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Sowerbyella (Sowerbyella) varicostellata
Strophomenata - Strophomenida - Sowerbyellidae
It was recombined as Sowerbyella (Sowerbyella) varicostellata by Candela and Harper (2014).
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|G. A. Cooper 1956||Shell small, width at hinge not quite twice the length; anterior margin broadly rounded; lateral margins gently convex. Cardinal extremities acute, subalate. Posterior margin nearly straight. Surface marked by costellae of unequal size that appear in 4 generations. On the pedicle valve the median castella of the first generation is the strongest one and has the greatest size and height. On each side of this castella the flanks are marked by 2 to 3 first generation costellae that extend from the beak to the front margin. Within the areas marked off by these major costellae 3 generations of costellae may be counted. The second generation is almost of the same size as those of the first generation. These 2 generations of costellae separate 2 to 7 of the finer costellae ; 14 to 16 costellae may be counted in 2 mm. at the front of a specimen of average size.
Pedicle valve of even and moderately strong convexity ; most convex portion at about the middle. Anterior profile unevenly convex with the greatest convexity at the middle and with the sides fiat and sloping moderately to the margins. Beak inconspicuous, protruding very slightly beyond the posterior margin. Umbo narrowly swollen and passing into the swollen midregion. Slopes to the cardinal extremities very slight concave, gentle. Anterolateral regions somewhat swollen, occasionally with an obscure plication defined by the strong costellae. Interarea slightly curved, apsacline.
Brachial valve moderately convex with the greatest convexity located at about the middle and decreasing anteriorly and laterally. Flanks bounding most concave portion gently convex and with the convexity decreasing most rapidly laterally. Cardinal extremities deflected slightly toward the pedicle valve. Interarea short and hypercline.
Interior: Pedicle valve with median ridge short, extending for about onequarter the length; diductor scars deeply impressed, strongly thickened along their inner margins. Outer margins strongly thickened. Internal surface strongly spinose. Brachial valve with median ridge unusually strong; lateral septa low; none of the septa strongly elevated at the front. Median elevation of valve moderately strong, thickened at the front and with several spinous processes projecting anteriorly from the front.
|A. Williams 1962||Small, concavo-convex Sowerbyella with a medianly arched pedicle valve and gently sloping lateral areas; pedicle valve semi-oval in outline, with slightly acute cardinal extremities and less than twice as wide as long; ornamentation finely costellate, averaging about 8 or 9 per millimetre anteromedianly, with strongly accentuated primary costae.|