Striovertagus, Chavan, 1948

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 80

Striovertagus ? sp.

Figs 23 J–K

Material. Specimen MGUH 33128 is an external mould of the teleoconch.

Occurrence. Lower Danian Cerithium Limestone Member at Skeldervig, Stevns Klint.

Description. Whorls weakly convex, separated by shallow but well marked suture. Whorl height corresponding to less than half the width. Whorl periphery located on lower third of whorl. Transition to convex base gradual. Columella fairly short, weakly concave with no columellar folds. Inner lip rather strong, well defined, smooth. Outer lip thick, flat and sharply cut, inside smooth. Growth lines opisthocline, nearly straight.

Teleoconch sculpture weak, dominated on early whorls by approximately 40 to nearly 60 low and sharp-ridged, weakly opisthocline transverse ribs. Later whorls nearly smooth but for a single spiral thread located approximately a third of the whorl height from adapical suture.

Measurements. MGUH 33128 measures 2.5 mm in width, and consists of the final two whorls.

Remarks. The available specimen is a juvenile, meaning that the aperture has not been fully developed with the characteristic oblique siphonal canal. The generic assignment is consequently only tentative with the possibility that the taxon may turn out to belong somewhere else within the Cerithiidae . Striovertagus ? sp. is closely related to the middle Danian Trypanaxis ? faxensis Ravn, 1933 of Denmark, from which it differs by the nearly absent spiral sculpture and a well developed transverse ribbing. Neither taxon belongs to Trypanaxis Cossmann, 1889 . It resembles the Danian Striovertagus punctifibrum ( Briart & Cornet, 1873) from Belgium, but the whorls are more convex and the transverse sculpture more pronounced.

Figures

FIGURE 23. A. Arene jakobseni n. sp., Silicone cast of paratype MGUH 33120. Preserved width 8.9 mm. B–E. Ataphrus (Ataphrus) knoesensis n. sp. B–C. Silicone cast of holotype MGUH 33121. Width 4.0 mm. D. Silicone cast of paratype MGUH 33122. Width 4.2 mm. E. Silicone cast of paratype MGUH 33123. Width 3.9 mm. F–H. Cerithium sp. F. Silicone cast of MGUH 33124. Width 10.7 mm. G. Silicone cast of MGUH 33125. Width 9.9 mm. H. Silicone cast of MGUH 33126. Width 10.7 mm. I. Pseudovertagus? sp., Silicone cast of MGUH 33127. Width 1.6 mm. J–K. Striovertagus? sp., Silicone cast of MGUH 33128. Width 2.5 mm. L–O. Cerithidea? sp. L–M. Silicone cast of MGUH 33129. Cast height on figure L 7.4 mm. Cast width on figure M 3.3 mm. N–O. Silicone casts of MGUH 33130. Width 3.7 mm. P–S. Cirsocerithium crassilabris (von Koenen, 1885). P–Q. Silicone casts of MGUH 33131. Width 5.0 mm. R. Lectotype MGUH 865. Upper Palaeocene Lellinge Greensand, Denmark. Height 12.7 mm. Photograph by S. L. Jakobsen. S. Lateral view of MGUH 33132. Upper Palaeocene Lellinge Greensand, Denmark. Width 4.4 mm. T–U. Turritellid genus et sp. indet, Silicone cast of MGUH 33133. Width 1.0 mm. V–W. Turritella cf. plana Binkhorst, 1861. Silicone cast of MGUH 33134. Whorl width at least 17.2 mm. Height of last whorl 17.8 mm. X–Y. Mesalia danica n. sp. X. Silicone cast of holotype MGUH 33135. Width 2.2 mm. Y. Silicone cast of paratype protoconch MGUH 33136. Width 0.7 mm. Z. Mesalia sp., Silicone cast of MGUH 33137. Width 0.6 mm. AE. Tenagodus sp., Silicone cast of MGUH 33138. Width 4.3 mm.