collection, Natural History Museum London ( NHMUK), designated by Arkell 1932, p. 180; refigured in Duff (1978, pl. 9, fig. 4a,b), Kimmeridge Clay of Shotover Hill, near Oxford, England; coordinates: 51°45'11.46''N, 1°11'41.58''W (centre of Shotover Hill, Headington).

Paralectotype (s)—The bivalved specimen figured in J. Sowerby (1822, pl. 383, fig. 3, right figure). The numeration of the lectotype as BM 43340c suggests the presence of more material (at least three specimens), but no further data are obtainable from the literature.

Material. Several 100 specimens from the Banné Marls (cymodoce Zone, Lower Kimmeridgian) of Vâ Tche Tchâ ( VTT), “Tunnel le Banné” (TLB) at Porrentruy, Alombre aux Vaches near Courgenay (ALO). Additional younger material comes from a hardground at the top of the mutabilis Zone (layer 4000, lallierianum Subzone, Upper Kimmeridgian) and the “Lower Virgula Marls” (layer 4500, eudoxus Zone ) of Sur Combe Ronde (SCR) and Bois de Sylleux (BSY) near Courtedoux. For measurements see Appendix, Table 2 .

Several large RVs on the original label identified as “ Ostrea bruntrutana var. portlandica Thurmann ” (= Ostrea auriformis, Ctj. , in Thurmann & Etallon 1862, p. 273) from the Banné hill (Collection number MJSN S1067, A.2.16.4.06).

Description. Shape, Size—LV capacious, globular or cup-shaped, outline usually auriform but varies between ovate, suborbicular and subtrigonal; umbo rounded; maximal convexity along the anteroventral margin; RV flat to weakly concave (convex-concave type), in adults usually with an anterior, spirally coiled carina, separating an oblique downwards directed and partly concave anterior margin. Examined specimens less than 0.1 to 2.4 cm high (Pl. 6.4; Appendix, Table 2 ).

Sculpture—LV attachment scar often large, dependant on available substrate; free surface with concentric growth lines, antimarginal furrows rare, close to attachment scar (perhaps related to xenomorphic growth) (Pl. 5.1c, 4c). RV with faint concentric growth lines and mostly regularly spaced commarginal, weakly squamous growth lamellae; antimarginal riblets always absent.

Ligament area—Narrow, exogyroid, prosodetic, deeply sunken; juvenile ligament area becoming overgrown by posterodorsal shell margin during spiral growth (Fig. 10.1–2; Pl. 5.1–7, Pl. 6.2–4). LV resilifer slightly concave, equal to or slightly broader than anterior bourrelet; posterior bourrelet narrow and mostly hidden under posterodorsal margin or “ligament ledge” ( Pugaczewska 1971, p. 222).

Internal shell characters—Umbonal cavity small to moderate (Pl. 5.2a–b); adductor scar posterocentral, oval, dorsolateral borders often slightly biconcave, weakly impressed in depositional surface, ventrally elevated (buttressed) (LV: Fig. 10.1, RV: Pl. 5.3c) (Pl. 5.2a–b, 3c; small and weakly inserted Quenstedt scar present in RV (observed only in two specimens: VTT001-7427, VTT001-144), situated at the posterior lower end of the hinge margin (Pl. 5.3c). Commissural shelf weak and restricted to dorsal half. Chomata absent.

Microstructure—Regular foliated without chambers ( Siewert 1972). RV with relatively thick outer prismatic layer, observable along the upturned growth crests of the anterior margin (Pl. 6.2a–b).

Prodissoconch, juvenile—Incomplete prodissoconch moulds visible on two RVs (Pl. 6.3a–b, and 4b–c); upper part and umbo with P1 lost (top of shell appearing flat, therefore); length of 2 measured moulds 325–344 µm, height 394 µm suggesting a prodissoconch size in the order of 350–400 µm.

Postlarval RV smooth, suboval, with straight truncated dorsal margin beyond prodissoconch (P) and a somewhat protruding posteroventral margin. First opisthogyrate torsion between ventral margin of the P and postlarval shell around 45°; strong torsion of 90° and first commarginal growth crests at ca. 0.7–1.2 mm height; shell prolongation shifted towards the former posterior margin (Pl. 6.3a and 4b,c); 2nd 90° turn between 1.7–2.5 mm, 3rd 90° turn between 2.5–10 mm and a final turn of 45° between 10 mm and adult height; altogether an opisthogyrate coiling of around 360° for adult specimens.

