Conotheca circumflexa Missarzhevsky

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 : 445

Conotheca circumflexa Missarzhevsky in Rozanov et al., 1969

Fig. 27F .

Material.—One phosphatised conch, SMNH X 4629, from sample 7/55; Emyaksin Formation, Bol’shaya Kuonamka Riv- er; correlated with the Judomia Zone , upper Atdabanian Stage.

Description.—Conch helically curved about a half revolution clockwise towards the direction of growth. The aperture is straight and rounded, slightly oval. The surface of conch is covered with straight, faint, transverse lines. The apical angle is ca. 20°. Wall microstructure is similar to that of other hyoliths (see also Kouchinsky et al. 2009: fig. 45).

Stratigraphic and geographic range.—Lower Cambrian, Atdabanian Stage, Siberian Platform.

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. →