Ageria skeldervigensis, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 123

Ageria skeldervigensis n. sp.

Figs 28 X–Y, 29A–B

Diagnosis. Early teleoconch whorls strongly and fairly densely sculptured by sharp transverse ribs mostly lacking tubercles; last whorl widening with base contour shifting from flat to strongly convex.

Derivation of name. Refers to the type locality Skeldervig at Stevns Klint.

Type material. The holotype MGUH 33226 is a nearly complete external mould without protoconch . Paratype MGUH 33224 is from the Højerup Member at Rødvig , while paratype MGUH 33225 comes from the Højerup Member north of Kulsti Rende, Stevns Klint .

Additional material. A mould in the informally catalogued sample SO.5.A, and a fragmentary external and internal mould from the uncatalogued old collections at the Natural History Museum of Denmark.

Type stratum and type locality. The lithified top of the Maastrichtian Højerup Member at Skeldervig, Stevns Klint.

Occurrence. This species is known exclusively from the lithified top of the upper Maastrichtian Højerup Member of the Tor Formation at Rødvig, Skeldervig and north of Kulsti Rende, Stevns Klint.

Description. Protoconch unknown. Teleoconch slender turriculate, with evenly increasing whorl width; whorls weakly convex, separated by narrow suture; whorl height corresponding to half or slightly more than half the width. Transition to smooth flat base sharp, marked by weak carina. A second weaker carina may appear on base of adult specimens. Base on early whorls flattened, becoming more convex with growth. Columella smooth. Aperture unknown.

Teleoconch sculpture dominated by coarse and weakly opisthocline transverse ribs; rib number increasing gradually with growth from around 14 on initial teleoconch whorls. Rare large and low, weakly developed varices occur, becoming slightly more common on later whorls. A more or less distinctly developed spiral rib and succeeding furrow occur adjacent to adapical suture. Interspaces between transverse ribs characterized by an additional five secondary and very weak spiral ribs. Later whorls smooth but for weak spiral lirae crossed by fine, opisthocyrt and slightly opisthocline growth lines. Base with slightly stronger spiral lirae.

Measurements. Holotype MGUH 33226 is 4.5 mm wide and 14.4 mm high, consisting of 14 ½ teleoconch whorls.

Remarks. The Danish late Maastrichtian Ageria skeldervigensis n. sp. resembles the Maastrichtian A. weeksi Wade, 1926 from the Ripley Formation of southern United States, but is distinguished by the higher number of tubercle rows on the later whorls and the apparently two and not three smooth protoconch whorls. It differs from the Maastrichtian Ageria gankinensis Kaim et al., 2004 from northern Russia by the more convex base and a finer teleoconch sculpture with weaker tubercles. It is furthermore distinguished from the two British late Albian species A. gaultina Abbass, 1973 and A. costata ( Sowerby, 1827) by the distinctly less pronounced spiral ribs and growth line sculpture and by a slightly more convex base. Ageria skeldervigensis n. sp. may resemble Ageria laxa n. sp. described below from the succeeding Cerithium Limestone Member , but differs by the nearly effaced tubercles on each transverse rib; a relatively early disappearance of the teleoconch sculpture and by a generally slightly higher number of transverse ribs per whorl.

Figures

FIGURE 28. A. Thereitis carlsbergi n. sp., Protoconch of paratype MGUH 33205.Width of protoconch 0.4 mm. B–D. Thereitis cretacea n. sp. B. Holotype protoconch MGUH 33206. Width 0.4 mm. C. Silicone cast of paratype MGUH 33207. Width 0.9 mm. D. Silicone cast of paratype MGUH 33208. Width 1.1 mm. E. Thereitis sp., Silicone cast of MGUH 33209. Width 0.4 mm. F–I. Cerithiella moltkianum (Ravn, 1902). F–H. Silicone cast of MGUH 33210. Width of teleoconch 4.6 mm. Height of protoconch 1.0 mm. I. Silicone cast of MGUH 33211.Width 9.2 mm. J–O. Cerithiella selandica n. sp. J–K. Silicone cast of holotype MGUH 33212. Teleoconch width 2.6 mm. Preserved protoconch width 0.5 mm. L–M. Silicone cast of paratype MGUH 33213. Height 31 mm. N. Paratype protoconch MGUH 33214. Width 0.7 mm. O. Silicone cast of paratype MGUH 33215. Width 2.6 mm. P–Q. Cerithiella sp. P. Silicone cast of MGUH 33216. Width 6.7 mm. Q. Silicone cast of MGUH 33217. Width 5.1 mm. R. Eumetula sp., Silicone cast of MGUH 33218. Width 0.9 mm. S. Trituba obliquecostulata (Kaunhowen, 1898). Silicone cast of MGUH 33219. Width 1.2 mm. T–V. Vatopsis heinbergi n. sp. T. Silicone cast of holotype MGUH 33220. Width 1.2 mm. U. Silicone cast of paratype MGUH 33221. Width 3.1 mm. V. Silicone cast of paratype MGUH 33222. Width 4.0 mm. W. Vatopsis sp., Silicone cast of MGUH 33223. Width 2.5 mm. X–Y. Ageria skeldervigensis n. sp. X. Silicone cast of paratype MGUH 33224. Height 4.1 mm. Y. Silicone cast of paratype MGUH 33225. Width 7.4 mm.