Cerithium, Bruguiere, 1789

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 79

Cerithium sp.

Figs 23 F–H

Material. MGUH 33124, MGUH 33125, MGUH 33126, and two fragmentary specimens without number located in the old collections of the Natural History Museum of Denmark.

Occurrence. It ranges from the Lithified top of the Maastrichtian Tor Formation and up into the lower Danian Korsnaeb Member infilled Thalassinoides burrows in the Cerithium Limestone at Stevns Klint.

Description. Protoconch unknown. Teleoconch whorls flat, separated by narrow suture located immediately abapical to keel ridge. Wide and low varices scattered unevenly on spire, the last occurring approximately opposite aperture on last whorl. Keel carrying two sharply developed ridges, adapical one only visible on last whorl. Base flattened. Aperture relatively small, strongly rounded adaxially against only slightly convex columella; inner lip well developed with strong parietal ridge forming continuation of abapical keel ridge. Columellar fold absent. Teleoconch sculpture on younger whorls consisting of weak transverse ribs crossed by spiral lirae, forming up to five weak, beaded spiral ribs. Adult teleoconch whorls nearly smooth but for fine spiral lirae and a weak spiral band of 40 to 50 tubercles per whorl adjacent to adapical suture. Growth lines slightly opisthocyrt, forming very fine and dense pattern on whorl surface, on adapical keel ridge developing into very fine and dense beading. Base covered by spiral ribs of unequal strength.

Measurements. Largest specimen, MGUH 33124, 10.5 mm in diameter with a last whorl height approximating 13 mm.

Remarks. Because of the flattened and weakly sculptured whorls this taxon is not a Cerithium sensu stricto, but belongs most likely to one of the many subgenera erected for this genus. Its affinity with the genus is clearly seen from the aperture with its distinctly rounded outline, strong parietal lip, nearly centrally placed columella, well developed parietal ridge and rather weakly opisthocyrt growth lines. It is distinguished from the genus Metacerithium Cossmann, 1906 by the presence of varices, the strong parietal ridge and the rather weakly forwardly reaching sinus of the basal growth lines.

Figures

FIGURE 23. A. Arene jakobseni n. sp., Silicone cast of paratype MGUH 33120. Preserved width 8.9 mm. B–E. Ataphrus (Ataphrus) knoesensis n. sp. B–C. Silicone cast of holotype MGUH 33121. Width 4.0 mm. D. Silicone cast of paratype MGUH 33122. Width 4.2 mm. E. Silicone cast of paratype MGUH 33123. Width 3.9 mm. F–H. Cerithium sp. F. Silicone cast of MGUH 33124. Width 10.7 mm. G. Silicone cast of MGUH 33125. Width 9.9 mm. H. Silicone cast of MGUH 33126. Width 10.7 mm. I. Pseudovertagus? sp., Silicone cast of MGUH 33127. Width 1.6 mm. J–K. Striovertagus? sp., Silicone cast of MGUH 33128. Width 2.5 mm. L–O. Cerithidea? sp. L–M. Silicone cast of MGUH 33129. Cast height on figure L 7.4 mm. Cast width on figure M 3.3 mm. N–O. Silicone casts of MGUH 33130. Width 3.7 mm. P–S. Cirsocerithium crassilabris (von Koenen, 1885). P–Q. Silicone casts of MGUH 33131. Width 5.0 mm. R. Lectotype MGUH 865. Upper Palaeocene Lellinge Greensand, Denmark. Height 12.7 mm. Photograph by S. L. Jakobsen. S. Lateral view of MGUH 33132. Upper Palaeocene Lellinge Greensand, Denmark. Width 4.4 mm. T–U. Turritellid genus et sp. indet, Silicone cast of MGUH 33133. Width 1.0 mm. V–W. Turritella cf. plana Binkhorst, 1861. Silicone cast of MGUH 33134. Whorl width at least 17.2 mm. Height of last whorl 17.8 mm. X–Y. Mesalia danica n. sp. X. Silicone cast of holotype MGUH 33135. Width 2.2 mm. Y. Silicone cast of paratype protoconch MGUH 33136. Width 0.7 mm. Z. Mesalia sp., Silicone cast of MGUH 33137. Width 0.6 mm. AE. Tenagodus sp., Silicone cast of MGUH 33138. Width 4.3 mm.