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Rhynchonellata - Orthida - Plectorthidae
If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|G. A. Cooper 1956||Shell of about medium size for the genus, wider than long; subrectangular in outline; strongly biconvex with the brachial valve having a slightly greater depth than the pedicle one. Anterior commissure broadly uniplicate ; sides somewhat narrowly rounded. Hinge narrower than the greatest shell width ; cardinal extremities obtusely angular. Costellate ; costellae subequal in size, crowded and separated by striae of less width than the costellae. About 17 costellae in the space of 5 mm. at the front.
Pedicle valve moderately convex in lateral profile with the greatest convexity located in the posterior half, the anterior half somewhat flattened. Anterior profile broadly convex. Sulcus nearly obsolete, the only trace shown is a broad flattening in the anteromedian third of the valve. Posterolateral slopes very steep but becoming more gentle anteriorly. Anterolateral and anterior slopes gentle. Beak erect and prominent, only slightly incurved ; interarea long, apsacline.
Brachial valve strongly convex in lateral profile ; broadly convex in anterior profile. Umbo marked by a shallow and narrow depression that extends from the beak nearly to the middle of the valve. Fold obsolete, but a broad wave of the anterior margin in a brachial direction serves as a fold. Median area swollen, slopes in all directions from median area steep, but the lateral and posterolateral slopes are the steepest.
Pedicle interior with subpentagonal muscle area having long, narrow diductor scars and a broad adductor field. Median ridge of brachial valve extending about to middle. Notothyrial cavity deep, brachiophore supports strong.