Leptochiton poirieri (de Rochebrune, 1882 )

Leptochiton poirieri (de Rochebrune, 1882) View in CoL

Fig. 35 View FIGURE 35

Lepidopleurus poirieri de Rochebrune, 1882, p. 56 View in CoL , pl. 1, fig. 10; Janssen 1978, p. 221, pl. 15, figs 20–27; Hocht 1986, p. 209; Gürs 1995, p. 23, pl. 1, figs 5–7.

Chiton Poirieri ; Cossmann 1892, p. 332, pl. 9, figs 1–2.

Chiton spec. Görges, 1941, p. 151, pl. 7, fig. 7 ( fide Janssen 1978).

Lepidopleurus ( Leptochiton) poirieri View in CoL ; Dell’Angelo & Palazzi 1989, p. 68, pls 18–19.

Lepidopleurus cf. poirieri View in CoL ; Welle 2009, p. 84, pl. 1, fig. 1.

Lepidopleurus aff. poirieri ; Müller 2011, p. 21, pl. 4, figs 1–6.

Leptochiton poirieri View in CoL ; Van Belle 1981, p. 57; Dell’Angelo et al. 2011, p. 953, Appendix 2; Dell’Angelo et al. 2018a, p. 16, figs 3G–L.

Leptochiton cf. algesirensis View in CoL [non Leptochiton algesirensis ( Capellini, 1859) View in CoL ]; Cherns & Schwabe 2019, p. 1, fig. 1 ( fide Dell’Angelo et al. 2018a).

Type material. Lectotype, designated by Janssen 1978, tail valve figured by de Rochebrune (1882: pl. 1, fig. 10b).

Type locality. Jeurre , near Étampes ( France) .

Type stage. Oligocene (Rupelian).

Material examined. Lower Oligocene: France: Gaas (Espibos, Lagouarde): 11 valves ( AC, DA, Figs 35H–I View FIGURE 35 , PR). Upper Oligocene: Germany: Glimmerode: 8 valves ( BD 256, Figs 35A–G, 35J–L View FIGURE 35 ). Maximum width of the valves: 3.6 / 2.7 / 3.8 mm.

Description: Head valve semicircular, slope straight. Intermediate valves rectangular (W/L = 2.50–2.53), rounded in anterior profile, moderately elevated (H/W = 0.32–0.43), anterior margin straight, lateral margins slightly rounded, posterior margin straight, apex not indicated, lateral areas little raised. Tail valve semicircular (W/ L = 1.86–2.00), anterior margin straight, mucro in central position, antemucronal slope straight or slightly convex, postmucronal slope almost slightly concave.

Tegmentum smooth, growth lines often present in variable numbers. HV, LA and PMA sculptured with radial series of dense, minute, roundish granules (HV 90–100, LA 20–22, PMA 75–80) joined together. CA and AMA sculptured with longitudinal series of more elliptical granules, partially overlapping (CA 80–85), with smooth and large intercostal spaces. Each granule usually with 1 megalaesthete in central position and up to 6 micraesthetes along margin.

Articulamentum lacking insertion laminae to the girdle. Apophyses are small, widely spaced, triangular but tending to become rounded in tail valve.

Remarks. This species was described on material from localities of French Oligocene, Jeurre and Étréchy (de Rochebrune 1882; Cossmann 1892) and was confirmed by Janssen (1978) for the French middle Oligocene (Auvers-Saint-Georges) and for the German middle to late Oligocene.

Comparisons. The characteristics of the sculpture of Leptochiton poirieri (de Rochebrune 1882) agree with the belonging of the species to the Leptochiton cancellatus group, see Tab. 2. Many Leptochiton species have a similar tegmental sculpture, two of them [ L. maguntiacus (de Rochebrune, 1882) and L. chatticus ( Janssen, 1978) ] are known from the Oligocene of Germany, the others still extant in Mediterranean Sea or Atlantic Ocean, and/or with a stratigraphic distribution that does not extend deeper than the Miocene.

Distribution. Lower Oligocene: North Europe, Germany: Eckelsheim, Gienberg, Trift, Welschberg, Zeilstück, ( Janssen 1978; Hocht 1986; Gürs 1995; Welle 2009; Müller 2011); Northeastern Atlantic (Rupelian): France: Paris Basin: Auvers-Saint-Georges ( Janssen 1978), Etrechy (de Rochebrune 1882); Aquitaine Basin: Gaas, Jeurre ( Dell’Angelo et al. 2018a; Cherns & Schwabe 2019); Upper Oligocene: North Europe, Germany: Glimmerode, Freden, Söllingen, Doberg, Rummeln ( Janssen 1978).