Rhynchorthoceras beyrichii Remelé, 1882

Aubrechtová, Martina & Korn, Dieter, 2022, Taxonomy and ontogeny of the Lituitida (Cephalopoda) from Orthoceratite Limestone erratics (Middle Ordovician), European Journal of Taxonomy 799 (1), pp. 1-108 : 21-24

Rhynchorthoceras beyrichii Remelé, 1882

Fig. 14D , Tables 2–3

Rhynchorthoceras Beyrichii Remelé, 1882: 128 , pl. 5 fig. 3a–b.

Orthoceratites – Breyn 1732: 33, pl. 4 figs 1–3.

Ancistroceras Breynii – Remelé 1881: 194.

Rhynchorthoceras beyrichi – Foerste 1930: 277, pl. 42 fig. 2a–c. — Balashov 1962: pl. 7 fig. 3.

Diagnosis

Species of the genus Rhynchorthoceras with an expansion angle of 15–17°. Shell surface with pronounced lirae, straight in the apical part but faintly sinuous later in ontogeny. Distance of lirae increasing up to 1.5 mm during ontogeny; distance and thickness of lirae might be irregular. Siphuncle eccentric in position (after Remelé 1882).

Type material

Not available for study; Remelé (1882: pl. 5 fig. 3a–b) did not specify a type, but he mentioned and illustrated only one specimen from Szczecin (formerly Stettin; West Pomerania, Poland), found in Upper Grey Orthoceratite Limestone erratics in Pleistocene gravel (late Darriwilian, Middle Ordovician).

Material examined

POLAND • 1 spec.; Osselsk ; Ordovician; Henke 1901 Coll.; MB.C.11718 .

Description

Specimen MB.C.11718 ( Fig. 14D ) is a 50 mm long fragment of an orthoconic phragmocone; it is sectioned along the median plane (a thin section was also produced by a previous researcher). The conch expands with an expansion angle of 17°. The ornament consists of flat, asymmetric lirae (the steeper side facing the aperture), which form a shallow lateral sinus and a low dorsal projection. The shell wall is not preserved on the ventral side. During ontogeny, the siphuncle shifts slightly in position (from 0.40–0.45); it has a diameter of 0.15 of the whorl height. The connecting rings are slightly expanded in their first half. The chamber length is stable (CLR = 0.25–0.27).

Remarks

Rhynchorthoceras beyrichii is distinguished from the other species of the genus by the moderately high expansion angle (15°–17°) and an ornament with sinuous lirae. The lirae are much less sinuous and narrower than in the otherwise similar R. breynii (from Middle Ordovician erratics of northern Germany) and R. zaddachi ( Remelé, 1882) (from Darriwilian erratics of the Kaliningrad Region, Russia).

Rhynchorthoceras beyrichii is a rare species that is unequivocally known only from two specimens figured by Remelé (1882) and Foerste (1930); the latter specimen was available for study herein. Dzik (1984) figured a specimen of Rhynchorthoceras from Volkhovian (early Middle Ordovician) strata of Poland that he assigned to R. aff. beyrichi .

Geographic and stratigraphic occurrence

Poland (in erratics within Pleistocene gravels); Upper Grey Orthoceratite Limestone, late Lasnamägi Regional Stage (late Darriwilian, Middle Ordovician).

Figures

Fig. 14. Species of Rhynchorthoceras Remelé, 1882 from the Upper Red Orthoceratite Limestone. A. Rhynchorthoceras conicum (Hisinger, 1837), specimen MB.C.30503 (Neben & Krueger Coll.) from Niederfinow (Brandenburg); lateral view. B. Rhynchorthoceras conicum (Hisinger, 1837), specimen MB.C.11719.1 (Otto Coll.) from an unknown locality; dorsal? view. C. Rhynchorthoceras conicum (Hisinger, 1837), specimen MB.C.30508 from Dewitz Castle, Dobra (former Dewitzburg bei Daber; West Pomerania, Poland); lateral? view. D. Rhynchorthoceras beyrichii Remelé, 1882, specimen MB.C.11718 (Henke 1901 Coll.) from Osselsk (Poland); previously figured by Foerste (1930: pl. 42 fig. 2); lateral view and polished median section. Scale bar units = 1 mm.