Mesalia danica, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 84-85

Mesalia danica n. sp.

Figs 23 X–Y

2014 Mesalia sp. Hansen & Surlyk: tab. 3.

Diagnosis. Protoconch broad and low with four whorls. Teleoconch spire relatively low with weakly beaded spiral ribs and a smooth, flattened base.

Derivation of name. danica (Latin) =Danish.

Type material. Holotype MGUH 33135 is a well preserved external mould of the protoconch and teleoconch spire . Paratype MGUH 33136 is an external mould of the protoconch from the same stratigraphic level at Højerup, Stevns Klint .

Additional material. Two fragmentary external moulds from the uncatalogued old collections at the Natural History Museum of Denmark, and a complete external mould ( ØSM.10042-335-a and b) from the collections at Østsjaellands Museum.

Type stratum and type locality. Lithified top of the Højerup Member of the upper Maastrichtian Tor Formation at Holtug Quarry, Stevns Klint .

Occurrence. Lithified top of the Tor Formation at Højerup Church, Mandehoved and Holtug, Stevns Klint.

Description. Protoconch low conical, consisting of four smooth whorls with a very tiny initial chamber. Height and width equal, measuring between 0.5 and 0.6 mm.

Teleoconch whorls sharply convex with flattened upper shoulder and keel-like periphery. Shoulder carrying three to four secondary spiral ribs, followed by three primary spiral ribs intercalated by two secondary ones around the keel. Spiral ribs crossed by strong opisthocyrt growth lines forming weak, diffuse tubercles at connecting points. Broad growth line sinus located just above keel. Base flattened, smooth. Aperture rounded subrectangular.

Measurements. Shell height of MGUH 33135 larger than 4.2 mm and width larger than 2.3 mm.

Remarks. Mesalia danica n. sp. differs from other species of this genus by the broad and low protoconch with its four whorls; the relatively compact teleoconch shell and the weakly beaded spiral ribs. It shows some resemblance to the slightly younger Mesalia instabilis ( Briart & Cornet, 1873) from the Danian of Belgium, but is separated by the more compact shell with a higher number of spiral ribs and a smooth, flattened base. Mesalia danica n. sp. differs from the Danian M. virginiae Stilwell et al., 2004 from Antarctica and the Middle Palaeocene Mesalia sp. 1 and Mesalia sp. 2 sensu Kollmann & Peel (1983) from West Greenland by the convex whorls with weak tuberculation. It is distinguished from the Maastrichtian M. (Woodsalia) jovisammonis ( Quaas, 1902) from Libya by the more compact shell with its tuberculated spiral ribs.

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.