Striatocycloceras hosholmense Kröger 2025

Striatocycloceras cf. hosholmense Figs 11F, 13C Material examined ESTONIA • 3 specs; Vormsi Island, Hosholm shore; Adila Formation, Pirgu Regional Stage; TUG 899- 81, TUG 939-20, TUG 1745-233. Description Specimen TUG 939-20 is a fragment of a phragmocone, 38 mm long, with diameter 23–27 mm (apical angle 8.5°), and four chambers and annulations (Fig. 13C). The characters of the outer shell are not preserved. The annulations are directly transverse with deep troughs and sharply accentuated crests. The sutures are parallel to and positioned in the troughs of the annulations. The siphuncle is nearly centrally positioned and slightly expanded within the chambers. It is ca 2.5 mm wide at position of the septal foramen and 3.5 mm wide at mid-way between septa. The septal necks are orthochoanitic, 1.3 mm long (Fig. 11F). No cameral deposits are developed. Two additional specimens are in the Estonian collections which are similar in having a sharply crested annulations, ca three annulations per distance equal to the corresponding conch diameter and an apical angle of ca 10°. Remarks The specimens described as Striatocycloceras cf. hosholmense are in all aspect similar to Striatocycloceras hosholmense sp. nov. expect in having a distinctly larger apical angle at comparable conch diameters. However, none of the specimens has its outer shell preserved, making a comparison somewhat questionable. More material is needed to establish this group of specimens as a distinct species. Notably, a similar pair of species A. anellus and A. paquettense with low and high apical angles are known from Katian strata of North America (Foerste 1932: 104). This could indicate the presence of sexual dimorphism in this genus.