Obtusoconus cf. mirabilis Vasiljeva, 1990

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

Obtusoconus cf. mirabilis Vasiljeva, 1990

Fig. 24E, F .

Material.—Two calcium phosphatic internal moulds, SMNH Mo194705 and 194706, from samples 11/2B and a single mould from sample 11/16.5, basal Erkeket Formation, Khorbusuonka River, Siberia, Russia. Dokidocyathus regularis Zone, Tommotian stage (correlated with the upper part of Cambrian Stage 2).

Remarks.—Bilaterally symmetrical, rapidly expanding orthoconic laterally compressed shells with oval aperture (length/width ratio ca. 2) and a globular, slightly laterally displaced protoconch. The inner shell surface (as replicated on the internal moulds) with regularly spaced broad transverse folds. Specimens described as Obtusoconus cf. mirabilis Vasiljeva, 1990 , by Kouchinsky et al. (2017: fig. 13A, C) have irregularly spaced transverse folds. See Kouchinsky et al. (2017) for comparison with other species of Obtusoconus .

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. →