Neridomus Morris and Lycett, 1851

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 : 357

Genus Neridomus Morris and Lycett, 1851

Type species: Neridomus anglica Cox and Arkell, 1950 (new name pro Nerita hemisphaerica Morris and Lycett, 1851 , non Roemer, 1836). Bathonian, Minchinhampton ( England).

Remarks.—The species described below are assigned to the genus Neridomus Morris and Lycett, 1851 for the presence of a broad, thick and smooth callus on the inner lip. According to Bandel (2008) this is one of the main characters of the family Neridomidae Bandel, 2008 . Neritaria Koken, 1892 has a shell similar to that of Neridomus . It differs in having a tooth on the inner lip ( Bandel 2007, 2008).

In some specimens (e.g., Figs. 6D 1 , 7A 3 , A 4 ) the callous pad shows a rounded swelling on the axial region of the base which could be interpreted as a tooth−like structure. However, this swelling is much shallower and more rounded than the tooth of Neritaria . Moreover, it is clearly an aspect of intraspecific variability and, most probably it is related to an occasional owergrowth of the callus.

Figures

Fig. 6. Neritimorph gastropod Neridomus liasina (Dunker, 1844) from Brouch (Mersch, Grand−Duchy of Luxembourg), Late Hettangian (Schlotheimia angulata Zone, Schlotheimia complanata Subzone), Early Jurassic. A. MNHNL BR362, dorsal (A1), apertural (A2), subapertural (A3), and apical (A4) views. B. MNHNL BR701−1, dorsal (B1), and apical (B2) views. C. MNHNL BR701−2, dorsal (C1), apical (C2), apertural (C3), and subapertural (C4) views. D. MNHNL BR702, apertural (D1), dorsal (D2), and subapertural (D3) views.E. MNHNL BR882 showing the absence of the inner shell wall by dissolution. F. MNHNL BR877, dorsal (E1), lateral (E2), apical (E3), apertural (E4), and subapertural (E5) views.

Fig. 1. Jurassic geology of Luxembourg.A. Schematic geological map of the Mesozoic units. 1, Palaeozoic basement; 2, Triassic sediments; 3, Luxembourg Sandstone Formation including the Elvingen marl at its base (Hettangian to lowermost Sinemurian); 4, Strassen marl and limestone (Lower Sinemurian to Upper Sinemurian); 5, Ockerkalk Formation (Upper Sinemurian to Pliensbachian); 6, bituminous shale (uppermost Pliensbachian to Toarcian); 7, Minette Irostone Formation (Toarcian–Aalenian); 8, limestone and marl (Lower Bajocian); 9, major fault lines. B. Stratigraphical sketch of the Jurassic succession. 1, dolostone; 2, clay and marl; 3, sandstone; 4, oolitic ironstone; 5, limestone. Map and stratigraphical column redrawn from Service Géologique de Luxembourg (1998). Other data from Boulvain et al. (2000, 2001) and Van den Bril and Swennen (2008).

Fig. 7. Neritimorph gastropod Neridomus cannabis (Terquem, 1855) from Brouch (Mersch, Grand−Duchy of Luxembourg), Late Hettangian (Schlotheimia angulata Zone, Schlotheimia complanata Subzone), Early Jurassic. A. MNHNL BR365, dorsal (A1), apical (A2), apertural (A3), and subapertural (A4) views. B. MNHNL BR878, apertural (B1), lateral (B2), apical (B3), and dorsal (B4) views. C. MNHNL BR879, apertural (C1), dorsal (C2), and apical (C3) views. D. MNHNL BR883, subaxial section showing the absence of the inner shell wall by dissolution.

Fig. 3. Location of the outcrops yielding the material studied here. 1, Brouch (Mersch); 2, Steinfort; 3, Kopstal (Biremdall); 4, Bridel (Birgerkeiz); 5, Mamer (Kaatzefiels); 6, Hespérange; 7, Burmerange. Grey lines, motorways and link motorways; double lines, national roads; single lines, byroads; dashed lines, state boundary.

Fig. 4. Explanatory drawings of gastropod shells morphology. A. Limpetshaped shells, in lateral (A1) and apical (A2) views. B. Trochospiral shells. Abbreviations: H, height of the shell; HA, height of the peristome; HL, height of the last whorl; L, length of the peristome; Lp, distance of the apex from the posterior margin of the peristome; W, width of the base; WA, width of the peristome; α, mean spiral angle.