Fusella sp.
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publication ID |
https://doi.org/ 10.4202/app.00972.2022 |
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persistent identifier |
https://treatment.plazi.org/id/41708783-FFF0-FF9D-8C7E-C96CFE92F80C |
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treatment provided by |
Felipe |
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scientific name |
Fusella sp. |
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Fig. 14M View Fig .
Material.—One ventral valve: MPUM12037 (RCC128-5) from mud mound complex of Ricklow Quarry, Monyash, Derbyshire, UK, Monsal Dale Limestone Formation, Brigantian, upper Visean.
Description.—Small, strongly transverse shell. Maximum width at the cardinal margin. Cardinal angles strongly acute; cardinal extremities evolving from mucronate to subrounded during growth. Ventral interarea wider, apsacline. Sulcus starting as a furrow from the umbo, becoming larger and deeper towards the anterior commissure.
Costate: a median costa occurs in the sulcus, starting 6.5 mm from the umbo. Flanks covered by simple, subrounded costae with narrow interspaces, extending from the umbo, becoming lower and indistinct laterally. Four costae per 5.0 mm, 5.0 mm from the umbo. The two sulcus-bounding costae are only slightly wider than the other ones. Strong and irregular concentric ornamentation given by imbricated lamellae.
Remarks.—The specimen is tentatively assigned to Fusella as it shows a median sulcal costa and lacks disproportionately larger sulcus-bounding costae. It differs from F. fusiformis (re-figured by Waterhouse 1970: fig. 1a–f), which is ornamented by numerous weak costae, and from F. rhomboidea ( Brunton and Rissoné 1976: pl. 11: 6–7; Brunton 1984: figs. 120–127), which lacks a median sulcal costa. The specimen has some similarities with Spirifer triangularis Sowerby, 1827 , from the Visean of England and Belgium, assigned to Fusella by Muir-Wood (1951). However, F. triangularis is characterised by having a strongly transverse ventribiconvex shell with an elevated and narrow dorsal fold, extending anteriorly. The specimen is left under open nomenclature on the basis of its poor preservation.
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