Buxtonia sp.

Carniti, Alessandro P., Porta, Giovanna Della, Banks, Vanessa J., Stephenson, Michael H. & Angiolini, Lucia, 2022, Brachiopod fauna from uppermost Visean (Mississippian) mud mounds in Derbyshire, UK, Acta Palaeontologica Polonica 67 (4), pp. 865-915 : 892-893

Buxtonia sp.

Fig. 12D–E .

Material.—Two ventral valves: MPUM11968 (RCC8-2a); MPUM11969 (WI1-2). One fragment: MPUM11970 (RCC1- 39). All from mud mound complex of Ricklow Quarry, Monyash, Derbyshire, UK, Monsal Dale Limestone Formation, Brigantian (RCC-, RCK-), and Wensley Dale, Matlock, Derbyshire, UK, Eyam Limestone Formation, upper Brigantian, upper Visean (WI1).

Description.—Medium-sized, concavo-convex shell with transversely subtriangular outline; cardinal margin wide, maximum width attained at shell mid-length. Ears large, flat. Anterior commissure rectimarginate to gently uniplicate. Ventral valve moderately convex, not geniculated. Shallow sulcus starting near the umbo.

Ornamentation consists of low, rounded, ribs with narrow interspaces posteriorly on visceral discs, becoming wide anteriorly. Ribs increase in number anteriorly by bifurcation. They number 10–12 per 10.0 mm, 12.0 mm from the umbo. Prostrate, dense (5–6 in 5 mm 2 at 16.0 mm from the umbo) spines on ribs, concentrically arranged on flanks, irregularly on visceral disc and trail. Ventral visceral disc covered by rugae, six per 10.0 mm length, more prominent on ears and umbonal flanks, increasing in number around front of valve by intercalation. Rugae intersect the cardinal margin forming a 40° angle with it.

Remarks.—The specimens differ from the ones assigned to Buxtonia scabricula from the same localities in their less enrolled ventral valve and finer ornamentation. The gentle convexity of their ventral valve and the absence of a proper geniculation make them different from most other species of Buxtonia and closer to those of Marginicinctus , but they lack the anterior development of a gutter which is distinctive for the latter.

Figures

Fig. 12. Productidae and Echinoconchidae from the Brigantian (uppermost Visean) of Ricklow Quarry, near Monyash (localities RCC-, RCK-; see Fig. 3) and Wensley Dale, near Matlock (locality WI1; Fig. 2), Derbyshire, UK. A–C. Buxtonia scabricula (Sowerby, 1814). A. MPUM11963 (WI-40) in ventral view. B. MPUM11962 (WI1-38) in ventral (B1), dorsal (B2), and lateral (B3) views. C. MPUM11961 (WI1-14) in ventral (C1), dorsal (C2), and posterior (C3) views. D, E. Buxtonia sp. D. MPUM11968 (RCC8-2a) ventral valve in lateral (D1) and ventral (D2) views. E. MPUM11969 (WI1-2) ventral valve in ventral view. F. Buxtoniini gen. et sp. indet., MPUM11971 (RCK15B-1a) dorsal valve external cast. G–K. Echinoconchus punctatus (Sowerby, 1822). G. MPUM11983 (RCC1B-18) dorsal valve external cast. H. MPUM11980 (RCC54-7) ventral valve in ventral view. I. MPUM11975 (RCK15-21) in ventral view. J. MPUM11974 (RCC72-1) in ventral view. K. MPUM11977 (WI1-28) in lateral (K1), ventral (K2), dorsal (K3), and anterior (K4) views.