Kroisbachia, Traub, 1989

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 158

Kroisbachia sp.

Fig. 34F

Material. One mould, MGUH 33299.

Occurrence. The Cerithium Limestone Member at Skeldervig, Stevns Klint.

Description. Protoconch obtusely conical, 1.0 mm wide and 0.75 mm high, consisting of around 2 ¾ smooth and moderately convex whorls.

Teleoconch subfusiform to ovoid-conical with an H/W ratio of around 1.3. Last whorl corresponding to nearly 80 % of shell height. Whorls moderately to weakly convex with a narrow subsutural ramp and a whorl periphery located immediately adapical to deep abapical suture. Aperture subrectangular, the height corresponding to nearly 2/3 of shell height. Columella moderately long, slightly curved, carrying three strong columellar folds. Siphonal canal short.

Teleoconch sculpture composed of weak spirals, strongest adapically around shoulder. Spirals crossed by up to around 35 weak prosocline transverse ribs or growth lines per whorl; ribs fading out at transition to base.

Measurements. The available specimen MGUH 33299 is more than 3.4 mm high and 2.7 mm wide, consisting of protoconch and two teleoconch whorls.

Remarks. This taxon is clearly distinguished from the Selandian Kroisbachia conoidea ( von Koenen, 1885) from Denmark by the relatively larger aperture and stronger columellar folds. It has more resemblance to the Selandian K. peeli Schnetler & Petit, 2010 from Greenland, from which it differs by the stronger columellar folds and higher protoconch whorl number. It differs from the Palaeocene K. haunsbergensis Traub, 1989 from Germany by the absence of well developed spiral ribs on the base and by the much denser transverse ribbing.

Figures

FIGURE 34. A–E. Admetula sp. A–D. Silicone cast and internal mould of MGUH 33297. Widths 6.6, 7.2, 7.0 and 6.1 mm respectively. E. Internal mould of MGUH 33298. Width 5.6 mm. F. Kroisbachia sp., Silicone cast of MGUH 33299. Width 2.4 mm. G. Mataxa s.l. sp., Silicone cast of MGUH 33300. Width 3.9 mm. H–I. Neogastropoda genus et sp. indet., Silicone cast of MGUH 33301. Width 0.7 mm. J–N. Ravniella danica (Ravn, 1902). J–K. Silicone cast of MGUH 33202. Widths 4.7 and 4.3 respectively. L. Silicone cast of lectotype MGUH 126. Width 4.3 mm. Photograph by S.L. Jakobsen. M–N. Silicone cast of MGUH 33303. Width 4.1 and 3.8 mm. O–S. Disculus selandicum (Ravn, 1902). O. Silicone cast of MGUH 33304. Width 8.7 mm. P–Q. Silicone cast of paralectotype MGUH 80 figured by J.P.J. Ravn (1902, Pl. I: 6). Width 7.1, 6.9 mm respectively. R. Silicone cast of lectotype MGUH 79. Width 6.0 mm. Photograph by S.L. Jakobsen. S. Silicone cast of MGUH 33305. Width 5.9 mm.