Pseudotoma danica, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 151-152

Pseudotoma danica n. sp.

Figs 32 O–S

Diagnosis. Protoconch obtusely conical with slightly less than three smooth whorls. Teleoconch with subsutural spiral cord and constriction and in general around 15 to 18 short and sharp transverse ribs per whorl.

Derivation of name. Name refers to Denmark from where it is known.

Type material. The holotype, MGUH 33283 , is a nearly complete external mould collected by A. Rosenkrantz on 18 July 1940 . Paratype MGUH 33284 was collected from the Cerithium Limestone Member between Knøsen and Harvig , while paratype MGUH 33285 was found in the same bed at Skeldervig .

Additional material. 15 moulds with informal sample numbers SH.184.A, SH.192.A, SH.194.A–B, SH.293. A, SH.452, SR.310.A–B (2 specimens), SR.365.A–B, SR.274, SR.403.A–B, SR.513, SR.515, SR.625, SR.689. A–B, DN.2, and 21 more or less fragmentary moulds from the uncatalogued old collections of the Natural History Museum of Denmark have been examined from the Cerithium Limestone Member at Stevns Klint.A single external fragmentary mould, ØSM.10042-272-b, is known from the Maastrichtian Højerup Member at Stevns Klint .

Type stratum and type locality. Cerithium Limestone Member from the fourth Cerithium Limestone trough south of the old church at Højerup, Stevns Klint.

Occurrence. Moderately common in the Cerithium Limestone Member at Stevns Klint. This species is also present in the contemporaneous ‘dead layer’ in Dania Quarry, Northern Jutland, as evidenced by material collected by K.I. Schnetler. Furthermore it seems to range down into the Maastrichtian Højerup Member, though better material may show this to represent a separate species.

Description. Protoconch obtusely conical, consisting of 2 ¾ smooth and convex whorls meeting at a marked angle. Transition to teleoconch sharp, marked by the appearance of sharp transverse ribs and finer spiral cords or threads, and by a change in spire angle.

Teleoconch rather compact biconic fusiform with distinct stepped outline and short canal. Whorls moderately low, twice as wide as high, with strongly developed shoulder and distinct subsutural spiral swelling and constriction at adapical suture. Shoulder ramp concave. Aperture subtriangular with distinct adapical channel and rather gradual transition to wide and short siphonal canal; siphonal canal with rounded distal termination. Callus rather narrow, on parietal region additionally very thin, allowing the underlying spiral ribs to appear as weak folds. Apertural lips and columella otherwise smooth.

Teleoconch sculpture dominated by around 15 to 18 short and sharp, opisthocline and slightly opisthocyrt transverse ribs; ribs highest at shoulder, tapering out towards sutures. Transverse ribs partly effaced at adapical whorl constriction, becoming stronger again on subsutural swelling. Spiral cords fine and close together, increasing in number with whorl size. Growth lines sigmoid, describing wide U-shaped sinus on abapical part of shoulder ramp.

Measurements. Largest complete specimen, MGUH 33283, 14.9 mm high and 6.2 mm wide, consisting of protoconch and four teleoconch whorls.

Remarks. Pseudotoma danica n. sp. differs from the contemporaneous Pseudotoma sp. figured by Kollmann & Peel (1983) from Greenland by a slightly more compact shell with a weaker shoulder and a more rounded distal termination of the siphonal canal. It is distinguished from the Danish Selandian P. steenstrupi ( von Koenen, 1885) by typically sharper and more numerous transverse ribs and a more gradual transition to the siphonal canal.

Figures

FIGURE 32. A. Ptychatractidae genus et sp. indet. Silicone cast of MGUH 33274. Width 1.8 mm. B–G. Orthosurcula s.l. cerithiorum (Ravn, 1902). B. Silicone cast of lectotype MGUH 123. Height 11.4 mm. Photograph by S. L. Jakobsen. C. Silicone cast of MGUH 33275. Height 4.8 mm. D. Silicone cast of MGUH 33276. Height 13.7 mm. E. Silicone cast of MGUH 33277. Width 6.4 mm. F. Silicone cast of MGUH 119, holotype of Pleurotoma steenstrupii Ravn, 1902. Height 23.6 mm. G. Silicone cast of MGUH 33278. Height 2.4 mm. H–K. Epalxis? rosenkrantzi n. sp. H–J. Silicone cast of holotype MGUH 33279. Widths 2.7, 2.8 and 2.8 mm respectively. K. Silicone cast of paratype MGUH 33280. Width 2.5 mm. L–N. Pseudocochlespira transversa n. sp. L–M. Silicone cast of holotype MGUH 33281. Widths 5.9 and 6.0 mm respectively. N. Silicone cast of paratype MGUH 33282. Width 8.2 mm. O–S. Pseudotoma danica n. sp. O–P. Silicone cast of holotype MGUH 33283. Width 5.7 mm. Q. Silicone cast of paratype MGUH 33284. Width 7.0 mm. R. Silicone cast of paratype MGUH 33285. Width 6.3 mm. S. Silicone cast of ØSM.10042-272-b. Width 5.8 mm. T–U. Mangeliid genus et sp. indet., Silicone cast of MGUH 33286. Widths 3.3 and 4.8 mm respectively.