Lepidochitona corrugis ( Boettger, 1869 )

Lepidochitona corrugis ( Boettger, 1869)

Fig. 128 View FIGURE 128

Chiton corrugis Boettger, 1869, p. 11 , pl. 1, figs 14a–14c; Boettger 1870, p. 40, pl. 9, figs 14a–14c; Wenz 1932, p. 14.

Gymnoplax corrugis ; de Rochebrune 1882, p. 60.

Lepidochitona corrugis ; Van Belle 1981, p. 31; Dell’Angelo et al. 2011, p. 953, Appendix 2; Dell’Angelo et al. 2015a, p. 365; Dell’Angelo et al. 2019b, p. 306; Dell’Angelo et al. 2020b, p. 306.

Middendorfia corrugis ; Marquet et al. 2008, p. 11, pl. 1, fig. 1; Lozouet & Maestrati 2012, figs 172.23–25.

Chiton terquemi Deshayes, 1861, p. 193 , pl. 13, figs 1–4 [non C. terquemii Deslongchamps, 1859 ]; Van Belle 1981, p. 76

Ischnochiton terquemi ; Fischer P.-H. 1959, p. 78.

Tonicia etrechyensis de Rochebrune, 1882, p. 54 [nom. nov. pro Chiton terquemi Deshayes, 1861 , non C. terquemii Deslongchamps, 1859 ]

Chiton etrechyensis ; Cossmann 1892, p. 332; Van Belle 1981, p. 36.

Tonicia mamillata de Rochebrune, 1882, p. 54 , pl. 3, fig. 1; Van Belle 1981, p. 49 ( fide Janssen 1978).

Chiton sp. Gillet, 1953, p. 399, pl. 1, figs 4, 4a ( fide Janssen 1978).

Type material. Lectotype SMF 14.32 About SMF a designated by Janssen 1978, the intermediate valve figured by Boettger (1969: pl. 1, figs 14a–14c) ; Paralectotype SMF 14.32 About SMF b.

Type locality. Gienberg ( Germany) .

Type stage. Oligocene (Rupelian).

Material examined. Oligocene: France: Ormoy-La-Rivière: 60 valves ( BD 951, Figs 128A–L View FIGURE 128 ); Auvers-Saint-Georges:(3 valves ( BD 952); Morigny: 2 valves ( BD 953). Maximum width of the valves: 3.4–4.3– 1.5 mm.

Description. Head valve semicircular, posterior margin widely V-shaped, some radial folds may be present. Intermediate valves broadly rectangular (W/L = 2.14–2.75), moderately to highly elevated (H/W = 0.38–0.60), semicarinate in anterior profile, anterior margin almost straight to slightly concave between apophyses, side margins rounded, posterior margin almost straight, with a small apex, lateral areas from scarcely differentiated from central areas to raised and separated by a diagonal fold. Tail valve semicircular, elevated, anterior margin almost straight, mucro subcentral or slightly anterior, AMA and PMA areas poorly differentiated, postmucronal slope slightly concave.

Tegmentum uniformly covered with rounded to diamond-shaped granules, irregularly arranged in more or less distinct vertical rows in CA and AMA, in diverging rows running obliquely in LA.

Articulamentum with apophyses wide, but only slightly projecting, with broad sinus, slit formula 8 / 2 / 8, the second small slit in intermediate close to posterior margin, eaves coarsely spongy.

Remarks. This species was described by Boettger (1869) upon two intermediate valves from the Oligocene of Gienberg ( Germany). Later, Janssen (1978) re-examined the type material and considered Tonicia etrechyensis de Rochebrune, 1882 (nom. nov. pro Chiton terquemi Deshayes, 1861 , non C. terquemii Deslongchamps, 1859 , from the lower Jurassic of France) and Tonicia mamillata de Rochebrune, 1882 , identical to Lepidochitona corrugis ( Boettger, 1869) , therefore junior synonyms of the latter species.

Janssen (1978) figured two intermediate valves from Ormoy-La-Rivière ( type locality of T. mamillata ) and two valves (intermediate and tail) from Auvers-Saint-Georges.All three species ( Lepidochitona corrugis , L. etrechyensis , L. mamillata ) have been described from intermediate valves, with the first figure of a tail valve provided by Janssen (1978: pl. 16 fig. 43).

Boettger evidenced the strong similarity of C. corrugis with C. terquemi Deshayes, 1861 . The taxa could be distinguished by the greater elevation of the valves: 0.35 ( C. corrugis ) vs. 0.48 ( C. terquemi ), extracted from Boettger and Deshayes’ figures, respectively for), and the subdued lateral areas, without a diagonal rib to separate LA from CA in C. terquemi .

The abundant material (Ormoy-La-Rivière and Auvers-Saint-Georges) available to study documents the great morpological variability of some characters, e.g.,: (1) the presence ( Figs 128A–B View FIGURE 128 ) or the absence ( Fig. 128H View FIGURE 128 ) of radial depressions on the head valve; (2) the large variability of the height-width ratio in intermediate valves ( Fig. 128D, H View FIGURE 128 /W = 0.39; Fig. 128J, H View FIGURE 128 /W = 0.43; Fig. 128G, H View FIGURE 128 /W = 0.60); (3) LA of intermediate valves scarcely differentiated from CA ( Figs 128C, 128I View FIGURE 128 ) or raised and separated by a diagonal fold ( Fig. 128E View FIGURE 128 ).

Comparisons. This species differs from the other Oligocene Lepidochitona because of the sculpture of CA and AMA (granules arranged in more or less distinct longitudinal striae), and LA and PMA (granules arranged in diverging striae running obliquely), vs. a sculpture with granules randomly arranged on the entire valve, typical of the species of Lepidochitona from Gaas (see Tabs 19, 21).

Distribution. Lower Oligocene: North Europe, Germany: Gienberg ( Boettger 1869; Janssen 1978); Northeastern Atlantic: Paris Basin: France; Auvers-Saint-Georges, Morigny, Ormoy-La-Rivière ( Janssen 1978; Lozouet & Maestrati 2012; this study); Belgium ( Marquet et al. 2008).