Plesiodiceras muensteri

Plesiodiceras? muensteri (Goldfuss, 1837) Fig. 13 v * 1837 Chama Münsteri nobis – Goldfuss: 204, pl. 138, fig. 7 a, b. ? 1860 Diceras Monsbeliardensis Ctj. – Contejean: pl. 27, figs 12–14. 1959 Plesiodiceras subvalfinense Pčel. sp. n. – Pchelintsev: 47, pl. 1, figs 2–8, text-fig. 12. 1959 Plesiodiceras uzuntaschi Pčel. sp. n. – Pchelintsev: 49, pl. 1, figs 9, 10, text-fig. 13. 1959 Plesiodiceras orthogonale Pčel. sp. n. – Pchelintsev: 50, pl. 2, figs 1–3, text-fig. 14. 1959 Plesiodiceras yailense Pčel. sp. n. – Pchelintsev: 52, pl. 2, fig. 4. 1959 Plesiodiceras kuruuzense Pčel. sp. n. – Pchelintsev: 53, pl. 2, fig. 5, text-fig. 15. 1959 Plesiodiceras koreizense Pčel. sp. n. – Pchelintsev: 54, pl. 2, figs 6–11, text-fig. 16. 1959 Plesiodiceras acutiforme Pčel. sp. n. – Pchelintsev: 57, pl. 3, fig. 1. 1989 Plesiodiceras uzuntaschi Pčelincev, 1959 – Yanin: 162, pl. 6, fig. 1. Diagnosis. Shell approximately 60 mm high, with reniform commissure. Left valve coiled-cylindrical in shape, expanding rather slowly during ontogeny, with distinct anterior sulcus. Right valve operculum-shaped. Both valves coiled, with less than 1.5 whorls clearly traceable. Interior shell characters unknown. Material. Syntypes of Chama muensteri Goldfuss, 1837 (late Kimmeridgian; Kelheim Member, Frankenalb Formation; Kelheim area, Bavaria, Germany): Double-valved specimen (pl. 138, fig. 7 a, b; BSPG AS VII 2075), designated lectotype herein. Two double-valved syntypes with preserved shells (not figured; BSPG AS VII 2076, BSPG AS VII 2077). The fourth syntype is an internal mould of a double-valved specimen (not figured; BSPG AS VII 2078). Measurements and figure numbers. Type locality and stratum. “ Occurs in the Portland stone near Regensburg. ” (Goldfuss 1837: 205; translated from German). Late Kimmeridgian; Kelheim Member, Frankenalb Formation; near Regensburg, Bavaria, Germany. Remarks. Only one double-valved specimen of Chama muensteri was figured by Goldfuss (1837: pl. 138, fig. 7 a, b), and no other specimens were explicitly mentioned in his description of the species. However, the same collection tray contains another three double-valved specimens, two of them with reasonably well preserved shells and the third one an internal mould. We thus treat all four specimens as syntypes, and designate the figured specimen, BSPG AS VII 2075, as the lectotype. In the lectotype, the umbo of the left valve including the attachment surface is broken. The right valve is distinctly coiled but operculate, and the commissure is distinctly higher than long, with a marked anterior sinus. The anterior sulcus in the left valve is relatively deep, separating strongly bulging upper and lower parts of unequal size. Of the two additional shell-preserved specimens, BSPG AS VII 2076 has an incompletely preserved left valve and a slightly ambiguous commissure, but most likely represents P.? muensteri. In contrast, BSPG AS VII 2077 clearly shows the characters of Plesiodiceras valfinense, most notably the quickly expanding, short-conical left valve. The internal mould, BSPG AS VII 2078, is too poorly preserved to be specifically assigned. As discussed above, we consider Plesiodiceras? muensteri as different from Plesiodiceras valfinense, based on its reniform commissure and anterior sulcus, and the more slowly expanding left valve. Given that its interior shell characters remain unknown, its assignment to Plesiodiceras is tentative. Hypelasma fritzlangi sp. nov. described below also lacks the anterior sulcus and distinctly reniform commissure. Plesiodiceras? muensteri (Goldfuss, 1837) does not occur at Saal. Its exact type locality ‘ near Regensburg’ is unknown, but cannot have been far from Saal. Given that it is also the earliest potential Plesiodiceras described and the lectotype had never been photographed, it seems appropriate to discuss this species in the present context. Occurrence. Late Kimmeridgian; Kelheim Member, Frankenalb Formation; Regensburg region, Bavaria, Germany (Goldfuss 1837). Tentatively: Kimmeridgian; Montbéliard, Departement Doubs, France (Contejean 1860). Oxfordian; Crimean Mountains (Yayla Mountains), Crimea, Ukraine (Pchelintsev 1959; Yanin 1989).