Pseudocochlespira transversa, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 150-151

Pseudocochlespira transversa n. sp.

Figs 32 L–N

Diagnosis. Protoconch low conical with 3 ½ convex smooth whorls, followed by a sculptured whorl carrying around 18 weak but sharp transverse ribs. Teleoconch with sharply developed carina, coarse spiral threads or cords and sharp transverse ribs.

Derivation of name. Refers to the generally well developed and sharp transverse ribs characterizing this species.

Type material. The holotype MGUH 33281 is a nearly complete part and counterpart of an external mould collected by A. Rosenkrantz in August 1924 . Paratype MGUH 33282 is an external mould from the same stratum and locality as the holotype.

Additional material. 12 external and internal moulds of the teleoconch are found in the uncatalogued old collections of the Natural History Museum of Denmark.

Type stratum and type locality. The Cerithium Limestone Member from just south of the Stevns Fyr at Stevns Klint.

Occurrence. Rare in the Cerithium Limestone Member , where it has been found at Skeldervig, Harvig, Højerup and just south of Stevns Fyr at Stevns Klint. A specimen from the contemporaneous ‘dead layer’ in Dania Quarry, Northern Jutland, has been examined in the collections of K.I. Schnetler.

Description. Protoconch moderately low, conical, multispiral, consisting of convex whorls separated by deep suture. Initial 3 ½ whorls smooth, succeeded by weakly carinated whorl with approximately 18 weak, but sharp, slightly opisthocline and distinctly opisthocyrt transverse ribs. Spiral cords weak but present.Apex of U-shaped and widely open growth line sinus and corresponding trajectory of transverse ribs located adapically of carina. Transition to teleoconch rather gradual. Embryonic smooth part of protoconch 1.2 mm high and 1.5 mm wide.

Teleoconch strongly elongate pagodiform in outline. Whorls relatively low, their height corresponding to 2/5 their width; whorls characterized by strongly developed median and flange-like peripheral carina, serration turned outwards to slightly adapically. Carina adapically bordered by an angularly concave shoulder slope with a nearly horizontal outer part and a slightly narrower inner part parallel to the axis. Aperture moderately wide and long, tapering evenly towards poorly differentiated narrow siphonal canal; combined height corresponding to 3/5 the shell height. Columella straight and smooth, with very weak central columellar plait. Outer lip apparently smooth.

Teleoconch sculpture consisting of sharp opisthocline and opisthocyrt transverse ribs and finer spiral cords. Transverse ribs rather weak, thread-like on shoulder slope to sometimes completely effaced, becoming stronger around whorl periphery, forming toothed carinal margin. Transverse ribs fade out on adapical part of base. Spiral cords or threads mostly present on base and canal, where they form a more or less dense surface sculpture. Generally three spiral threads are seen on abapical part of early spire whorls, increasing on later whorls. The shoulder slope is generally free of spiral sculpture, but may carry a single lamellar spiral rib just inside carina. Growth line sinus wide, U-shaped and shallow; its apex located at transition between inner and outer slope area.

Measurements. Holotype MGUH 33281 is approximately 12.7 mm high and 6.0 mm wide, consisting of around 6 ½ whorls, protoconch included.

Remarks. Pseudocochlespira transversa n. sp. differs from the Selandian P. boeggildi ( Ravn, 1939) from Denmark by a more pronounced carina and the obtuse protoconch with its deeper suture. It strongly resembles the Selandian P. koeneni ( Arkhanguelsky, 1904) from Denmark and Russia, but differs from it by the moderately developed spiral sculpture and by the less opisthocline and carinated nature of the transverse ribs on the last protoconch whorl. It differs from the Selandian P. rosenkrantzi Schnetler, 2001 from Denmark by the more obtuse outline of the protoconch and the sharp transverse ribs and stronger spiral cords on the teleoconch whorls. The growth lines are furthermore less oblique.

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.