Opalia, H.Adams & A.Adams, 1853

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 127-128

Opalia sp.

Figs 29 L–N

Material. MGUH 33234 and MGUH 33235, both external and internal moulds.

Occurrence. The lower Danian Cerithium Limestone Member at Stevns Klint.

Description. Protoconch high conical, approximately 0.4 mm high and 0.3 mm wide, consisting of around 2 ½ moderately convex whorls. Embryonic whorl small, smooth or granulate. Larval whorls 1 ½ to two in number, carrying around 30 opisthocline collabral threads per whorl.

Teleoconch moderately slender with highly convex whorls separated by very deep suture. Whorl width nearly twice as large as height. Transition to flattened base marked by basal carina. Base smooth but for weak and wide spiral furrows. No umbilicus present. Aperture rounded ovoid with weakly concave columella.

Teleoconch sculpture dominated by around 14 sharp-ridged transverse ribs per whorl; ribs crossed by five or six weaker spiral ribs or threads, the abapical four much stronger than adapical ones.

Measurements. Specimen MGUH 33234 is 3.6 mm high and 1.25 mm wide, consisting of protoconch and 5 ¾ teleoconch whorls.

Remarks. Opalia sp. differs from the early Palaeocene Cerithiscala sp. of Kollmann & Peel (1983) from Greenland by the higher number of spiral threads. Likewise it is easily distinguished from the middle Danian Opalia tricincta ( Ravn, 1933) from Denmark, by the finer sculpture, the more slender outline and the more convex whorls. It differs from the Selandian Opalia poulseni ( Ravn, 1939) from Denmark by the finer sculpture and broader outline, and from the Selandian Opalia hauniensis ( Ravn, 1939) , also from Denmark, by the stronger spiral sculpture.

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.