Mathilda dania, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 163-164

Mathilda dania n. sp.

Figs 35 E–I

Diagnosis. Protoconch smooth, nearly perpendicular to teleoconch axis. Teleoconch moderately slender with ap- proximately 50 thin transverse ribs and three to four coarser, slightly less densely spaced spiral ribs adapical of keel. Keel situated one quarter the whorl height from abapical suture.

Derivation of name. Refers to the Danian age and its Danish origin.

Type material. Holotype MGUH 33308 is a nearly complete external mould . Paratype MGUH 33309 is an external mould and comes from the Cerithium Limestone Member at Skeldervig . Paratype MGUH 33310 is a protoconch from 20 to 25 cm above the K-Pg boundary at Højerup, while the protoconch paratype MGUH 33311 was found 42 to 52 cm above the K-Pg boundary at Rødvig . Paratype MGUH 33312 is an external mould of the spire from Vokslev , Northern Jutland .

Additional material. ØSM.10042-89-c–d, 10 specimens with the informal sample numbers SH.294.A–C, SH.398, SH.446, SH.499.A–B, SR.476.A, SR.624, SR.631, SR.641, SR.668.B and SO.189, and 3 more or less fragmentary moulds without numbers from the uncatalogued old collections at the Natural History Museum of Denmark .

Type stratum and type locality. Cerithium Limestone Member of the Rødvig Formation at Holtug, Stevns Klint.

Occurrence. Middle to upper part of the Cerithium Limestone Member of the Rødvig Formation and basal Korsnaeb Member of the Stevns Klint Formation. This species has been found at Rødvig, Skeldervig, Højerup and at Holtug, all localities at Stevns Klint. Additionally it occurs in material collected by C. Heinberg from the contemporaneous ‘dead layer’ in Vokslev Quarry, Northern Jutland.

Description. Protoconch hyperstrophic, diverging about 125˚ from teleoconch axis, smooth with sharp transi- tion to teleoconch.

Teleoconch slender, conical; whorls with strong keel ¼ the whorl height from rather indistinct abapical suture; whorl sides flattened to slightly concave adapically and abapically to keel. Last whorl taking up 40 % of shell height. Base with weaker keel, abapically flattened. Aperture rounded, sub-rectangular with slightly thickened lip. Teleoconch sculpture on first whorl consisting of densely spaced weak transverse ribs and three to four spiral ribs, the one on the keel being the strongest. Number of spiral and transverse ribs increasing abapically on shell, the spiral ribs reaching a number of five to six moderately coarse ribs. Transverse ribs numbering around 50 on fourth whorl. Base, except for strong spiral rib on abapical keel, nearly smooth or carrying weak spiral ribs and faint transverse ribs.

Measurements. Holotype MGUH 33308 is 4.3 mm high and 1.7 mm wide with 5 ½ teleoconch whorls.

Remarks. Mathilda dania n. sp. resembles the Selandian Mathilda carinata ( Ravn, 1939) from Denmark, but has distinctly less convex whorls with a stronger keel and fewer strong spiral ribs abapical to the keel. It differs from the Danian Mathilda unicarinata ( Ravn, 1933) from Denmark by having only two spirals above the carina on the early whorls.

Figures

FIGURE 35. A–B. Pseudomalaxis sp., Silicone cast of MGUH 33306. Width 4.3 mm. C–D. Climacopoma? sp., Silicone cast of MGUH 33307. Width 13.1 and 9.9 mm respectively. E–I. Mathilda dania n. sp. E. Silicone cast of holotype MGUH 33308. Width 1.9 mm. F. Silicone cast of paratype MGUH 33309. Width 2.0 mm. G. Silicone cast of paratype MGUH 33310. Width 0.8 mm. H. Silicone cast of paratype MGUH 33311. Width 0.7 mm. I. Silicone cast of paratype MGUH 33312. Width 1.7 mm. J–K. Clathrobaculus sp., Silicone cast of MGUH 33313. Width 0.5 mm. L–P. Ringicula sp. L. Silicone cast of MGUH 33314. Width 7.0 mm. M–N. Silicone cast of MGUH 33315 and a partly hidden second specimen. Width 7.3 and 6.6 mm respectively. O–P. Silicone cast of MGUH 33316. Width 5.6, 5.3 mm respectively. Q–T. Cylichna stevniensis n. sp. Q. Silicone cast of holotype MGUH 33317. Width 1.4 mm. R–S. Internal mould of paratype MGUH 33318. Width 1.5 mm. T. Internal mould of paratype MGUH 33319. Width 2.8 mm. U–V. Cylichna? sp. A. Cast of MGUH 33320. Width 2.3, 2.4 mm respectively. W–Y. Cylichna? sp. B. W. Wax cast of MGUH 33321. Width 2.4 mm. X–Y. Inner mould of MGUH 33322. Width 1.3 mm. Z–AE. Roxania sp. Cast of MGUH 33323. Width 3.2, 3.3 mm respectively.