Cerithiella moltkianum ( Ravn, 1902 )

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 118

Cerithiella moltkianum ( Ravn, 1902)

Figs 28 F–I

1902 Cerithium Moltkianum Ravn : 223–224, pl. 1, fig. 23.

1903 Cerithium Moltkianum Ravn—Ravn : 380, 394–395.

Diagnosis. Protoconch with four whorls, first whorl not inflated, the last with around 15 strongly opisthocline collabral threads per half whorl and a weak spiral thread on upper part. Teleoconch columella lacking fold; siphonal termination evenly rounded; spiral ribs 1 and 2 closer than 2 and 3; base carrying only one primary spiral rib.

Material. MGUH 33210 , MGUH 33211 , ØSM.10042-128, the four informally catalogued specimens with sample numbers SR.295 (2 specimens), SR.303.A–B and SR.637.A–B, and 25 external and in a few cases also internal moulds without number belong to the Cerithium Limestone Member . ØSM.10042-381-a and an external mould informally catalogued by sample number SH.385.B derives from the basal Korsnaeb Member of the Stevns Klint Formation. Those without numbers are all from the collections of the Natural History Museum of Denmark .

Type stratum and type locality. Cerithium Limestone Member at Stevns Klint.

Occurrence. Cerithiella moltkianum ( Ravn, 1902) ranges from the lower Danian Cerithium Limestone Member and up into the Korsnaeb Member. It is moderately common in the southern to northern part of the Stevns Klint exposure. A few additional specimens have been collected by C. Heinberg from the lower Danian ‘dead layer’ at Vokslev, Northern Jutland.

Description. Protoconch turriform multispiral with four convex whorls; first 2 ½ whorls possibly smooth, though this may be due to preservation; first whorl not inflated. Last two protoconch whorls with fairly closely spaced opisthocline and moderately opisthocyrt collabral threads, number of collabral threads approximately 35 per whorl. Last protoconch whorl carrying weak spiral thread located at strongest curvature of collabral threads on upper part of whorl. Transition to teleoconch seemingly rather gradual. Protoconch approximately 1.0 mm high and 0.5 mm wide.

Teleoconch whorls flat sided with a more or less pronounced, sharp keel located slightly above narrow and very shallow abapical suture; height of whorls corresponding to around 38 to 40 % of whorl width. Base weakly convex. Aperture rounded rectangular, abapically continuing out into oblique siphonal canal; outer lip with broad and fairly deep sinus just above keel; columella lacking fold.

Whorl sculpture strong, reticulate, consisting of three primary spiral ribs and a number of slightly weaker axial ribs carrying tubercles at connecting points. Spiral rib 1 not starting before third teleoconch whorl after which it lies closer to spiral rib 2 than 2 lies to the distinctly stronger spiral rib 3 situated on the generally weak keel. Axial ribs numbering between 9 and 10 per half whorl on third teleoconch whorl, terminating just below keel. Number of axial ribs increasing slowly abapically while no secondary spiral ribs are added before the 18 th teleoconch whorl. The base carries a single primary spiral rib slightly below the keel and is succeeded by a wide shallow furrow and densely spaced, weak spiral ribs covering the rest of the base.

Measurements. Largest specimen just over 48 mm high and 9.2 mm in diameter with 23 teleoconch whorls.

Remarks. C. moltkianum ( Ravn, 1902) differs from the diagnostic features of Cerithiella as defined by Gründel (1980) and Nützel (1998) by the lack of columellar folds. Even so the other characters such as the protoconch sculpture clearly indicate a strong relation with this group, and with the general variation in strength and number of columellar folds I do not hesitate to assign it here.

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.