Lepidopleurus pseudobenoisti, Dell'Angelo, Landau, Van Dingenen & Ceulemans, 2018

Lepidopleurus pseudobenoisti View in CoL Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018

Fig. 5 View FIGURE 5

Lepidopleurus pseudobenoisti View in CoL Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018b, p. 8, fig. 3; Dell’Angelo et al. 2020b, p. 52, tab. 9.

Type material. Holotype MNHN.F.A67049, tail valve ( Figs 5A–B View FIGURE 5 ) . Paratypes: MNHN.F.A67050–A67052 (3 valves); NHMW 2017/0108/0003–0005 (3 valves); RGM.1008393–1008395 (3 valves) .

Type locality. Saint-Clément-de-la-Place ( France) .

Type stage. Miocene (Tortonian).

Material examined. Upper Miocene: France: Saint-Clément-de-la-Place: type material plus 697 valves ( MNHN.F.A67053–A67059, Figs 5E–F, 5I–J View FIGURE 5 ), NHMW 2017/0108/0006, RGM.1008349, RGM 1008396, RGM 1008414, RGM 1008427, RGM 1008440, BD 131, Figs 5C–D, G–H, K–L View FIGURE 5 ), Sceaux d’Anjou: 2 valves ( RGM 1008443 , BD 132 ). Maximum width of the valves: 15.5 / 26.2 / 18.3 mm .

Description. Valves solid. Head valve large, semicircular, posterior margin widely V-shaped, slope almost straight or slightly convex interrupted by profile of concentric, terraced ribs. Intermediate valves wide, broadly rectangular, width more than three times the length (W/L = 3.16–3.44), rounded in anterior profile, moderately elevated (H/W = 0.25–0.33), anterior margin slightly convex, side margins rounded, posterior margin straight, apex inconspicuous, lateral areas strongly raised. Tail valve semicircular, elevated, width slightly less than twice length (W/L = 1.72–1.85), anterior margin straight and slightly convex in jugal area, mucro strongly pronounced, in anterior position, antemucronal slope decidedly convex, postmucronal slope concave just under mucro, interrupted by profile of concentric, terraced ribs.

Tegmentum coarse, space between striae of granules large. HV, LA and PMA sculptured with numerous and strongly irregular branching or anastomosing radial chains of granules, intersected by some prominent concentric, terraced ribs (up to 5–6 in LA). CA and AMA sculptured with numerous longitudinal chains (ca 60 in CA) of roundish, large granules (diameter up to 100 µm), more regular in central part, markedly irregular and tending to branching and anastomosing laterally near side margins, sculpture on CA even more irregular and coarser than on AMA. Each granule with a central megalaesthete and up to 20 micraesthetes irregularly disposed along margin.

Articulamentum without insertion laminae, apophyses narrow, triangular, widely projected on intermediate valves, larger and rounded on tail valves, muscle scars particularly well preserved on tail valves.

Remarks. The valves examined are the largest found in the genus Lepidopleurus . In spite of the relative abundance of fossil material, only a few valves preserve their features complete, many missing the apophyses.

The sculpture is variable, especially with respect to the longitudinal chains of granules in CA, which tend to branch and anastomose irregularly. It is difficult to count the number of longitudinal chains of granules, ca. 60 counted on the anterior margin. The longitudinal chains in the holotype are more regular, almost parallel and with only a few chains branching and anastomosing in the jugal area ( Fig. 5A View FIGURE 5 ).

The intermediate valves have irregular sculpture ( Dell’Angelo et al. 2018b). Some valves ( Fig. 5I View FIGURE 5 ) display a sculpture in CA in which some longitudinal chains are missing, and a very irregular sculpture in LA. Numerous small valves are interpreted as juvenile specimens of L. pseudobenoisti ( Dell’Angelo et al. 2018b: fig. 2P–R), showing smaller roundish granules (diameter ca. 65–75 µm), with a central megalaesthete and fewer micraesthetes (7–10) regularly disposed along the margin.

Comparisons. Lepidopleurus pseudobenoisti Dell’Angelo, Landau, Van Dingenen & Ceulemans, 2018 is superficially similar to L. benoisti (de Rochebrune, 1882) , but L. pseudobenoisti differs most importantly by the different shape of the tail valve with the strongly pronounced mucro and also by the coarser and more variable sculpture and the considerably more elevated lateral areas of intermediate valves. Another similar species is Lepidopleurus virgifer (Sandberger, 1859) (see below), from which L. pseudobenoisti differs by its smaller size and the shape of the tail valve with a strongly pronounced mucro.

Distribution. Upper Miocene: northeastern Atlantic (Tortonian): Anjou, France: Saint-Clément-de-la-Place, Renauleau, Sceaux d’Anjou ( Dell’Angelo et al. 2018b).