Cerithiopsis rosenkrantzi (Ravn, 1933) Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 139-140

Vexillum ? rosenkrantzi n. sp.

Figs 31 D–G

Diagnosis. Protoconch with 3 to 3 ¼ whorls. Teleoconch whorls with around seven strong and generally not sharply ridged costae, which form distinct adapical shoulder.

Derivation of name. In honour of Alfred Rosenkrantz, who collected the material and worked with the Palaeocene gastropod faunas from Greenland and Denmark.

Type material. Holotype MGUH 33261 is an inner and outer mould collected by A. Rosenkrantz 22–28 July 1943 . Paratype MGUH 33262 is an external mould from Skeldervig, while paratype MGUH 33263 is an external mould showing the aperture and collected somewhere between Knøsen and Harvig. Both paratypes were collected by A. Rosenkrantz from the Cerithium Limestone Member .

Additional material. A single external mould lacking number belongs to the Natural History Museum of Denmark.

Type stratum and type locality. The Cerithium Limestone Member of the Rødvig Formation from Skeldervig at Stevns Klint.

Occurrence. The Cerithium Limestone Member along the southern half of Stevns Klint.

Description. Protoconch multispiral, high conical, consisting of 3 to 3 ¼ smooth whorls of relatively low convexity. Suture fairly deep. Protoconch around 0.8 mm high and 0.65 mm wide. Transition to teleoconch abrupt, marked by appearance of transverse ribs.

Teleoconch high fusiform with flattened whorls separated by moderately deep suture marked by slight swelling of subsutural wall of succeeding whorl. Last whorl moderately convex with gradual transition from whorl side to base. Canal short but well developed, turrid-like. Aperture high elongated, corresponding to just over half the shell height; adapically narrowly pointed, while continuing out into short but well developed and wide siphonal canal. Outer lip moderately convex, seemingly lacking teeth or lirae internally. Inner lip smooth except for three centrally placed and distinct columellar folds increasing in strength adapically on slightly curved columella.

Teleoconch sculpture consisting of weak striae subsuturally and on transition to canal, and around seven strong costae per whorl. Costae strongest peripherally on whorl, fading gradually out on adapical part of base and very abruptly at mid-whorl, completely disappearing shortly below adapical suture. This abrupt termination results in a marked pseudo-shoulder around mid-whorl and a flat to weakly concave shoulder slope on an otherwise flat whorl. Growth lines weakly sigmoid, nearly orthogonal on spire whorls.

Measurements. Most complete specimen, paratype MGUH 33262, 6.8 mm high and 3.2 mm wide, consisting of 3 ¼ protoconch whorl and 4 teleoconch whorls.

Remarks. This species differs from the typical members of the genus Vexillum Röding, 1798 by the sparse and exceptionally strong transverse rib sculpture forming a distinct shoulder before fading out close to the adapical suture. The typical costellariid sculpture, at least on early teleoconch whorls, is one of numerous and much finer transverse ribs. The generic assignment is for this reason rather tentative.

Vexillum ? rosenkrantzi n. sp. differs from the slightly younger Turricula sp. sensu Ravn (1933) from the middle Danian of Faxe, Denmark, by the less sharply developed costae with their stronger and more abapical shoulder, and by the apparently slightly shorter canal. It is characterized from the Palaeocene Volutidae , indeterminate sensu Kollmann & Peel (1983: fig. 199) from Greenland by having more rounded costae and a sharper posterior apertural angle.

Figures

FIGURE 31. A–C. Vexillum tenestolidum n. sp. A–B. Silicone cast of holotype MGUH 33259. Width of protoconch 0.7 mm. Width of last whorl 3.4 mm. C. Silicone cast of paratype MGUH 33260. Width 5.8 mm. D–G. Vexillum? rosenkrantzi n. sp. D–E. Silicone cast and inner mould of holotype MGUH 33261. Width 1.9 and 1.6 mm respectively. F. Silicone cast of paratype MGUH 33262. Width 3.2 mm. G. Silicone cast of paratype MGUH 33263. Width 2.9 mm. H. Vexillum? sp. Silicone cast of MGUH 33264. Width 3.5 mm. I. Columbarium heberti (Briart & Cornet, 1880). Silicone cast of last whorl MGUH 33265. Width 7.7 mm. Photograph by S.L. Jakobsen. J. Columbarium sp. Silicone cast of MGUH 33266. Width 13.3 mm. K–N. Conomitra glabra (Ravn, 1902). K. Silicone cast of MGUH 33267. Width 3.6 mm. L–M. Silicone cast of MGUH 33268. Width 3.6 and 3.9 mm respectively. N. External cast of syntype MGUH 116. Height 8.2 mm. Photograph by S.L. Jakobsen. O. Volutomitra cf. quinqueplicata Ravn, 1902. Silicone cast of MGUH 33269. Width 11.6 mm. P. Volutomitra quinqueplicata Ravn, 1902. External cast representing last whorl of type specimen MGUH 117. Middle Danien Faxe Formation, Denmark. Height 38.6 mm. Photograph by S.L. Jakobsen. Q–R. Spirancilla milthersii (Ravn, 1902). Q. Silicone cast of holotype MGUH 33270. Width 3.3 mm. R. Silicone cast of MGUH 33271. Width 3.1 mm. S–T. Exilia sp., Silicone cast of MGUH 33272. Width 1.6 mm. U–W. Latiromitra? sp. External cast and inner mould of MGUH 33273. Width 4.6 mm for casts and 4.0 mm for mould.