Obtusoconus cf. honorabilis (Qian, Chen, and Chen, 1979 )

Kouchinsky, Artem, Bengtson, Stefan, Landing, Ed, Steiner, Michael, Vendrasco, Michael & Ziegler, Karen, 2017, Terreneuvian stratigraphy and faunas from the Anabar Uplift, Siberia, Acta Palaeontologica Polonica 62 (2), pp. 311-440 : 339

Obtusoconus cf. honorabilis (Qian, Chen, and Chen, 1979)

Fig. 13D, E, J .

Material.—Three phosphatic internal moulds, SMNH Mo181974, 181975, and 181980, from K1a/67 and K8 (section 2, Fig. 1), Kugda-Yuryakh Formation, western Anabar Uplift. Correlated with the lower part of Cambrian Stage 2.

Description.—Bilaterally symmetrical, laterally compressed tall shell. Smaller shells nearly orthoconic ( Fig. 13J 1), with a slightly laterally deflected apex. Shell bent gently during later growth ( Fig. 13D 1, E 1). Aperture straight in side view, oval in plan view, with length/width ratio of ca. 2. The inner shell surface (as replicated by the internal moulds) has broad transverse folds.

Remarks.— Obtusoconus honorabilis (Qian et al. 1979) was first described from the Meishucunian Stage, Huanshandong Member of the Dengying Formation, Yichang County of the Hubei Province, South China. The fossils also similar to those assigned to Anuliconus Parkhaev in Gravestock et al., 2001, but the uncertainty in taxonomic assignment of these specimens is due to the absence of a protoconch on the available internal moulds. In contrast with Anuliconus , the protoconch in Obtusoconus is displaced and inclined opposite to the curvature of the conch. The protoconch is evidently much smaller than the globular, large protoconch in Obtusoconus rostriptuetus (Qian, 1978) . A generally similar form from Spain, O. reduncus (see Gubanov et al. 2004a) has a larger protoconch and is apparently more laterally compressed.

Figures

Fig. 13. Mollusc Obtusoconus Yu, 1979, internal moulds, from early Cambrian Emyaksin (A, C, F, I) and Kugda-Yuryakh (B, D, E, G, H, J) formations, Anabar Uplift, Siberian Platform, Russia; samples 5a/34.75 (A, C) and 5a/34.5 (F, I), section 96-5a, K2/60 (B, G) and K8 (D, E), section 3; K1a/67 (J), section 2; and M424/10 (H), section M424. A, C. Obtusoconus cf. mirabilis Vasil’eva, 1990, SMNH Mo181971 and 181973, respectively. B, G–I. Obtusoconus sp., SMNH Mo181972 (B), 181977–181979 (G–I, respectively). D, E, J. Obtusoconus cf. honorabilis (Qian, Chen et Chen, 1979), SMNH Mo181974 (D), SMNH Mo181975 (E), and SMNH Mo181980 (J), respectively. F. Obtusoconus vostokovae (Vasil’eva, 1990), SMNH Mo181976. A1–H1, I, J1, lateral; A2–H2, apical views; J2, view from right side as oriented in J1. Scale bar 1 mm.