Ptychomphalus caepa ( Eudes−Deslongchamps, 1849 ), MNHNL BR

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 : 369-371

Ptychomphalus caepa ( Eudes−Deslongchamps, 1849)

Fig. 13 .

1849 Pleurotomaria coepa [sic] sp. nov.; Eudes−Deslongchamps 1849: 150–151, pl. 17: 4a, b.

1854 Pleurotomaria coepa [sic] Eudes−Deslongchamps; Orbigny 1854: 399–400, pl. 348: 1, 2.

1855 Pleurotomaria caepa Eudes−Deslongchamps ; Terquem 1855: 272, pl. 26: 2a–c.

1970 Ptychomphalus rotellaeformis (Dunker) ; Gaetani 1970: 389–390, pl. 31: 1–4.

1997 Ptychomphalus caepa (Eudes−Deslongchamps) ; Fischer and Weber 1997: 155, pl. 25: 13, 14.

Material.— Two specimens: MNHNL BR 462, MNHNL BR 682−1, Brouch, Upper Hettangian ( Schlotheimia angulata doi:10.4202/app.2010.0098

Zone, Schlotheimia complanata Subzone ). Five specimens: MNHNL BR810 (two specimens), MNHNL BR826 (two specimens), MNHNL BR830 , Brouch, Lower Hettangian ( Psiloceras planorbis Zone , Caloceras beds). Fourteen specimens: MNHNL GL213 (eleven specimens), MNHNL GL426 (three specimens), Bridel quarry (Birgerkreiz), Luxembourg Sandstone Formation, exact stratigraphical level unknown. Five specimens: MNHNL GL271 (four specimens), MNHNL GL449 , Steinfort, Luxembourg Sandstone Formation, exact stratigraphical level unknown. One specimen: MNHNL GL422 , Kopstal (Biremdall), Luxembourg Sandstone Formation, Lower to Middle Hettangian. One specimen: MNHNL HE188 , Mamer (Kaatzefiels), Strassen marl and limestone, lowermost Sinemurian ( Coroniceras [ Arietites ] bucklandi Zone, Belemnites brevis beds) .

Dimensions.—See Table 2.

Description.—Obtusely conical shell with cyrtoconical outline of the spire. Teleoconch composed of about six smooth whorls. Periphery smoothly angulated. Surface of whorls slightly concave, becoming slightly convex in the last growth stage. Suture not impressed. Peripheral angulation not exposed on spire. Selenizone scarcely visible, flush and moderately wide, running at the upper edge of periphery and not exposed on the spire. Slit short. Base convex and swollen, cryptomphalous. Aperture subcircular, with a marked sutural corner. Peristome discontinuous on the parietal lip. Inner lip arched, smoothly passing to the basal lip and provided with a strong callus. Callus extended greatly to the umbilical cavity and forming a large, circular, smooth pad which fills the wide umbilicus. Ornament made of a smooth, bulge−shaped subsutural carina appearing early during the growth. Whorl surface otherwise smooth. Base smooth. Selenizone bordered by thin marginal spiral threads. Growth lines faint, prosocline and prosocyrt on the spire, prosocyrt below the selenizone, opisthocyrt on the base, becoming prosocyrt on its axial region.

Remarks.— Eudes−Deslongchamps (1849: 150) erroneously established the name of the species as Pleurotomaria coepa Eudes−Deslongchamps, 1849 , intending to refer to the Latin translation of the term “onion”. Terquem (1855) corrected the name of the species, since its correct Latin spelling is caepa . This is also in accordance with Articles 32.5 and 33.2 (Comma 33.2.2) of the ICZN (1999). According to Fischer and Weber (1997), the holotype of P. caepa has been lost. Thus, they designated a neotype and a paraneotype, based on the two specimens figured by Terquem (1855).

The analysis of the rich material from Luxembourg allows to recognise the ontogenetic characters and the variability of the species. The juvenile specimens have a relatively depressed spire and, consequently, the shell tends to have a lenticular shape. During the adult growth, the shell becomes obtusely conical, although the height of the spire is variable. The sutural bulge can be also variably prominent, but it is always distinct. In some specimens, it becomes feebly and irregularly undulated during the adult growth, without forming distinct nodes.

Ptychomphalus caepa differs from Ptychomphalus rotellaeformis ( Dunker, 1847) in having a higher spire. Consequently, the shape of the shell is less lenticular. Moreover, the peripheral angulation is more distinct than in P. rotellaeformis and the suture is marked by a spiral bulge.

Ptychomphalus compressus ( Sowerby, 1812) ( Sowerby 1812: 33, pl. 10) differs from P. caepa in having more rounded whorls. The selenizone is elevated and forms a peripheral thread whereas in P. caepa the selenizone is flush.

Stratigraphic and geographic range.—Hettangian ( Alsatites liasicus to Schlotheimia angulata Zones ), Hettange−Grande (Lorraine, France); Hettangian, Dalheim ( Luxembourg); Early Hettangian ( Psiloceras planorbis Zone ) and Late Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ), Brouch ( Luxembourg); Late Hettangian, Lombardy ( Italy).

Figures

Fig. 13. Ptychomphalid gastropod Ptychomphalus caepa (Eudes−Deslongchamps, 1849) from Brouch (Mersch, Grand−Duchy of Luxembourg), Late Hettangian (Schlotheimia angulata Zone, Schlotheimia complanata Subzone), Early Jurassic. A. MNHNL BR213−1, apertural (A1), lateral (A2), dorsal (A3), basal (A4), and apical (A5) views. B. MNHNL BR810−1, apertural (B1), basal (B2), apical (B3), and dorsal (B4) views. C. MNHNL BR826−1, dorsal view. D. MNHNL BR213−2, dorsal (D1), apical (D2), basal (D3), and apertural (D4) views.