Eumetula, Thiele, 1912

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 120-121

Eumetula sp.

Fig. 28R

Material. A single mould, MGUH 33218.

Occurrence. The taxon is known exclusively from the lithified top of the upper Maastrichtian Højerup Member of the Tor Formation at Rødvig, Stevns Klint.

Description. Protoconch 0.4 mm high and 0.35 mm wide, conical multispiral with approximately 3 ½ convex whorls. First 1 ½ (embryonic) whorls seemingly smooth, subsequent whorls covered by up to around 35 closely spaced and very fine opisthocyrt collabral threads per whorl. A keel or coarse spiral rib appears on first post-embryonic whorl, while a second is added on last protoconch whorl.

Teleoconch slender turriculate, with evenly increasing whorl width; whorls weakly convex, constricted at narrow adapical suture bordered by spiral ribs; whorl height corresponding to half or slightly more than half the width. Transition to smooth flat base sharp, marked by subperipheral carination. Base flattened, smooth. Aperture unknown.

Teleoconch sculpture dominated by coarse and weakly opisthocline transverse ribs, strongest centrally on whorl, interrupted adapically and at carination abapically, giving an impression of a more convex whorl; rib number increasing gradually with growth from around 14 on first teleoconch whorl. A more or less distinctly developed spiral rib and succeeding furrow occur adjacent to adapical suture. Interspaces between transverse ribs characterized by an additional five secondary and very weak spiral ribs.

Measurements. Specimen MGUH 33218 is 3.6 mm high and 0.9 mm wide, consisting of 3 ½ protoconch and eight teleoconch whorls.

Remarks. Eumetula sp. may be the oldest taxon assigned this genus so far, moving the generic range back to the Maastrichtian (see Gründel 1980). Eumetula sp. somewhat resembles the Belgian Cerithium regularicostatum Briart & Cornet, 1873 from the Danian, which was reassigned to Harrisianella Olsson, 1929 by Glibert (1973). Both taxa clearly do not belong to this genus as revised by Kowalke (2001: p. 260–261) and differ by much more convex whorls; the lack of an adapical subsutural spiral furrow and, at least with regard to the Danish taxon, by the densely sculptured protoconch whorls. The Danish taxon differs from Eumetula regularicostatum by the rather weakly convex teleoconch whorls and a more pronounced spiral rib demarcating the base. It is clearly distinguished from the Selandian Harrisianella subglabra Schnetler, 2001 from Denmark by the fewer and strongly sculptured protoconch whorls and by the more compact teleoconch whorls with their abapical spiral rib. The Selandian species does not belong within Harrisianella for the same reasons as for the species above and due to the high, multispiral protoconch.

Figures

FIGURE 28. A. Thereitis carlsbergi n. sp., Protoconch of paratype MGUH 33205.Width of protoconch 0.4 mm. B–D. Thereitis cretacea n. sp. B. Holotype protoconch MGUH 33206. Width 0.4 mm. C. Silicone cast of paratype MGUH 33207. Width 0.9 mm. D. Silicone cast of paratype MGUH 33208. Width 1.1 mm. E. Thereitis sp., Silicone cast of MGUH 33209. Width 0.4 mm. F–I. Cerithiella moltkianum (Ravn, 1902). F–H. Silicone cast of MGUH 33210. Width of teleoconch 4.6 mm. Height of protoconch 1.0 mm. I. Silicone cast of MGUH 33211.Width 9.2 mm. J–O. Cerithiella selandica n. sp. J–K. Silicone cast of holotype MGUH 33212. Teleoconch width 2.6 mm. Preserved protoconch width 0.5 mm. L–M. Silicone cast of paratype MGUH 33213. Height 31 mm. N. Paratype protoconch MGUH 33214. Width 0.7 mm. O. Silicone cast of paratype MGUH 33215. Width 2.6 mm. P–Q. Cerithiella sp. P. Silicone cast of MGUH 33216. Width 6.7 mm. Q. Silicone cast of MGUH 33217. Width 5.1 mm. R. Eumetula sp., Silicone cast of MGUH 33218. Width 0.9 mm. S. Trituba obliquecostulata (Kaunhowen, 1898). Silicone cast of MGUH 33219. Width 1.2 mm. T–V. Vatopsis heinbergi n. sp. T. Silicone cast of holotype MGUH 33220. Width 1.2 mm. U. Silicone cast of paratype MGUH 33221. Width 3.1 mm. V. Silicone cast of paratype MGUH 33222. Width 4.0 mm. W. Vatopsis sp., Silicone cast of MGUH 33223. Width 2.5 mm. X–Y. Ageria skeldervigensis n. sp. X. Silicone cast of paratype MGUH 33224. Height 4.1 mm. Y. Silicone cast of paratype MGUH 33225. Width 7.4 mm.