Gorbyoceras sp. A

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 : 45

Gorbyoceras sp. A

Fig. 12N

Material examined

ESTONIA • 1 spec.; Kohila quarry ; Kõrgessaare Formation , Vormsi Regional Stage; TUG 42-417 .

Description

The specimen is a ca 75 mm long fragment of a curved body chamber with external sculpture partly preserved. The original diameter was larger than 35 mm. The fragment is annulated with ca 4–5 regularly spaced annulations per distance equal to the corresponding conch diameter. The annulations are relatively shallow. Additionally, the conch is ornamented with numerous fine longitudinal lirae and subordinate transverse growth lines, producing a reticulate pattern. The longitudinal and transverse lirae are ca 1 mm distant.

Remarks

The ornamentation of this fragment is similar to other species of Gorbyoceras . Its curved, relatively large body chamber (conch diameter> 35 mm) is similar to G. textumaraneum , from which it differs by its fine reticulate ornamentation. The fragmentary preservation of this specimen does not permit a species level determination.

Figures

Fig. 12 (next page). Orthocerida Kuhn, 1940 and Pseudorthocerida Flower & Caster, 1935 of the Vormsi– Pirgu regional stages, Estonia. A. Isorthoceras sp. A, specimen GIT 878-128, Sutlema quarry, Vormsi Regional Stage. B. Pleurorthoceras sp., specimen GIT 878-154, from Saxby shore, Vormsi Island, Vormsi Regional Stage. C. Gorbyoceras clathratoannulatum (Roemer, 1861) comb. nov., specimen GIT 878-305, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. D–E. Gorbyoceras textumaraneum (Roemer, 1861). D. Specimen GIT 878-143 from Vohilaid shore, Vohilaid Island, Pirgu Regional Stage. E. GIT 878-223, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. F. Isorthoceras sp. C, specimen GIT 878-49, Saxby shore, Vormsi Island, Vormsi Regional Stage. G. Isorthoceras sp. B, specimen GIT 878-116, from Moe trench, Vormsi Regional Stage. H. Gorbyoceras clathratoannulatum, specimen GIT 840-265, from Hosholm shore (tower), Vormsi Island, Pirgu Regional Stage. I. Isorthoceras sp. D, specimen GIT 878-114, Moe trench, Vormsi Regional Stage. J. Gorbyoceras stumburi (Kröger, 2013), specimen TUG 939-30, from Harilaid, Pirgu Regional Stage. K. Palaeodawsonocerina? sp., specimen TUG 939-78, from Hosholm shore, Vormsi Island, Pirgu Regional Stage. L–M. Gorbyoceras textumaraneum. L. Specimen TUG 1745-193, from Mõnuste quarry, Vormsi Regional Stage, lateral view. M. Specimen GIT 878-306, from Vohilaid shore (E), Vohilaid Island, Pirgu Regional Stage. N. Gorbyoceras sp. A, specimen TUG 42-417, from Kohila, Vormsi Regional Stage, lateral view. Scale bars = 10 mm in all figures. Same scale in A–B, F–G, I, N, and in C–E, H, J, L.