Amaea aliceae, Hansen, 2019

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 129-130

Amaea aliceae n. sp.

Figs 29 S–V

Diagnosis. Shell slender with generally strongly convex whorls and flattened base. Teleoconch carrying five to six well developed spiral ribs on early whorls and around 35 transverse ribs per whorl. Transverse ribs typically only slightly weaker than spiral ribs, but may fade out on later whorls.

Derivation of name. In honor of the late Alice Rasmussen from Faxe.

Type material. The holotype MGUH 33239 is a nearly complete external and internal mould lacking protoconch. Paratype MGUH 33240 is an external mould of apex from the lithified top of the Højerup Member at Holtug.

Additional material. Eight external and internal moulds without numbers are found in the old collections of the Natural History Museum of Denmark.

Type stratum and type locality. The lithified top of the upper Maastrichtian Højerup Member at Holtug, Stevns Klint .

Occurrence. Lithified top of the Maastrichtian Højerup Member, Tor Formation, at Rødvig, Mandehoved and Holtug Quarry, Stevns Klint.

Description. Shell very high and slender turriculate. Protoconch high conical, consisting of about three whorls. Embryonic whorl appearing smooth and slightly inflated. Larval whorls with dense pattern of around 45 to 50 fine opisthocline and forward concave collabral threads per whorl.

Teleoconch fairly thin-shelled; whorls strongly convex with impressed suture, width corresponding to between 2 and 2½ times the height. Transition to base moderately sharp, marked by slight angle, becoming more gradual on later whorls. Base flattened to weakly convex on early whorls, with moderately sharp transition to short but well developed canal; base becoming more convex on later whorls.Aperture subrectangular with short and concave columella terminating abapically in columellar fold. Columellar lip covered by thin callus. Siphonal canal deep.

Early teleoconch whorls covered by reticulate pattern of fine and sharply defined spiral ribs crossed by equally strong transverse ribs. Spiral ribs numbering five to six above abapical suture and one below. Transverse ribs slightly opisthocyrt, numbering around 35 per whorl or slightly below, terminating at abapical spiral rib. Whorl sculpture on larger specimens consisting of seven to eight fine but strong spiral ribs. Base smooth, while canal carries weak and low spiral ribs. Growth lines on whorls weakly opisthocyrt and opisthocline.

Measurements. Largest specimen consisting of four teleoconch whorls 9.05 mm high and 4.5 mm wide. Holotype specimen MGUH 33239 is more than 7.6 mm high (protoconch lacking) and 2.65 mm wide with 7 ¾ teleoconch whorls.

Remarks. A Danish middle Danian specimen strongly resembling Amaea aliceae n. sp. is illustrated by Damholt & Rasmussen (2005: p. 40) as Amaea elegans ( Ravn, 1902) . It is unclear whether they could represent the same taxon as the middle Danian specimen lacks the protoconch. Even so it is clear that neither belongs to A. elegans as evidenced by the presence of no more than around six spiral ribs, which are rather strongly developed, and by the smooth and less strongly delineated base. Amaea aliceae n. sp. seem to differ from the Danish middle Danian Acrilla sp. 1 sensu Lauridsen & Schnetler (2014) by the fine collabral threads on the protoconch and much denser sculpture of transverse teleoconch ribs.

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.