Rissoina, d'Orbigny, 1840

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 96

Rissoina ? sp.

Figs 25 Q–R

Material. Specimen MGUH 33161 is an external mould of the protoconch and two first teleoconch whorls.

Occurrence. The lower Danian Cerithium Limestone Member , 20 to 25 cm above the base of the Rødvig Formation at Højerup Church, Stevns Klint.

Description. Protoconch conical, just over 0.4 mm high and 0.45 mm wide, consisting of 3 ½ smooth, weakly convex whorls. Transition to teleoconch relatively sharp.

Teleoconch whorls weakly convex, twice as wide as high with periphery located immediately adapically of deeply impressed linear suture. Teleoconch whorls carrying strong and closely spaced, nearly straight transverse ribs, number of ribs 20 or just below on first teleoconch whorl.

Measurements. Specimen MGUH 33161 is 1.15 mm high, consisting of five whorls with a 0.6 mm wide penultimate whorl.

Remarks. The material does not allow for a closer taxonomical identification, but the general protoconch outline and the teleoconch with its well defined transverse ribs on weakly convex whorls separated by deeply impressed sutures supports a placement within this genus. It differs from the Cretaceous Zebinella selandica n. sp. described below by a more conical protoconch and the slightly coarser and straighter transverse ribs.

Figures

FIGURE 25. A–G. Natica sp. A. A–B. Silicone cast of MGUH 33154. Width 7.9 mm. C–D. Silicone cast of MGUH 33155. Width 1.4 mm. E–G. Silicone cast of MGUH 33156. Width 2.1 mm. H–I. Natica sp. B. Silicone cast of MGUH 33157. Width 2.3 mm. J–N. Polinices sp. A. J–L. Silicone cast of MGUH 33158. Width 3.0 mm. M–N. Silicone cast of MGUH 33159. Width 5.2 mm. O–P. Polinices? sp. B. Silicone cast of MGUH 33160. Width 5.0 mm. Q–R. Rissoina? sp., Silicone cast of MGUH 33161. Width 0.6 mm. S–U. Zebinella selandica n. sp., Silicone cast of holotype MGUH 33162. Width 0.8 mm. Width of protoconch 0.55 mm. V. Alvania sp. A. Silicone cast of MGUH 33163. Width 1.2 mm.