Alvania, Risso, 1826

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 97

Alvania sp. A

Figs 25V , 26 A–B

Material. MGUH 33163, MGUH 33164 and an external mould in the unofficially catalogued sample SR.1015 deposited at the Natural History Museum of Denmark.

Occurrence. Lithified top of the Maastrichtian Højerup Member, Tor Formation, at Rødvig and Højerup Church, Stevns Klint.

Description. Spire fairly low and wide. Protoconch low spired with smooth and relatively flattened whorls. Transition to teleoconch apparently rather gradual.

Teleoconch whorls moderately convex with periphery slightly adapical of transition to base. Suture narrow and moderately shallow. Transition to strongly convex base rather gradual. Aperture rounded abapically with strongly developed and smooth varix. Teleoconch sculpture consisting of around 10 strong and sharp-ridged, slightly opisthocyrt and opisthocline transverse ribs per half whorl; ribs fading out abapically at transition to base. Transverse ribs weak on first teleoconch whorl, crossed by weak spiral threads. Adapical suture bordered by beaded collar formed by stronger spiral rib delineated abapically by spiral furrow. Transition to weakly spirally ribbed base marked by another stronger spiral rib. Base covered by up to six or seven very weak spiral ribs, crossed adapically by nearly effaced continuations of transverse ribs.

Measurements. Most complete specimen, MGUH 33163, measures 1.6 mm in height and 1.3 mm in width, consisting of three whorls but lacking top of protoconch.

Remarks. Alvania sp.A resembles the Late Cretaceous Alvania costata ( Wade, 1926) and Alvania tallahatchiensis ( Sohl, 1960) from the U.S.A., but is readily recognized by the spiral rib bordering the base, the restricted spiral sculpture and the beaded spiral rib adapically on the whorl.

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.

FIGURE 26. A–B. Alvania sp. A. Silicone cast of MGUH 33164. Width 1.5 mm. C. Alvania sp. B. Silicone cast of MGUH 33165. Width 0.8 mm. D. Zebina sp., Wax cast of MGUH 33166. Width 0.9 mm. E–H. Ceratia rodvigensis n. sp. E–F. Silicone cast of holotype MGUH 33167. Width 0.8 mm. G–H. Silicone cast of paratype MGUH 33168. Width 0.9 mm. I–J. Ceratia? sp. I. Mould of MGUH 33169. Width 0.9 mm. J. Silicone cast of MGUH 33170. Height 1.1 mm. K. Anchura sp., Silicone cast of MGUH 33171. Width 8.6 mm. L–M. Columbellaria tuberculosa (Binkhorst, 1861). Silicone cast of ØSM.10042-202-a–c. Width 5.2 mm, height 5.9 mm. N. Tylostoma? sp., inner mould MGUH 33172. Width 19.9 mm. O–P. Cassidae genus et sp. indet. Silicone cast and internal mould of ØSM.10042-315-a–b and c, respectively. Width 9.2 and 8.6 respectively. Q–U. Sassia faxense Ravn, 1933. Q. Detail of apex of MGUH 33173. Width of protoconch 1.4 mm. R. Silicone cast of MGUH 33174. Width 6.0 mm. S. Silicone cast of MGUH 33175. Width 6.5 mm. T. Silicone cast of MGUH 33176. Width 7.8 mm. U. Silicone cast of MGUH 33177. Width 5.2 mm. V–X. Hipponix sp. V–W. Internal mould MGUH 33178. Length 23.8 mm, width 19.5 mm. X. Inner mould MGUH 33179. Width 19.1 mm. Y–Z. Eulima? danica Ravn, 1933. Y. Silicone cast of MGUH 33180. Width 2.5 mm. Z. Silicone cast of MGUH 33181. Width 2.0 mm. AE. Eulima? sp., Mould MGUH 33182. Width 1.3 mm.