Paleoecology. In the low-energy marl facies of the middle Banné Member (Pl. 6.1a–c, Pl. 19.2a–d), N. (Nanogyra) nana settled preferentially on biogenic hard substrates, e.g. Trichites matheyi (Rollier, 1915) , and occasionally also on the interior of dead shells of exposed infaunal bivalves such as Ceratomya (Pl. 19.1a,b) and Integricardium . In higher energy environments, it settled on stems of Goniolina geometrica (F.A. Roemer) and other dasycladacean algae (beds 70 and 300 of section VTT, Banné Marls). These Nanogyra specimens are all smaller than 1 cm, perhaps indicating a correlation with the bending strength of the dasycladacean stems.

The species also occurs as patch reef builder together with the crinoid Apiocrinites roissyanus d'Orbigny as found along the Transjurane Highway close to Boncourt (locality Queue au Loup, BON-QLP, Upper Oxfordian). The reef of up to one meter height and several meters length contains millions of N. nana specimens forming up to 10 cm thick layers. The preservation of complete, articulated crinoid crowns indicates a rather low-energy environment. Some round, bolder-shaped oyster accumulations, built by some thousand specimens of Nanogyra nana , were found nearby in the soft marls.

Fürsich & Hautmann (2005, p. 15) reported similar lenticular patch reefs (0,2–0,3 m high) at several levels within the Kamar-e-Mehdi Formation (Middle Callovian–Lower Kimmeridgian) in east-central Iran. These reefs were found in a low energy shelf lagoon associated with sponges and bivalves ( Trichites, Radulopecten ).

Occurrence. In Switzerland and France the species is restricted to the Upper Jurassic ( Jourdy 1924, Ziegler 1969). Elsewhere, it occurs from Bajocian rocks in England (Arkell 1932) and Israel ( Parnes 1981) up to the Lower Cretaceous of the Spilsby Sandstone of England. This latter occurrence includes Nanogyra tombeckiana (d’Orbigny, 1847) (in d’Orbigny 1843–1847), which Kelly (1984, p. 46) synonymized with N. nana .

Comparisons. Larval shells of the present material of N. nana (Pl. 6.3a,b, and 4b,c) are comparable with Jurassic liostreine, Cretaceous flemingostreine and Tertiary to Recent crassostreine larval shells. The phylogenetic significance of this observation is currently unclear. See Malchus (1995), Palmer (1989) and Plates 6.5 and 10.2–3a for comparisons of various fossil oyster prodissoconchs.

The following exogyrine species described by Thurmann & Etallon (1862) (bivalve volume of Thurmann & Etallon, 1861 –1864) are considered synonymous with N. (N.) nana : Ostrea bruntrutana Thurmann & Etallon , Ostrea bruntrutana var. portlandica Thurmann (= “ Ostrea auriformis, Ctj. ”, in Thurmann & Etallon 1862, p. 273), “ Ostrea ” spiralis Goldfuss, 1833 (b) and O. subnana Etallon in Thurmann & Etallon 1862. Of these, only Ostrea bruntrutana var. portlandica is preserved in the collection of the MJSN (S1067). For a comparable specimen from the “Lower Virgula Marl” of Courtedoux see Pl. 5.6.

In addition, N. praevirgula ( Douvillé & Jourdy, 1874) appears to be a xenomorphic N. nana [see also comparisons under N. (P.) virgula ]. For detailed discussions of the synonymy and variability of adult N. nana see Arkell (1932), Cox (1952), Duff (1978), Gautret (1982), Jourdy (1924), Kelly (1984), Kiessling et al. (2011), Pugaczewska (1971) and Sha et al. (2002). The following taxa, listed alphabetically, are considered different from N. nana .

N. (N.) auricularis (Münster in Goldfuss, 1833)(b) (p. 20, pl. 79, fig.7a–b)—Münster and Goldfuss based their description of the new species on a single articulated shell (possibly holotype by monotypy, see ICZN 73.1.2) from the Liassic of Amberg (Franconia, Germany). According to Kuhn (1934, p. 6) the species appears to be restricted to the Lower Jurassic (Hettangian) in its type region. For comparison see also Jourdy’s (1924, p. 53, pl. 1, figs. 1.1–1.5, pl. 7, fig. 3) specimen(s) from the Toarcian of France, and a single RV of Nanogyra (N.) cf. auricularis , with the mould of the rarely preserved prodissoconch, from the Upper Hettangian of Stuttgart-Vaihingen from the collection of the SMNS (Pl. 10.2).

