Lepidochitona reussi ( Rolle, 1862 )

Lepidochitona reussi ( Rolle, 1862) View in CoL

Fig. 119 View FIGURE119

Chiton reussi Rolle, 1862, p. 214 , pl. 1, figs 15–16; de Rochebrune 1882, p. 57 [in synonymy of Lepidopleurus oligocaenicus

( Rolle, 1862)]; Janssen 1978, p. 226; Van Belle 1981, p. 60 [= Lepidochitona oligocaena ( Rolle, 1862) View in CoL ]; Dell’Angelo et al. 2018a, p. 11. Middendorfia (sic) reussi ; Rado 1969, p. 192, pl. 2, fig. 31. Lepidochitona reussi View in CoL ; Dell’Angelo et al. 2019b, p. 306, figs 3B, 5A–O; Dell’Angelo et al. 2020b, p. 16, fig. 11. Chiton sp. 1 ; Varone 2008, p. 156, figs 13–14. non Chiton reussi ; Vetters 1910, p. 157 [= Acanthochitona faluniensis (de Rochebrune, 1882) , fide Kroh 2003, p. 134)]. non Chiton reussi Procházka, 1895 ; Procházka, 1900, p. 72, 118, fig. 29 [= Lepidopleurus cajetanus ( Poli, 1791) View in CoL , fide Šulc,

1934, p. 4]. non Chiton reussi Rzehak, 1893 ; Rzehak, 1893, p. 171 (an undeterminable species, considered by Rzehak = Chiton siculus?

Reuss).

Type material. Syntypes: NHMW 2011/0009/0002, 1 tail valve; NHMW 2011/0009/0003, 4 valves (3 intermediate and 1 tail), Figs 119A–E View FIGURE119 ; NHMW 2011/0009/0004, 1 intermediate valve; NHMW 2011/0009/0008: 5 intermediate valves ( Dell’Angelo et al., 2019b, figs 5A–F).

Type locality. Gaas ( France) .

Type stage. Oligocene (Rupelian).

Material examined. Oligocene (Rupelian): Gaas: Syntypes NHMW plus Rupelian levels: 9 valves ( BD 942 , Fig. 119I View FIGURE119 ); Espibos: 3 valves ( AC, DA, PR); Lagouarde : 3 valves ( DA); Larrat : 209 valves ( AC, DA, JCV, Figs 119J–L View FIGURE119 , MHNBx 2020.1.1, MHNBx 2020.3.4, Figs 119F–H View FIGURE119 , MHNBx 2020.3.5, MHNBx 2020.1.7). Maximum width of the valves: 4.1 / 5.3 / 2.7 mm .

Description. Head valve semicircular, weak elevated, some radial fold may be present, slope straight. Intermediate valve broadly rectangular (W/L = 2.45–2.83), carinate in anterior profile, moderately elevated (H/ W = 0.28–0.33), anterior margin straight or slightly concave, lateral margins rounded, posterior margin slightly concave on both sides of prominent apex, lateral areas separated from central areas by a diagonal fold. Tail valve semicircular (W/L = 1.60–2.06), anterior margin slightly concave, mucro subcentral, acute, antemucronal slope straight, postmucronal slope concave.

Tegmentum entirely covered by irregularly arranged and very close-set roundish granules, not elevated, some coalescent, diameter up to 78 μm in HV, 83 μm in intermediate valves, 96 μm in tail ones; each granule bearing a central megalaesthete, and 6–10 micraesthetes arranged irregularly along margin, additional micraesthetes randomly placed between granules.

Articulamentum with small triangular apophyses in intermediate valves, trapezoidal in tail valve, slit formula 8–9 / 2 / 8–9, slits deep, teeth strong, very uneven in width, eaves spongy.

Remarks. De Rochebrune (1882: p. 57) considered “ Chiton reussi ” a synonym of “ Chiton oligocaenus Rolle, 1862 ”; however, the study of the type material of Lepidochitona reussi ( Rolle, 1862) at NHMW clarified that the two species are, in fact, distinct ( Dell’Angelo et al. 2019b.)

The studied material is generally well preserved, many valves (but not all) show a truncation in the posterior margin ( Figs 119J–L View FIGURE119 ). The valves figured by Varone (2008: figs 13–14) as Chiton sp. 1 show this characteristic truncation.

Comparisons. Lepidochitona reussi ( Rolle, 1862) differs from L. oligocaena ( Rolle, 1862) by the shape of intermediate valves (carinate with H/W = 0.28–0.33 vs. rounded with H/W = 0.27–0.54 in L. oligocaena ), the larger granules (roundish with diameter up to 96 μm vs. subrhomboidal with L up to 68 μm in L. oligocaena ), the structure of the aesthetes (with one central megalaesthete and 6–10 micraesthetes vs. aesthetes of equal size in L. oligocaena ), and the number of slits in the tail valves (8–9 vs. 9–13 in L. oligocaena ).

Distribution. Lower Oligocene: northeastern Atlantic (Rupelian): Aquitaine Basin, France: Gaas ( Rolle 1862; Dell’Angelo et al. 2019 b, 2020b).