Coniscala umbilica, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 126-127

Coniscala umbilica n. sp.

Figs 29 H–K

Diagnosis. Blade-like costae not strongly shouldered, closely spaced with up to around 22 per whorl; costae only slightly flexed at transition to basal carina. Umbilicus open, relatively wide.

Derivation of name. Refers to the relatively wide umbilicus characterizing this species.

Type material. The holotype MGUH 33232 was collected by A. Rosenkrantz 21 July 1943 . Paratype MGUH 33233 is from the upper part of the Tor Formation exposed just north of Holtug Quarry , and was collected by Claus Heinberg in 1995 . Paratype MGUH 33231 is from the Cerithium Limestone Member at Holtug Quarry , and was collected by A. Rosenkrantz in 1940.

Additional material. A specimen with informal sample number SR.781, and an uncatalogued specimen, both with part of shell preserved, derives from the lithified top of the Tor Formation; ØSM.10042-90-a–b, two specimens with informal sample numbers DN.21 and DN.49, and four specimens without number comes from the ‘dead layer’ in Dania Quarry, Northern Jutland, and from the Cerithium Limestone Member at Rødvig, Holtug Quarry and Højerup at Stevns Klint. ØSM.10042-236-a–b and five additional specimens with no numbers derive from the Korsnaeb Member at Stevns Klint and Dania.

Type stratum and type locality. Basal Korsnaeb Member, or more precisely from the Korsnaeb Member infilled Thalassinoides burrows in the Cerithium Limestone Member at Harvig, Stevns Klint.

Occurrence. Lithified top of the Maastrichtian Tor Formation at Holtug Quarry, Stevns Klint; the lower Danian Cerithium Limestone Member and contemporaneous ‘dead layer’ from Stevns Klint and Dania Quarry, respectively, and their Korsnaeb Member outfilled Thalassinoides burrows.

Description. Shell spire high turriculate with well rounded whorls only just meeting neighbouring whorls. Sutures deep. Base of whorl with flattened disc or carina surrounding deep and moderately wide umbilicus, umbilicus taking up approximately 15 % of whorl width. Aperture broadly ovoid with slightly developed varix; height corresponding to around 75 % of width. Shell surface covered by very fine and dense spiral lirae and between 15 and 22 blade-like costae per whorl; costae composed of multiple lamellae, flexed subsuturally and, to a lesser degree, at transition to basal carina and to umbilicus; costae distinct on carinal disc. Protoconch not known.

Measurements. Holotype specimen, MGUH 33232, more than 35.4 mm high and 19.6 mm wide.

Remarks. Coniscala umbilica n. sp. is easily distinguished from most other species of Coniscala by its high lamellar ribs, the open and relatively wide umbilicus and the distinct costae on the carinal disc. It is probably most similar to the Palaeocene Cavoscala crispn Gorbach, 1972 from the Crimea, Russia, from which it differs by the coarser and sparser transverse ribbing. More material of the Crimean taxon may perhaps show them to represent different phenotypes of the same species. Coniscala umbilica n. sp. resembles the slightly younger C. faxensis Ravn, 1933 from the middle Danian of Denmark, and C. johnstrupi ( Mørch, 1874) from the Selandian of Denmark, but differs by the high and blade-like costae, slightly weaker spiral lirae, the generally wider umbilicus and possibly by a less pronounced basal disc. It strongly resembles the Late Maastrichtian Scalaria contorta Kaunhowen, 1898 from Holland, which was later assigned to Confusiscala Boury, 1909 by Abdel-Gawad (1986), but according to P. v. Knippenberg from Holland (pers. comm. 2009) it lacks the wide umbilicus of the Danish taxon. Coniscala umbilica n. sp. resembles species of the contemporaneous North American genus Striaticostatum Sohl, 1963 , and here especially S. bexarense ( Stephenson, 1941) , but differs by the wider umbilicus, the less honeycombed and more blade-like costae and by the distinctly less backwardly turned costae on the basal carina (compare with Sohl 1964a). Striaticostatum should probably be regarded as a subgenus of Coniscala .

Figures

FIGURE 29. A–B. Ageria skeldervigensis n. sp., Silicone cast of holotype MGUH 33226. Width 3.8, 4.5 mm respectively. C–E. Ageria laxa n. sp. C–D. Silicone cast of holotype MGUH 33227. Width 4.6 mm for teleoconch, 0.3 mm for protoconch. E. Silicone cast of paratype MGUH 33228. Width 6.7 mm. F–G. Ageria sp. F. Silicone cast of seemingly mislaid specimen MGUH 33229. Width 3.7 mm. G. Silicone cast of MGUH 33230. Width 0.6 mm. H–K. Coniscala umbilica n. sp. H. Silicone cast of paratype MGUH 33231. Width 1.4 mm. I–J. Holotype MGUH 33232. Width 19.6 mm. K. Paratype MGUH 33233. Width 12.4 mm. L–N. Opalia sp. L–M. Silicone cast of MGUH 33234. Width 1.3 mm. N. Silicone cast of MGUH 33235. Width 0.5 mm. O–Q. Claviscala minor n. sp. O–P. Silicone cast of holotype MGUH 33236. Width of teleoconch 0.9 mm. Width of protoconch 0.4 mm. Q. Silicone cast of paratype MGUH 33237. Width 1.3 mm. R. Claviscala sp., Silicone cast of MGUH 33238. Width 1.4 mm. S–V. Amaea aliceae n. sp. S–U. Silicone cast and inner mould of holotype MGUH 33239. Width 2.7, 2.0 and 3.1 mm respectively. V. Silicone cast of paratype MGUH 33240. Width 1.7 mm. W. Amaea stevniensis n. sp., Silicone cast of holotype MGUH 33241. Width 1.0 mm. X. Amaea sp. A. Silicone cast of MGUH 33242. Width of teleoconch 1.1 mm.