Ataphrus (Ataphrus) knoesensis Hansen 2019, n. sp.

Ataphrus (Ataphrus) knoesensis n. sp.

Figs 23 B–E

2014 Ataphrus (Ataphrus) sp. Hansen & Surlyk: 339, fig. 6: 6, tab. 3.

Diagnosis. Shell with convex spire, flattened top, no umbilicus and a relatively strong spiral sculpture.

Derivation of name. In reference to the type locality Knøsen at Stevns Klint.

Type material. Holotype MGUH 33121 is an external and internal mould. Paratype MGUH 33122 is an external and part of internal mould from Stevns Klint, while paratype MGUH 33123 is an external mould from Holtug, Stevns Klint.

Additional material. ØSM.10042-253-c–d, the informally catalogued specimens SR.753.A–B, SR.757, SR.785.A–B, SR.971, SR.981, SR.983, SR.1018, SR.1071.A, SR.1108.A, and a mould without number placed in the old collections of the Natural History Museum of Denmark.

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

Occurrence. Uppermost Maastrichtian at Stevns Klint in Denmark, where it has been collected from the lithified top of the Tor Formation at Holtug Quarry, Knøsen, Rødvig and in the cove at Boesdal.

Description. Shell globosely turbiniform. Protoconch flattened paucispiral to planispiral, approximately 0.6 mm wide, consisting of two whorls; surface nearly smooth but for faint spiral ribs, which slowly increases in number and distinctiveness. Transition to teleoconch gradual.

Teleoconch whorls evenly rounded with very faint keel. Base slightly flattened. Last whorl distinctly downturned with strong suture passing down below keel of preceding whorl. Surface covered by weak collabral threads and moderately weak spiral threads, which become slightly stronger around keel.

Measurements. Largest specimen, holotype MGUH 33121, is 4.4 mm wide and 4.5 mm high.

Remarks. Ataphrus (Ataphrus) knoesensis n. sp. differs from most species within this subgenus in the presence of spiral sculpture. It closely resembles the contemporaneous Ataphrus (Ataphrus) compactus Gabb, 1869 from California, which has been refigured by Stewart (1927), but the abapical turn of the last whorl appears more pronounced, the base is not as convex with a sharper transition to the whorl flank, and the spiral threads are coarser and slightly stronger, especially around the keel. This species is distinguished from Ataphrus sp. sensu Kollmann & Peel (1983) from the Palaeocene of Greenland by the weaker keel, slightly stronger whorl inflation and a distinctly downturned last whorl. It is distinguished from the Jurassic A. (A.) marschmidti Gründel & Kaim (2006) from Poland in the lack of an umbilicus, stronger spiral threads and more convex spire.