The original figure in Goldfuss (here reproduced in Fig. 11.1–2) has an oval shape and a weakly twisted, apparently prosogyrate rather than opisthogyrate umbo, which is here interpreted as a technical error during the preparation of the lithographic plate. The figured specimen can be distinguished from Nanogyra nana , by a less coiled umbo, the weakly upraised ventral margin and a much smoother RV with only few growth interruptions. The height of 4.8 cm is relatively large for a Nanogyra .

Nanogyra (N.) crassa (W. Smith, 1819) (p. 30, fig. 6)—This species was first described from the Bradford Clay (Bathonian) of Bradford-on-Avon in Wiltshire, England ( Cox & Arkell 1948, p. 20; Cox 1952, p. 90, pl. 10, fig. 1). “ Ostrea bathonica ” Thevenin, 1913 (p. 166, pl. 29, figs. 4–6) (ex. d’Orbigny, 1850) is a junior synonym ( Fischer 1969, p. 95, pl. 10, fig. 21, 22). The same may hold true for Exogyra carinata Roemer, 1835 (p. 66, pl. 3, fig. 15) from the Portland limestone of the hill Langenberg near Goslar ( Germany).

Differences to N. nana are a much larger adult size (occasionally more than 6 cm, the elongate, nearly linguiform outline , and a less curved umbo, with a well-developed resilifer and a large PAM.

Nanogyra (N.) monoptera (J.-A. & J.F.E. Eudes-Deslongchamps, 1858) (p. 159, pl. 5, figs. 1–4)—This is another early representative of the genus, known from the Toarcian of France. The species differs from N. nana by its sickle-shaped prolongation of the posteroventral margin, the presence of a posterodorsal auricle, and a minor inflation.

Nanogyra (N.) rivelensis (de Loriol, 1904) (p. 256, pl. 25, figs. 11–13)—The species is from the Argovian marly sponge facies (“Couche à Birmenstorf”, transversarium Zone, Middle Oxfordian) of the Mont Rivel near Champagnole (Franche-Comté, Department Jura, France), which also exists in the Swiss Jura chains (Fig. 11.7–8). Ostrea striata Münster in Goldfuss (1833)(b) (p. 22, pl. 80, figs. 3a–d) from the Oxfordian of Southern Germany is a senior synonym (see Gümbel 1862, p. 194–208, for type section). The name has rarely been used, however, and should be considered a nomen oblitum. This decision would also avoid confusion with Chama striata W. Smith , which is itself a suppressed senior synonym of Nanogyra (P.) virgula (Deshayes) (ICZN opinion 310). Original figures 3a–c in Goldfuss (1833)(b) are here reproduced as Figure 11.3–5.

Differences to N. nana are the much larger height (H 5.6 cm) and a more subrectangular shape, with a less twisted umbo (thus also a broader and less curved ligament area). The RV is dorsally nearly smooth, plain, occasionally covered by concentrically arranged small pustules, followed ventrally by growth lamellae (Fig. 11.3, 6–7). A well-developed anterior to nearly central carina separates a much broader area of towering commarginal growth laminae (Fig. 11.7). The LV is less inflated than in N. nana and covered by strong concentric growth squamae (Fig. 11.5).

Nanogyra ? (Nanogyra) roederi (de Loriol, 1904) (p. 254, pl. 25, figs. 14–21)— Roeder (1882, p. 36, pl. 1, figs. 3a–d, pl. 2, fig. 1) discovered the species in the “Terrain à Chailles” (Lower Oxfordian) near Ferrette (= Pfirt, Alsace, France) but identified it as “ Exogyra reniformis Goldfuss ”. The species is also present in the Lower and Middle Oxfordian of Switzerland.

De Loriol’s species is almost homeomorphous to N. nana . However, it differs by a slightly protruding anterodorsal auricle, the lack of commarginal growth crests on the RV where the anterior area with steep towering growth laminae/crests is narrower in N. roederi than in N. nana . The laminae themselves are also thinner and less numerous (ca. 8 for N. roederi versus 10–20 for N. nana ). Further differences are a smaller and more anteriorly located attachment area for N. roederi and a larger, more dorsally situated PAM of the RV. Presence or absence of chomata is unknown for N. roederi .

