Trituba obliquecostulata ( Kaunhowen, 1898 )

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 121-122

Trituba obliquecostulata ( Kaunhowen, 1898)

Fig. 28S

1898 Cerithium oblique-costulatum nov. sp. Kaunhowen: 62, pl. 6, fig. 4.

1933 Cerithiopsis obliquecostulata n. sp. —Ravn: 52–53, pl. 4, figs 12a–b, 13a–b.

2014 Trituba obliquecostulata ( Ravn, 1933) —Lauridsen & Schnetler: 90–91, fig. 138A–C.

Diagnosis. Protoconch with six to seven convex whorls carrying in excess of 20 fine collabral ribs per whorl. Teleoconch with flattened whorls sculptured by strong and slightly opisthocline transverse ribs and around three very weak, but wide spiral ribs.

Material. The K-Pg boundary strata is represented by specimen MGUH 33219 and six somewhat fragmentary moulds of teleoconch from the uncatalogued old collections at the Natural History Museum of Denmark.

Occurrence. The material here treated derives from the lithified top of the Cretaceous Tor Formation at Rødvig, Stevns. This species is additionally known from the lower Danian (?) bryozoan limestone at Limburg in Holland and from the middle Danian limestone at Faxe, Denmark ( Kaunhowen 1898; Ravn 1933).

Description of boundary material. Protoconch not preserved. Teleoconch moderately slender with flat to slightly concave and weakly keeled whorls. Keel located approximately 1/3 the whorl height from abapical suture. Suture not deep, marked by narrow sutural ramp. Transition from whorl side to weakly convex base abrupt. Whorl subrectangular in cross-section with smooth columella lacking columellar fold. Aperture not known.

Teleoconch whorls carrying between 16 and 20 coarse and sharp-ridged opisthocline and slightly opisthocyrt transverse ribs, becoming less pronounced and more rounded on later whorls. Transverse ribs crossed by three weakly developed spiral ribs; one forming adapical shoulder on whorl, followed by second rib located approximately 1/3 of whorl height from adapical suture. The weak keel carries the third and strongest spiral rib.

Measurements. MGUH 33219 is 2.3 mm high and 1.3 mm wide with six teleoconch whorls.

Remarks. This taxon from the uppermost Maastrichtian chalk at Stevns Klint is somewhat fragmentary, but the teleoconch appears completely in agreement with the middle Danian Cerithiopsis obliquecostulata Ravn, 1933 from Denmark, which is clearly a junior subjective synonym of the only slightly older Cerithium obliquecostulatum Kaunhowen, 1898 from the lower Danian limestone deposits in Holland.

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.