Bemella jacutica (Missarzhevsky, 1966)

Kouchinsky, Artem, Alexander, Ruaridh, Bengtson, Stefan, Bowyer, Fred, Clausen, Sébastien, Holmer, Lars E., Kolesnikov, Kirill A., Korovnikov, Igor V., Pavlov, Vladimir, Skovsted, Christian B., Ushatinskaya, Galina, Wood, Rachel & Zhuravlev, Andrey Y., 2022, Early-middle Cambrian stratigraphy and faunas from northern Siberia, Acta Palaeontologica Polonica 67 (2), pp. 341-464 : 377

Bemella jacutica (Missarzhevsky in Rozanov and Missarzhevsky, 1966)

Fig. 24M, N .

Material.—Several calcium phosphatic internal moulds, including figured SMNH Mo194703–194704, from sample 11/16.1, basal Erkeket Formation, Khorbusuonka River, Siberia, Russia. Dokidocyathus regularis Zone, Tommotian stage (correlated with the upper part of Cambrian Stage 2).

Remarks.—Smooth or having broad concentric folds internal moulds of rapidly expanding shells coiled less than 1/2 revolution, with broad oval aperture and rounded blunt initial part (see Kouchinsky et al. 2015a). Other low cyrtoconic forms from samples 11/2B and 11/16.1 represented by internal moulds, SMNH Mo194715 and Mo194716, with broad apertures and transversal ribs cannot be undoubtedly defined herein. They are referred to as Helcionellidae indet. ( Fig. 24J, K ).

Stratigraphic and geographic range. —Cambrian Stage 2, Siberian Platform.

Genus Obtusoconus Yu, 1979

Type species: Obtusoconus paucicostatus Yu, 1979 ; middle Meishucunian stage ( upper Fortunian –lower part of Cambrian Stage 2); Yichang County, western Hubei Province, South China .

Figures

Fig. 24. Molluscs from the lower Cambrian Erkeket Formation, Khorbusuonka River (A–F, J–N) and Sekten Formation, lower reaches of the Lena River (G–I), Siberia, Russia; samples 11/2B (E, F, J), 11/16.1 (K, M, N), 19/12.75 (A), 19/11.75 (B), 20/1B (L, O, P), 20/6B (C, D), and 22/50 (G–I). A, B. Davidonia anabarica (Parkhaev, 2005), internal moulds, SMNH Mo194701 and 194702, respectively. C. Mellopegma sp., internal mould, SMNH Mo194713. D. Stenotheca cf. drepanoida (He and Pei in He et al., 1984), silicified shell, SMNH Mo194714. D1, lateral view; D2, oblique apertural view. →