Thereitis, Le Renard, 1998

Hansen, Thomas, 2019, Gastropods from the Cretaceous-Palaeogene boundary in Denmark, Zootaxa 4654 (1), pp. 1-196 : 117

Thereitis sp.

Fig. 28E

Material. Specimen MGUH 33209 is an external mould of the protoconch and first five teleoconch whorls.

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

Description. Protoconch 0.7 mm high and 0.4 mm wide, multispiral, high conical with 5 ½ convex whorls separated by fairly deep sutures. First three whorls strongly expanding, following whorls of nearly equal width. First whorl smooth, the following covered by two peripheral to abapical spiral threads and up to 30 opisthocyrt and opisthocline collabral threads.

Teleoconch very slender, nearly parallel-sided, narrower than protoconch; whorls weakly, but distinctly convex, their height corresponding to their width. Teleoconch sculpture dominated by three to five spiral ribs, the three central ones strongest. Weakly developed and slightly prosocline transverse ribs are present between spiral ribs, giving the whorls a slightly reticulate sculpture.

Measurements. Specimen MGUH 33209 is 2.3 mm high and 0.4 mm wide, consisting of 10 whorls.

Remarks. The taxon differs from Thereitis cretacea n. sp. described above by the extremely slender spire with its narrow, but clearly convex teleoconch whorls carrying up to five spiral ribs. With only one available specimen so far it is unclear whether these differences are all true diagnostic characters or if some may reflect abnormal interspecific variation.

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.