Nipteraxis Cossmann, 1916

Harzhauser, Mathias & Landau, Bernard, 2023, The Architectonicidae and Mathildidae (Gastropoda, Heterobranchia) of the Miocene Paratethys Sea-victims of the Miocene Climatic Transition, Zootaxa 5370 (1), pp. 1-74 : 32

Genus Nipteraxis Cossmann, 1916

Type species. Solarium plicatum Lamarck, 1804 , original designation by Cossmann (1916: 167); Eocene, France.

Original diagnosis. “ Forme surbaissée, subbicarénée à la périphérie; ornementation formée de crénelures plutôt subgranuleuses qu’aplaties; sutures canaliculées; au dernier tour il existe une carène périphérique un peu plus saillante que les deux qui l’entourent, mais celle du côté de la base est parfois presque aussi proéminente. Base excavée en cuvette plus ou moins déclive, ornée de rubans élégamment décussés par les stries rayonnantes; vers la périphérie de l’ombilic, ces rubans sont plus proéminents, séparés par de plus larges rainures et les crénelures y apparaissent plus écartées, plus étroites; l’ombilic a ses parois très excavées, finement plissées par les accroissements. Ouverture subpentagonale, rainurée à l’intérieur comme celle de Solarium .” [Low form, sub-bicarinate at periphery; ornamentation made up of rather subgranular and flattened cords; suture canaliculate. Last whorls with slightly more protruding peripheral keel than the two surrounding ones, but on the base it is sometimes almost as prominent. Base bowl-like excavated, adorned with cords elegantly crossed by axial ribs; Towards the periphery of the umbilicus, these cords are more prominent, separated by larger grooves and the crenelles appear more apart, narrower. The umbilicus has very excavated walls, with delicate growth lines. Aperture subpentagonal, grooved inside like that of Solarium ] ( Cossmann 1916: 167).

Revised description. “ Shell small to medium sized (usually around 10 mm), solid. Spherical-lenticular with moderately wide umbilicus (UD ~20–35% of total diameter). Sculpture: Axial (growth lines) sculpture usually weak, on smooth (amalgamated) surfaces of the upper and lower sides in some forms delimiting broad folds. Dorsal side with very strong SSC, 2–3 MCs, in some forms more or less amalgamated. Periphery: UPC and IPC Rand adjoining very broad, prominent LPC, forming a Psilaxis-like tripartite keel. Whorls attached at LPC. Base: usually with 6 spiral cords, increasing in width towards umbilicus; partly amalgamated into broad bands. Innermost coarsely noded delimiting umbilicus. Umbilical wall with axial growth lines without spiral cords.” (Bieler 1985: 94, translated from German) ( Fig. 2 ).

Discussion. Nipteraxis comprises several Eocene species such as N. ammonites ( Lamarck, 1804) , N. bifidus (Deshayes, 1863) , N. bonneti (Cossmann, 1902) , N. dameriacensis (Deshayes, 1863) , N. douvillei ( Cossmann & Pissarro, 1902) , N. gaudryi (Morlet, 1888) and N. intermedius (Deshayes, 1863) , which are all characterized by solid shells with moderately elevated spire, beaded spiral cords of which the SSC is most prominent. These species have a convex base with prominent spiral cords, becoming most prominent towards the wide umbilicus. The UC are prominent and tubercular and delimited from the PUC by a distinct groove. In addition, the periphery is formed by the convex LPC and the weaker and slightly indented IPC, which was called “ sub-bicarinate ” by Cossmann (1916). Although it may be disputable to place Neogene species in an Eocene genus, we do not see sufficient differences for separating the Paratethyan species Nipteraxis deformatus nov. sp. and N. exmoniliferus (Sacco, 1892) from Nipteraxis .

Figures

FIGURE 2. Whorl cross-sections of Architectonicidae genera. All modified after Bieler (1993) except for Simplexollata, Basisulcata and Ammotectonica. Solatisonax? refers to Solatisonax? kostejana (Boettger, 1907), Bold genera are represented in the Paratethys Sea. SSC: subsutural cord, MC: mid cord(s), UPC: upper peripheral cord, LPC: lower peripheral cord, IPC: infraperipheral cord; UC: umbilical crenae; PUC: proxumbilical cord.