Hyolithida, Sysoev, 1957

Kouchinsky, Artem, Bengtson, Stefan, Clausen, Sébastien & Vendrasco, Michael J., 2015, An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia, Acta Palaeontologica Polonica 60 (2), pp. 421-512 : 456

Hyolithida sp. indet. 2

Fig. 27K .

Material.—Two pyritised conchs, including SMNH X 4659, from sample 1/9. The last specimen represents an almost complete but unsatisfactorily preserved conch with operculum attached to the aperture. Carbonate concretions of the basal Kuonamka Formation, Malaya Kuonamka River; Bergeroniellus expansus Zone , upper Botoman Stage.

Description.—The conch is gently curved dorso-ventrally at its initial part and has a convex, arched dorsal surface with 8–9 low longitudinal folds and a flattened ventral surface. In dorsal view, the apical angle is ca. 15°. The juvenile conch is elongated, tapered, slightly curved dorsally with respect to the main conch.

Figures

Fig. 27. Hyolith conchs from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River and basal Kuonamka Formation, Malaya Kuonamka River, Anabar Uplift, Siberia. A–E, H. Conotheca cf. C. mammilata Missarzhevsky in Rozanov et al., 1969. A. SMNH X 4623, sample 7/29; longitudinal view on presumably dorsal side. B. SMNH X 4621, sample 7/27.5; longitudinal view on presumably dorsal side. C. SMNH X 4622, sample 7/27.5; longitudinal view. D. SMNH X 4663, sample 7/30; D1, transversal view from the apertural end; D2, longitudinal view. E. SMNH X 4620, sample 3/65; lateral (E1) and dorsal (E2) views. H. SMNH X 4624, sample 7/31.5; longitudinal view. F. Conotheca circumflexa Missarzhevsky in Rozanov et al., 1969, SMNH X 4629; F1, oblique longitudinal view showing transversal section; F2, longitudinal view. G, J. Linevitus? minutus Missarzhevsky in Rozanov and Missarzhevsky, 1966. G. SMNH X 4657, sample 7/31.5; lateral (G1), dorsal (G2), and apertural (G3) views. J. SMNH X 4658, sample 7/70; ventral side with growth increments. →