Nanogyra (N.) tramauensis ( Cox, 1952) (p. 94, pl. 10, figs. 5a–c, 6a–c)—This is a large, auriform species of Nanogyra from the Lower Oxfordian of western India (Tramau, Kutch district).

Differences to N. nana are the more subrectangular shape, a larger adult size (H 5.5 cm, L 4.3 cm, I 2.4 cm, dimensions of holotype), a less curved umbo and a convex RV without any concentric growth lamellae.

Nanogyra (Palaeogyra?) fourtaui ( Stefanini, 1925) (p. 168, pl. 39, fig. 3)—This small species was originally described from the Callovian and Oxfordian of Somalia. The species was recently synonymized with Nanogyra (N.) nana (see Kiessling et al. 2011, p. 210; text-fig. 13, figs. I–J). However, this view is difficult to hold up after comparing the European N. nana with Stefanini’s original figures and with Kiessling et al.’s figured images, which were kindly re-photographed at higher magnifications by M. Aberhan (NM Berlin) (Fig. 12.1–5).

The left valve of N. fourtaui tends to have a very small attachment scar, a remarkably pointed umbo which is much less opisthogyrate, and a much stronger posterior curvature than N. nana . Also, the posterior flank of the RV is pronouncedly concave and its surface lacks the shallow terrace-like growth steps of the European species. In addition, the surface shows some widely spaced minute antimarginal riblets on the posteroventral portion which have never been found on any European N. nana (Fig. 12.3). In fact, both characters would be more typical of the subgenus N. (Palaeogyra). However, this cannot be ascertained without demonstrating the presence of chomata in the Somalian species. Unfortunately, all published images show tightly articulated shells so that internal characters of this species remain unknown.

Nanogyra (Palaeogyra) welschi ( Jourdy, 1924) (p. 70; pl. 2, fig. V.s.; pl. 6, fig. 7; pl. 8, fig. 11o)—The species was originally described from the Lower Kimmeridgian of Tout-y-Faut (north of Saint-Jean-d’Angély, Charente- Maritime) in France. Eight syntypes are preserved in the Muséum national d’Histoire naturelle in Paris (No. MNHN.F.R52857). Exogyra gumprechti Schmidt, 1905 (p. 161, pl. 6, figs. 2–5) from the Lower and Middle Kimmeridgian of Pomerania (NW Poland) seems to be a widely overlooked senior synonym ( Deecke 1907; Krause 1908).

The species is of similar shape and size as N. nana but possesses chomata ( Pugaczewska 1971, p. 294; pl. 1, figs. 2, 6; pl. 33, figs. 1–5; pl. 34, figs. 1–3). It also differs by having a less curved and more pointed umbo, antimarginal riblets and furrows on the LV, and usually a nearly smooth RV with a weakly developed anterior carina and without upturning commarginal growth crests of the anterior area.

Figures

FIGURE 8. Circunula n. gen. cotyledon (Contejean, 1859). Group of juvenile LVs attached interior, of a bivalved Trichites (CGN-ALO 009 - 1, largest oyster specimens labelled from I-IV, see also Fig. 6), close to its ventral margin; Alombre aux Vaches (Canton Jura), Lower Kimmeridgian, Banné Marls. Scale x 1.5.

FIGURE 9. Comparison of juvenile RVs of Gryphaea, Nanogyra, and Actinostreon. 1. Gryphaea ferruginea Terquem, 1855, Aalenian, Poland (redrawn after Pugaczewska 1971 b, fig. 1). 2. Nanogyra (Palaeogyra) virgula (Deshayes, 1831), Upper Kimmeridgian, Switzerland. 3. Nanogyra (N.) nana (J. Sowerby, 1822), Lower Kimmeridgian, Switzerland. 4. Actinostreon marshii (J. Sowerby, 1814), Callovian, Lithuania.

FIGURE 10. Nanogyra (Nanogyra) nana (J. Sowerby, 1822). 1, LV, interior, VTT 001 - 3214; scale x 2. 2 – 3. Articulated valves, VTT 001 - 3210; scale x 3: 2, LV, RV lateral; 3, LV lateral, posterior xenomorphic; Vâ Tche Tchâ, Banné Marls, Lower Kimmeridgian.