Triplicatella, Conway Morris, 1990

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 : 453

Triplicatella cf. T. peltata Skovsted, Peel, and Atkins, 2004

Fig. 29D .

Material.—Single phosphatised operculum, SMNH X 4649, from sample 7/70; uppermost Emyaksin Formation, Bol’shaya Kuonamka River; Calodiscus -Erbiella Zone, lower Botoman Stage.

Description.—The operculum has a rounded trapezoidal shape in plan view, ca. 1 mm wide, convex, with a single and prominent fold on the dorsal margin. In lateral view, the crest of the fold reaches the apex ( Fig. 29D 4 ). The internal surface is smooth, with a deep median depression in the sub-central part. Two short and rounded converging lateral ridges are situated near the dorsal margin.

Remarks.—Specimens of Triplicatella peltata Skovsted, Peel, and Atkins, 2004 from the Cambrian Stage 4 of Laurentia are similar in outline, number of folds and structure of the inner surface, although the dorsal fold is broader and more prominent than in the fossil herein.

Figures

Fig. 29. Hyolith opercula Triplicatella spp. from lower Cambrian Emyaksin Formation, Malaya Kuonamka River and Bol’shaya Kuonamka River, Anabar Uplift, Siberia. A, B. Triplicatella papilio sp. nov. A. SMNH X 4646, holotype, sample K1-3B; dorsal (A1), lateral (A2, A4), inner (A3), and ventral A5, note flattened rounded polygons at the base of the dorsal folds) views. B. SMNH X 4647, paratype, sample 7/70; dorsal (B1) and inner (B2) views. C. Triplicatella sinuosa Skovsted, Peel, and Atkins, 2004; SMNH X 4648, sample B-247; outer (C1), oblique ventral (C2), lateral (C3), and dorsal (C4) views. D. Triplicatella cf. T. peltata Skovsted, Peel, and Atkins, 2004; SMNH X 4649, sample 7/70; dorsal (D1), inner (D2), oblique inner (D3), and lateral D4) views. Scale bar 600 μm, except A1, A5, 300 μm.

Fig. 4. Helcionellid mollusc Bemella? sp. internal moulds from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River,Anabar Uplift, Siberia; sample 7/36.7. A. SMNH Mo 167650; lateral (A1), apertural (A2), and sub-apical (A3) views. B. SMNH Mo 167651; lateral (B1) and upper (B2) views. C. SMNH Mo 167652; apertural (C1), lateral (C2), and sub-apical (C3) views. D. SMNH Mo 167653; D1, close-up of apertural margin in D3; upper (D2) and lateral (D3) views. Scale bar 1200 μm, except D1, 300 μm.