Lepidopleurus aturriensis

Lepidopleurus aturriensis ( Dell’Angelo, Lesport, Cluzaud & Sosso, 2018) n. comb.

Fig. 1 View FIGURE 1

Leptochiton aturriensis View in CoL Dell’Angelo, Lesport, Cluzaud & Sosso, 2018a, p. 18, figs 3O–U, 4A–C; Dell’Angelo et al. 2020b, p. 49, tab. 6–7.

Type material. Holotype: MHNBx 2017.7.1, intermediate valve, width 12 mm ( Figs 1A–B View FIGURE 1 ). Paratype: MHNBx 2017.7.2, tail valve, width 9.4 mm ( Figs 1E–F View FIGURE 1 ).

Type locality. Mineur ( France) .

Type stage. Oligocene, Chattian.

Material examined. Upper Oligocene (Chattian): France: Abesse : 8 valves ( AC, DA, Figs 1 View FIGURE 1 C-D, 1G-H), Mineur: type material plus 12 valves ( AC). Maximum width of the valves: -- / 14 / 9.4 mm .

Description. Valves solid. Head valve unknown. Intermediate valves broadly rectangular (W/L = 2.42), wide, rounded in anterior profile, moderately elevated (H/W = 0.31–0.47), anterior and posterior margins straight, side margins rounded, apex inconspicuous, lateral areas raised. Tail valve semicircular, elevated, width ca. two times the length (W/L = 2.04), anterior margin straight, mucro flat, in anterior position, antemucronal slope slightly convex, postmucronal slope slightly concave just behind mucro.

Tegmentum rough, space between striae of granules large, no evidence of growth lines. LA and PMA sculptured with radial chains of large and irregular roundish granules (LA 4–6, PMA 40), tending to split near side margins. CA and AMA sculptured with longitudinal chains of large and irregular roundish granules (CA ca. 33), tending to branching and anastomosing in posterior margin near apex.

Articulamentum without insertion laminae, apophyses triangular in tail valve.

Remarks. This species was attributed to the genus Leptochiton Gray, 1847 in the original description, but the robustness and dimensions of the valves are more compatible with Lepidopleurus Risso, 1826 .

The fossil record of Lepidopleurus aturriensis ( Dell’Angelo, Lesport, Cluzaud & Sosso, 2018) is limited to the Oligocene (Chattian) of France ( Dell’Angelo et al. 2018a). The shape and sculpture of the valves are well characterized and display little variability. A single intermediate valve from Mineur is flatter, less rounded, almost subcarinated, H/W = 0.31 ( Dell’Angelo et al. 2018a: fig. 3S–T).

Comparisons. Lepidopleurus aturriensis presents a coarse sculpture, at first glance quite similar to some Lepidopleurus spp. from the Oligocene of Germany, e.g., L. benoisti (de Rochebrune, 1882) and L. vigifer (Sandberger, 1859) . Lepidopleurus aturriensis differs from L. benoisti by the higher intermediate valves (H/W = 0.31–0.47 vs. 0.33–0.36), and the more regular and less coarse sculpture, with no evidence of terraced ribs in LA and PMA; Lepidopleurus virgifer differ from L. aturriensis by the very irregular and coarse sculpture, particularly in the lateral areas of intermediate valves and postmucronal area of tail valve, sculptured with numerous diverging, coarsely granulated radial ribs, crossed by coarse growth ridges.

Distribution. Upper Oligocene: northeastern Atlantic (Chattian): Aquitaine Basin, France: Abesse, Mineur ( Dell’Angelo et al. 2018a, 2020b).