Nybyoceras bekkeri Troedsson, 1926

Figs 7A, 8A–B

Actinoceras (Nybyocera s) bekkeri Troedsson, 1926: 106–107, pl. 63 figs 1–3.

Actinoceras bigsbyi Bronn aff. – Eichwald 1860: 1253–1255 (partim).

Nybyoceras bekkeri – Teichert 1930: 287–288, pl. 6 figs 7–8, pl. 7 fig. 19; 1933: 130, 149, 176; 1964a: K208, fig. 2a–c. ― Foerste & Teichert 1930: 277, 279. ― Strand 1934: 62. ― Shimizu & Obata 1936: 119. ― Balashov 1953a: 210 (faunal list only). ― Teichert & Glenister 1953: 17–18. ― Stumbur 1956: 176. ― Flower 1957: 24. ― Sweet 1958: 48. ― Balashov & Zhuravlyeva 1962: 218, fig. 16, pl. 1 fig. 12. ― Dzik 1984: 149, text-fig. 57.17. ― Lehmann 1987: 193–194, pl. 3 figs 28–29.

Nybyoceras bekkei (sic) – Barskov 1972: 81.

Diagnosis

Nybyoceras with eccentric position of the siphuncle (RSP = 0.25), and with widely expanded siphuncular segments (SCR ca 2–2.5); incipient annuli grow in apical direction on the adoral surface of the septa; fully developed annuli are asymmetrically developed in longitudinal direction and are heavier on the ventral side. (Compiled from Teichert 1930.)

Material examined

ESTONIA • 1 spec.; Vormsi Island, Saxby shore; Kõrgessaare Formation, Vormsi Regional Stage; GIT 939-47 • 1 spec.; Vormsi Island, Saxby shore (N); Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1129 • 1 spec.; Saaremõisa (Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; TUG 1745-227 • 1 spec.; Sutlepa quarry; Kõrgessaare Formation, Vormsi Regional Stage; TUG 47-870 • 1 spec.; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1107 • 1 spec.; Kasari, Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-1120. (see also supplementary data 1) .

Type locality and horizon

Niibi, Estonia; Adila Formation, Pirgu Regional Stage.

Description

Specimen GIT 426-1107 (Fig. 8A) is a fragment of a phragmocone with a conch diameter of 66 mm, with a chamber length of 12 mm (RCL = 0.18) and a siphuncle, which is strongly expanded 24 mm in diameter (SCR = 2). The septal foramen is 7 mm wide. The connecting ring forms ventrally a wide (9 mm wide) area of adnation on the adoral surface of the septum and dorsally only a narrow (ca 3 mm wide) area of adnation on the adapical face of the septum. The septal necks are short and adnate. Incipient annuli grew in adapical direction and are more strongly developed on the ventral side of the conch.

Specimen GIT 426-1120 (Figs 7A, 8B) is a fragment of a phragmocone 125 mm long, and increasing in conch diameter 43–58 mm (angle of expansion= 7°), a circular conch cross section, a septal spacing with RCL of 0.2, and an RSP of 0.32. Specimen GIT 426-1129 is a fragment of a phragmocone 72 mm long, and increasing in conch diameter from 54–62 mm (angle of expansion= 6°), a septal spacing with RCL of 0.2, and an RSP of 0.23. Specimen TUG 1745-227 is a fragment of a phragmocone 78 mm long, and increasing in conch diameter 50–60 mm (angle of expansion= 7°), a septal spacing with RCL of 0.3, and an RSP of 0.33.

Remarks

The specimens assigned herein to N. bekkeri have an angle of expansion of 6–7°. This differs from the specimen figured in Teichert (1930: pl. 7 fig. 19), which expands with 12°. Because the angle of expansion is not known from the type-material (see Troedsson 1926), the diagnostic value of this character cannot be evaluated until more material from this species is known.