Beloitoceras cf. sinuoseptatum ( Roemer, 1861 )

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 82-83

Beloitoceras cf. sinuoseptatum ( Roemer, 1861)

Figs 16G , 32C, 33

Material examined

ESTONIA • 2 specs; Vormsi Island, Hosholm shore ; Adila Formation , Pirgu Regional Stage; GIT 878- 231 , GIT 426-2 .

Description

The nearly complete specimen GIT 878-231 ( Fig. 32C ) is relatively strongly curved during early growth stages (corresponding to conch heights <ca 40 mm) and reaches a maximum conch height of 53 mm at the base of the mature body chamber. There, the conch width is ca 37 mm (CHI = 1.43), and the conch cross section is oval in shape with narrow dorsal and ventral margins. The body chamber is 35 mm long and at the aperture 48 mm high. In lateral view, the dorsal and ventral margin of the body chamber is slightly convex. The peristome appears to be straight and simple. The phragmocone height increases from 40 mm to 53 mm at a length of 55 mm (angle of expansion = 13°). Between conch heights of 21–40 mm the conch expands at an angle of 19°. The sutures form shallow lateral lobes.

In specimen GIT 426-2, which is a short fragment of a phragmocone with five chambers, the details of the siphuncle are well-preserved ( Fig. 16G ). The siphuncular segments are trapezoidal, with adnate areas at the adapical surfaces of the septa. The septal necks are cyrtochoanitic.

Remarks

The two specimens are slightly more curved and larger than the fragments assigned to B. sinuoseptatum but otherwise indistinguishable from the types and the material herein assigned to B. sinuoseptatum sensu stricto, in which a maximum conch height of ca 44 mm occurs (see above).

Figures

Fig. 16 (next page). Median sections of phragmocone of cephalopods of the Pirgu Regional Stage, Estonia. A–B. Ephippiorthoceras vormsiense sp. nov. A. Holotype (GIT 878-192), from Hosholm shore (tower), Vormsi Island. B. Specimen TUG 1745-28, from Vohilaid shore (E), Vohilaid Island. C–D. Danoceras piersalense (Teichert, 1930) comb. nov. C. Specimen TUG 80-510, from Piirsalu quarry. D. Specimen TUG 1745-296, from Pirgu River outcrop. E. Dowlingoceras kallholnense Frye, 1987, from GIT 878- 247, from Hosholm shore, Vormsi Island. F. Danoceras piersalense specimen GIT 840-271, from Hosholm shore, Vormsi Island. G. Beloitoceras cf. sinuoseptatum (Roemer, 1861), specimen GIT 426-2 from Hosholm shore, Vormsi Island. Scale bars = 5 mm in all figures, same scale in A–G.

Fig. 32. Oncoceratidae Hyatt, 1884 of the Vormsi–Pirgu regional stages, Estonia. A–B. Beloitoceras sinuososeptatum (Roemer, 1861). A. Specimen TUG 939-56, from Haapsalu holm, Pirgu Regional Stage, lateral view. B. Specimen TUG 1723-26, from Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage, lateral view. C. Beloitoceras cf. sinuososeptatum (Roemer, 1861), specimen GIT 878-231, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. D. Cyrtorizoceras sp. A., specimen GIT 878-260, from Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage, lateral view.E–F. Cyrtorizoceras hariense sp. nov., holotype GIT 878-71, from Saxby shore (N), Vormsi Island, Estonia, Vormsi Regional Stage. E. View of prosiphuncular side. F. Lateral view. Scale bar = 20 mm, same scale in all figures.