Eucycloscala gracilicostatus, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 71

Eucycloscala gracilicostatus n. sp.

Figs 21 R–T

Diagnosis. Spire whorls rounded, not angular. Lamellar to cord-like transverse ribs present within half a whorl from the protoconch. Later whorls also with sharp spiral ribs, forming strong reticulate pattern with transverse ribs.

Derivation of name. In reference to the delicate ribbing of the teleoconch.

Type material. Holotype MGUH 33108 is an external mould of the spire . Paratype MGUH 33107 is an external mould of the transition from periphery to base. The paratype comes from the same locality and stratigraphic level as the holotype .

Additional material. The informally numbered SR.809, SR.993.A–B and D, SR.1116, and a mould lacking number, all from the collections of the Natural History Museum of Denmark.

Type stratum and type locality. Lithified top of the Maastrichtian Højerup Member at Rødvig, Stevns Klint.

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

Description. Protoconch low heterostrophic with approximately 1 ¼ smooth and strongly convex whorls and deep suture. Height measuring nearly 0.2 mm, while width reaches 0.4 mm. Transition to teleoconch sharp.

Teleoconch turbiniform with three strongly convex whorls and deep suture located just adapically of strongly angular transition to flattened base of preceding whorl. Aperture not known. First teleoconch whorl covered by 14 lamellar and slightly prosocline transverse ribs, the rib number increasing slowly on later whorls. Transverse ribs crossed by two to four sharply defined spiral cords, forming spiny tubercles at connecting points. Angle between whorl side and base of last whorl carrying yet another strong spiral cord. Whorl base with at least one strongly developed spiral rib and no transverse ribs.

Measurements. Holotype MGUH 33108 composed of just over four whorls and measuring 2.3 mm in width and over 2.0 mm in height.

Remarks. Eucycloscala gracilicostatus n. sp. resembles the middle Danian Eucycloscala ultima Ravn, 1933 from Denmark but for the strongly developed spiral cords on the later whorls. It differs from the Campanian Eucycloscala cretacea Kiel & Bandel, 2001b from Spain by the strongly rounded, non-angular spire whorls, a first teleoconch whorl not flattened around the protoconch, and by the sharp ribs.

Figures

FIGURE 21. A–B. Leptomaria meyeri Pacaud, 2004. Silicone cast and inner mould of MGUH 33097. Width of cast 14.5. Width of inner mould 11.4 mm. C–H. Bathrotomaria jakobseni n. sp. C–F. Silicone cast and inner mould of holotype MGUH 33098. Width of exposed shell 21.3, 21.3, 15.6, 17.3 mm respectively. G. Outer mould of paratype MGUH 33099. Preserved radius 4.4 mm. H. Silicone cast of last whorl of paratype MGUH 33100. Width 16.2 mm. I. Bathybembix? sp., Silicone cast of MGUH 33101. Width 3.65 mm. J–K. Danilia sp., Silicone cast of MGUH 33102. Width 1.25 mm. L–Q. Chilodonta rudis (Binkhorst, 1861). L–M. Silicone cast of MGUH 33103. Width 6.0 mm for complete specimen, 0.25 mm for protoconch. N–O. Silicone cast of MGUH 33104. Width 7.35 mm. P. Silicone cast of aperture MGUH 33105. Height 4.8 mm. Q. Silicone cast of MGUH 33106. Width 4.65 mm. R–T. Eucycloscala gracilicostatus n. sp. R. Silicone cast of paratype MGUH 33107. Width of fragment 1.3 mm. S–T. Silicone cast of holotype MGUH 33108. Width 2.3 mm. U. Phorcus sp., Silicone cast of MGUH 33109. Height 3.2 mm, exposed width 2.2 mm.