Buxtonia scabricula (Sowerby, 1814)

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

Buxtonia scabricula (Sowerby, 1814)

Figs. 11M, N , 12A–C .

1809 Conchyliolithus Anomites ( scabriculus ); Martin 1809: 8, pl. 34: 5.

1814 Productus scabriculus ; Sowerby 1814: pl. 69: 1.

1862 Productus scabriculus Sowerby, 1814 ; Davidson 1862 a: 169, pl. 42: 5–8. (cum syn.)

1905 Productus scabriculus Sowerby, 1814 var. costata ; Vaughan 1905: 293.

1951 Buxtonia scabricula (Sowerby, 1814) ; Muir-Wood 1951: fig. 358: 1a–e.

1952 Buxtonia scabricula (Sowerby, 1814) ; Sarycheva and Sokolskaya 1952: 96, pl. 114.

1960 Buxtonia scabricula (Sowerby, 1814) ; Muir-Wood and Cooper 1960: pl. 53: 10–11; pl. 74: 8–11.

1965 Buxtonia scabricula (Sowerby, 1814) ; Muir-Wood 1965: fig. 358: 1.

1991 Buxtonia scabricula (Sowerby, 1814) ; Brunton and Tilsley 1991: 291.

2000 Buxtonia scabricula (Sowerby, 1814) ; Brunton et al. 2000: fig. 338: 3a–c.

Material.—Seven articulated specimens: MPUM 11959

RCC 1B-13); MPUM 11960 ( RCC 35A-11a); MPUM 11961

WI1-14); MPUM 11962 (WI1-38); MPUM 11963 (WI1-40); MPUM 11964 (WI1-24, 34). One ventral valve: MPUM 11965

RCC 1-6). Two fragments: MPUM 11966 ( RCC 128-10a); MPUM 11967 (WI1-15b). 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 subrectangular outline. Cardinal margin wide, almost corresponding to the maximum width. Ears small, concave. Both valves geniculated. Corpus cavity deep. Anterior commissure rectimarginate. Ventral visceral disc convex. Geniculation angle 80°. Umbo straight, dorsally directed. Trail long, tubiform, convex. Shallow, broad sulcus starting 10.0 mm from the beak, widening anteriorly, becoming obsolete on trail. Dorsal valve slightly concave, with flat ears and low rounded fold starting near the cardinal margin, widening anteriorly. Geniculation angle 90°.

Ornamentation consists of low, rounded ribs, irregular in width and heigh, more or less continuous, undulating on the trail. Interspaces narrow posteriorly on visceral discs, becoming as wide as ribs anteriorly and on trail. Ribs increasing in number anteriorly by bifurcation on the ventral valve; commonly bifurcations occur immediately anterior to spine bases. They number eight per 10.0 mm, 20.0 mm from the umbo. Low, rounded rugae on the ventral valve; on ears and umbonal flanks, two per 5.0 mm length, with narrow interspaces, not extending around front of valve. Thinner rugae on dorsal ears, rarely extending on whole of disc; rugae intersect with the cardinal margin forming an angle of 45° near the umbo. Prostrate spines arranged in concentric rows on ventral rugae. Spines randomly distributed on ventral visceral disc, on ribs. Near the anterior commissure the ribs become obsolete and finer and at least three staggered rows of small rounded spine bases are developed. Dorsal valve bearing elongated to circular dimples, more frequent near geniculation; dimples concentrically arranged on rugae interspaces on the flanks, irregularly disposed on fold; four dimples per 5 mm 2 at geniculation. Spine bases on ribs. Micro-ornamentation of concentric growth lines on both valves.

Cardinal process long-shafted, bilobed, quadrifid, apparently dorsally reflexed. Median septum short (6.0 mm long), thin, with small antron posteriorly.

Remarks.—The specimens resemble in their morphology and ornamentation the lectotype of Buxtonia scabricula figured by Brunton et al. (2000), from the upper Visean of Derbyshire, and the specimens figured by Muir-Wood and Cooper (1960) from the Visean of Flintshire, Wales. They differ from B. scabriculoides Paeckelmann, 1931 , in being smaller, in lacking a clear reticulation on the ventral disc and in having spines arranged on all the valve, rather than being restricted posteriorly; from B. lichwini (Lisitzyn, 1909) from the upper Tournaisian of the Moscow Basin in being sulcate ( Sarycheva and Sokolskaya 1952).

Stratigraphic and geographic range.— Buxtonia scabricula is common in upper Visean–lower Serpukhovian rocks of Great Britain and Ireland ( Vaughan 1905; Muir-Wood and Cooper 1960; Brunton and Tilsley 1991; this study) and upper Visean rocks of Central Iran ( Ruttner et al. 1968).

Figures

Fig. 11. Productidae from the Brigantian (uppermost Visean) of Ricklow Quarry, near Monyash, Derbyshire, UK (localities RCC-, RCK-; Fig. 3). A–F. Antiquatonia insculpta (Muir-Wood, 1928). A. MPUM11938 (RCC1B-9) in anterior (A1) and lateral (A2) views. B. MPUM11939 (RCC3-15a) in antero-ventral view. C. MPUM11940 (RCC42-26) in antero-ventral view. D. MPUM11941 (RCC110-1b) in lateral view. E. MPUM11944 (RCC2-25) ventral valve in ventral view. F. MPUM11947 (RCC128-2) dorsal valve interior and external cast. G, H. Dictyoclostus pinguis (Muir-Wood, 1928). G. MPUM11950 (RCC54-11) ventral valve in ventral view. H. MPUM11951 (RCK15-63a) dorsal valve external cast. I–K. Pugilis cf. kilbridensis (Muir-Wood, 1928). I. MPUM11956 (RCC128-3) dorsal valve interior and external cast. J. MPUM11955 (RCC54-4) ventral valve in anterior (J1) and lateral (J2) views. K. MPUM11954 (RCC2-47) ventral valve in anterior view. L. Pugilis cf. scotica (Sowerby, 1814), MPUM11958 (RCC2-41) in lateral (L1), ventral (L2), and anterior (L3) views. M, N. Buxtonia scabricula (Sowerby, 1814). M. MPUM11959 (RCC1B-13) in ventral view. N. MPUM11960 (RCC35A-11a) in ventral view.

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.