Sowerbyella sinensis Wang

F. Nikitin, Igor, E. Popov, Leonid & G. Bassett, Michael, 2003, Late Ordovician brachiopods from the Selety river basin, north Central Kazakhstan, Acta Palaeontologica Polonica 48 (1), pp. 39-54 : 46-47

Sowerbyella sinensis Wang in Wang and Jin, 1964

Fig. 4C–H; Tables 5, 6.

Sowerbyella sinensis Wang in Wang and Jin, 1964: 46, pl. 13: 9–11.

Sowerbyella (Sowerbyella) sinensis Wang ; Xu 1996: 554, pl.2: 5–13, pl. 4: 8.

Sowerbyella (Sowerbyella) sinensis Wang ; Zhan and Cocks 1998: 40, pl. 5: 8–13.

Material.—More then 200 dorsal and ventral valves.

Description.—Shell concavoconvex, outline semioval, about 65% as long as wide and about 145% as thick as long. Cardinal extremities slightly acute to near right angled.Ante − rior margin broadly and evenly rounded, commissure rectimarginate.Ventral valve moderately and evenly convex in lateral profile, slightly carinate posteriorly in some specimens.Ventral interarea low, apsacline with a convex, apical pseudodeltidium.Dorsal valve gently and evenly concave, about 60% as long as wide.Dorsal interarea linear, anacline with discrete chilidial plates united apically.Radial ornament finely and unequally parvicostellate, with accentuated costellae of three generations separated by 2 to 3 parvicostellae in the interspaces and with up to 14 to 16 costellae per 3 mm at the anterior margin of mature specimens.

Ventral valve interior with teeth supported by short, low dental plates extending basally into divergent musclebounding ridges flanking a flabellate muscle field.Diductor scars large, rhomboidal, divided posteriorly by small, lanceolate adductor scars which are bisected by a short median ridge.Mantle canals lemniscate with straight, divergent vascula media.Dorsal interior with a trifid, undercut cardinal process, which is ankylosed to low, short socket plates.Bema low, subcircular, distinguished only in adult specimens, about 60 to 70% as long and 40% as wide as the valve.Inner side septa prominent, forming the inner edges of the bema in adult specimens.A short median septum and a second pair of widely divergent outer side septa are developed in some adult shells, but are not characteristic of most specimens.

Discussion.—We follow Zhan and Cocks (1998) in our interpretation of this species, described originally from the Ashgill of South China (see also Xu 1996).Our specimens differ only very slightly in their somewhat smaller size, and the poorly defined bema which is developed with certainty only in gerontic specimens.

Another similar species is Sowerbyella insueta Klenina (1984: 84 , pl.8: 8–10) from the Taldyboi Formation (upper Caradoc) of the Chingiz Range, east Central Kazakhstan, but our specimens of S. sinensis can be distinguished easily by their evenly convex ventral lateral profile, more closely spaced accentuated costellae, and in the absence of oblique rugellae along the cardinal margin.

Occurrence.—Localities 550a and 1523.