Admetula, Cossmann, 1889

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 157

Admetula sp.

Figs 34 A–E

Material. Two fragmentary moulds, MGUH 33297 and MGUH 33298, the latter preserved as an amalgamation of an internal and external mould due to early dissolution of the shell surface.

Occurrence. The Cerithium Limestone Member south of Stevns Fyr and north of Holtug Quarry, Stevns Klint.

Description. Protoconch somewhat dome-like obtusely conical, with a small beginning and consisting of 1 ½ to 2 ½ convex whorls. Transition to teleoconch gradual, at least on the inner mould.

Teleoconch thin-shelled, ovoid-conical with moderately convex whorls separated by impressed suture. Spire whorls less than half as high as wide, characterized by narrow but distinct subsutural ramp. Aperture moderately narrow; outer lip with 6 or 7 teeth and in some strengthened by weak varix. Short columella with 3 strong columellar folds.

Teleoconch sculpture dominated by unevenly weak spiral threads or bands, separated by narrower grooves and increasing in number with whorl size. Shoulder ramp demarcated by stronger spiral band, which may be separated from adapical suture by up to four weaker threads on final whorls. Spirals crossed by prosocline and opisthocyrt growth lines curving strongly forward adapically. At times growth stops form weak collabral threads, resulting in a weakly reticulate sculpture. Weak varices present but unevenly distributed.

Measurements. The best preserved specimen MGUH 33297 is 7.7 mm wide and close to 12.5 mm high, but lacks the apex.

Remarks. This taxon is morphologically similar to the Palaeocene Admetula eivindi Schnetler & Petit, 2010 from Greenland, but is distinguished through the strength of the more obtuse protoconch, a less marked shoulder ramp, stronger columellar folds and by the presence of varices. It differs from the Selandian Kroisbachia conoidea ( von Koenen, 1885) and Admetula latesulcata ( von Koenen, 1885) , both from Denmark, by the much narrower aperture and stronger columellar folds.

Figures

FIGURE 34. A–E. Admetula sp. A–D. Silicone cast and internal mould of MGUH 33297. Widths 6.6, 7.2, 7.0 and 6.1 mm respectively. E. Internal mould of MGUH 33298. Width 5.6 mm. F. Kroisbachia sp., Silicone cast of MGUH 33299. Width 2.4 mm. G. Mataxa s.l. sp., Silicone cast of MGUH 33300. Width 3.9 mm. H–I. Neogastropoda genus et sp. indet., Silicone cast of MGUH 33301. Width 0.7 mm. J–N. Ravniella danica (Ravn, 1902). J–K. Silicone cast of MGUH 33202. Widths 4.7 and 4.3 respectively. L. Silicone cast of lectotype MGUH 126. Width 4.3 mm. Photograph by S.L. Jakobsen. M–N. Silicone cast of MGUH 33303. Width 4.1 and 3.8 mm. O–S. Disculus selandicum (Ravn, 1902). O. Silicone cast of MGUH 33304. Width 8.7 mm. P–Q. Silicone cast of paralectotype MGUH 80 figured by J.P.J. Ravn (1902, Pl. I: 6). Width 7.1, 6.9 mm respectively. R. Silicone cast of lectotype MGUH 79. Width 6.0 mm. Photograph by S.L. Jakobsen. S. Silicone cast of MGUH 33305. Width 5.9 mm.