Mellopegma uslonicum Parkhaev, 2004

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 : 435-436

Mellopegma uslonicum Parkhaev, 2004

Fig. 14 .

Material.—Seven calcium phosphatic internal moulds, including three SMNH Mo 160410, 167612, and 167671 from sample 7/70 and one internal mould SMNH Mo 167672 from sample B-247 (collected by Larisa G. Voronova and found in the collection of Vladimir V. Missarzhevsky). Uppermost Emyaksin Formation, Bol’shaya Kuonamka River; Calodiscus -Erbiella Zone, lower Botoman Stage.

Remarks.—Cyrtoconic, laterally highly compressed shell. The apex projects within the apertural margin. The aperture is elongated oval in outline (length/width ratio 3.0–3.7) and has a slight lateral flaring and subapical train. The surface of the internal mould bears faint concentric folds and is covered with evenly spaced blunt tubercles ( Fig. 14D ). The fossil is discussed as “Unnamed form 3” by Kouchinsky (2000a: fig. 5M–O). For discussion and comparison with other species see Vendrasco et al. (2011b: 18).

Stratigraphic and geographic range.—Lower Botoman Stage, Siberian Platform ( Vendrasco et al. 2011b and herein) and Eastern Transbaikalia ( Parkhaev 2004).

Figures

Fig. 14. Helcionellid mollusc Mellopegma uslonicum Parkhaev, 2004 internal moulds from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River, Anabar Uplift, Siberia; sample B-247 (A), sample 7/70 (B–D). A. SMNH Mo 167672; lateral (A1), sub-apical (A2), and upper (A3) views. B. SMNH Mo 167671; sub-apical (B1), lateral (B2), and upper (B3) views. C. SMNH Mo 160410; lateral (C1), upper (C2), and sub-apical (C3) views. D. SMNH Mo 167612; lateral view. Scale bar 600 μm, except D, 300 μm.