Pelagiella sp. 1
publication ID |
https://doi.org/ 10.4202/app.2012.0004 |
persistent identifier |
https://treatment.plazi.org/id/03C3891D-1523-C263-FCBF-FA72CA86F930 |
treatment provided by |
Felipe |
scientific name |
Pelagiella sp. 1 |
status |
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Figs. 17 View Fig , 18 View Fig , 19A View Fig .
Material.—Nine calcium phosphatic internal and external moulds, including figured SMNH Mo 167679–167685 from sample 7/70 and six moulds from sample K1-3B. Uppermost Emyaksin Formation, Bol’shaya Kuonamka and Malaya Kuonamka rivers; Calodiscus -Erbiella Zone, lower Botoman Stage.
Description.—Very rapidly expanding shell consisting of up to ¾ whorl. Aperture wide, asymmetrical, with pinched and strongly drawn-out peripheral side ( Figs. 17A View Fig 3 View Fig , 19A View Fig 2 View Fig ). The peripheral surface of the whorl is rounded and distally extended, separated from the spiral and umbilical surfaces by an angle.The spiral surface of the whorl is depressed and concave, whereas the umbilical surface is convex ( Figs. 17A View Fig 1 View Fig , 19A View Fig 1 View Fig ). Ornamentation of the shell exterior consists of fine radial striations, 1–3 μm wide, and transversal, narrow ribs. Distance between ribs up to ~50 μm ( Fig. 18 View Fig ). The ornamentation of ribs fades out towards the periphery of the
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whorl ( Fig. 18B View Fig ). A sinusoidal course of ribbing follows the relief of the umbilical and upper spiral surfaces.
Remarks.—The fossils described here are generally most similar to Pelagiella madianensis ( Zhou and Xiao, 1984) illustrated in Gravestock et al. (2001: pl. 46), but the ornamentation of P. madianensis consists of granules arranged in spiral rows (Parkhaev in Gravestock et al. 2001). The ornamentation of Pelagiella sp. 1 herein consists of comarginal ribs similarly spaced as in the middle Cambrian Pelagiella sp. cf. Costipelagiella zazvorkai from the overlying Kuonamka Formation ( Kouchinsky et al. 2011), but they do not appear to extend to the periferal portion of the whorl. Pelagiella sp. 1 differ from Pelagiella sp. 2 described below in having a strongly extended peripheral part of the aperture and whorl, a more depressed spiral side and more rapidly expanding whorl. Unlike other species of Pelagiella , Pelagiella sp. 1 has a strongly extended peripheral part of the aperture.
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