Meiersia, Monari & Valentini & Conti, 2011

Monari, Stefano, Valentini, Mara & Conti, Maria Alessandra, 2011, Earliest Jurassic patellogastropod, vetigastropod, and neritimorph gastropods from Luxembourg with considerations on the Triassic-Jurassic faunal turnover, Acta Palaeontologica Polonica 56 (2), pp. 349-384 : 374-375

Genus Meiersia nov.

Type species: Meiersia disarmata sp. nov. (see below). Late Hettangian , Luxembourg; see below .

Etymology: The genus is dedicated to Kurt Meiers, passionate collector of fossils cooperating with the National Museum of Natural History of Luxembourg.

Diagnosis.—Adult shell sinistral, discoidal−lenticular and with almost flat spire. Base swollen and widely umbilicated. Aperture subcircular to subtrapezoidal, weakly angulated at the periphery. Peristome with upper part of outer lip slightly convex to almost straight. Periphery corresponding to a sharp flange bearing dense crenulations or distinct and widely spaced spines. Base smooth, evenly convex to subangulated in its median part. Growth lines strong.

Remarks.—We identified two species belonging to Meiersia gen. nov., namely the type species Meiersia disarmata sp. nov. and Meiersia calcar (Orbigny, 1853) (Orbigny 1853: 378, pl. 340: 5–7; Fischer and Weber 1997: 150, pl. 21: 3) a species known from the Pliensbachian sediments of Calvados ( France). Koken (1896, 1897) ascribed the latter species to the genus Asperilla Koken, 1896 . However, the type species of Asperilla , Asperilla coronoserra (Quenstedt, 1884) (= Delphinula longispina Rolle, 1860 ) from the Kimmeridgian of Swabia (southern Germany) is characterised by a dextral shell provided with a strong spiral cord on the central part of the base (Quenstedt 1884: 413, pl. 201: 45, 46; Brösamlen 1909: 237, pl. 19: 15). These aspects clearly differentiate Asperilla from Meiersia . Moreover, A. coronoserra is provided with a further, narrower spiral cord at the periumbilical edge.

Cossmann (1916) and Fischer and Weber (1997) treated Asperilla as subgenus of Platyacra Ammon in Zittel, 1882. Platyacra differs from Meiersia in having a characteristic dimorphic shell. In the former genus the early spire is planispiral with a concave apical side, and the adult shell is pagodiform due to the peripheral carina placed much above the suture. On the contrary, in Meiersia the early spire, though strongly depressed, shows the first observable whorls convex. Moreover, the adult shell is lenticular and with the peripheral carina in contact to the suture.

The specimen from the Pliensbachian of Calvados ( France) ascribed by Cossmann (1916: 208, pl. 9: 10–12) to Platyacra (Asperilla) calcar (Orbigny, 1853) is a sinistral shell which is distinguished from the holotype of Orbigny’s (1853) species by a more marked periumbilical angulation bearing small nodes, and in the presence of some spiral threads on the surface of the base, between the peripheral flange and the basal angulation. Moreover, the spines on the peripheral flange are more numerous and denser. That specimen could belong to a distinct species of Meiersia . In this case, the interspecific variation of the genus would be wider than here described.

The material described by Haas (1953: 35, pl. 2: 27, 28, 33, 34) as? Platyacra (Asperilla) sp., from the Late Triassic of Peru exhibits general characters reminiscent of Meiersia . This would demonstrate a Triassic origin of the genus. However, its poor preservation prevents a safe supraspecific attribution.

Stratigraphic and geographic range.—?Late Triassic, Peru; Late Hettangian, Luxembourg; Late Pliensbachian, Calvados ( France).