Leptochiton eckelsheimensis ( Gürs, 1992 )

Leptochiton eckelsheimensis ( Gürs, 1992)

Fig. 33 View FIGURE 33

Lepidopleurus eckelsheimensis Gürs, 1992, p. 6 , pl. 1, fig. 1a–e; Gürs 1995, p. 21, pl. 2, figs 5–9; Schwabe 2005, p. 94; Dell’Angelo et al. 2011, p. 953, Appendix 2; Dell’Angelo et al. 2018b, p. 18.

Lepidopleurus paeninsulae Gürs 1992, p. 7 , pl. 1, fig. 2a–c; Gürs 1995, p. 22; Schwabe 2005, p. 99; Dell’Angelo et al. 2011, p. 953, Appendix 2; Dell’Angelo et al. 2018b, p. 18.

Type material. Holotype, tail valve, figured by Gürs (1992: pl. 1, fig. 1d), Fig. 33B View FIGURE 33 . Paratypes: SMF, more than 250 valves, figured by Gürs (1992: pl. 1, fig. 1a–1c, 1e), Figs 33A, 33C, 33E–H View FIGURE 33 . Holotype of Lepidopleurus paeninsulae , tail valve, figured by Gürs (1992: pl. 1, fig. 2b), Fig. 33D View FIGURE 33 .

Type locality. Steigerberg , near Eckelsheim ( Germany) .

Type stage. Oligocene (Rupelian).

Material examined. No actual material available, only descriptions and illustrations from the literature.

Description. Head valve semicircular, flat, posterior margin widely V-shaped. Intermediate valve broadly rectangular, narrow, moderately elevated (H/W = 0.35), semicarinate in anterior profile, posterior margin straight, apices not developed, lateral areas raised. Tail valve semicircular, mucro in anterior position, antemucronal area very narrow.

Tegmentum rough. HV, LA and PMA sculptured with radial granular striae intersected by concentric growth lines, with some elevated pustules irregularly distributed on striae, concentric growth lines continuing across central area, where they weaken, becoming inconspicuous. CA and AMA sculptured with short longitudinal striae of roundish granules, weakening anteriorly, subobsolete in jugal area, which appears smooth.

Articulamentum without insertion laminae, apophyses well developed, bluntly triangular with a rounded margin.

Remarks. The description given by Gürs (1992) is incomplete, as important diagnostic information is missing. Moreover, the two intermediate and the two tail valves figured seem to differ in shape (compare Gürs 1992, figs 1b–c and 1d–e). The intermediate valve in fig. 1b could be interpreted as a valve ii (often a bit different from other intermediate valves iii–vii) and both of the valves have the longitudinal granular striae on pleural areas short, whereas Gürs (1992) noted in his description that in some other intermediate valves the sculpture may reach the anterior valve margin.

Gürs (1992) described a second species ( Lepidopleurus peninsulae ) from the Oligocene (Chattian) of Höllkopf ( Germany), that differs by the coarser pustular sculpture on the lateral areas, the smaller size of the valves and fewer radial granular striae on the postmucronal area. We do not consider these differences sufficient to warrant the specific validity of this species, and we consider L. paeninsulae a synonym of L. eckelsheimensis : this is agreement with Gürs (1995) who report Lepidopleurus peninsulae only in the discussion of Lepidopleurus jansseni .

Comparisons. The characteristics of the sculpture of Leptochiton eckelsheimensis ( Gürs, 1992) agree with the Leptochiton cancellatus group (see Tab. 2). Leptochiton eckelsheimensis is rather similar to L. lateropustulosus Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018 from the Miocene (Tortonian) of Saint-Clément-de-la-Place ( France) (see below), from which it differs mainly for the conspicuous difference in stratigraphic age, and the unavailability of the type material of L. eckelsheimensis for more accurate comparisons.

Distribution. Lower Oligocene (Rupelian): North Europe: Germany: Steigerberg ( Gürs 1995). Upper Oligocene (Chattian): North Europe: Germany: Höllkopf ( Gürs 1992, 1995).