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|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Orthida - Draboviidae
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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.
|F. R. C. Reed 1917||Shell semielliptical to subquadrate, unequally biconvex ; hinge-line rather less than maximum width ; cardinal angles subrectangular to obtuse. Pedicle-valve deepest at beak, conical, with somewhat flattened surface ; beak forming apex of cone, not incurved, the margins of hinge-area meeting at beak at very obtuse angle (about 130°-140°); hinge-area large, flat, triangular, steeply inclined to plane of valve, with narrow median delthyrium. Brachial valve gently convex, with weak median depression usually present; beak small, inconspicuous, not rising above hingeline; hinge-area narrow, steeply inclined.
Surface of valves covered with small rather unequal closely placed ro'unded threadlike lines increasing in number by intercalation more than once, every second or third or fourth line rather stronger than the others, and all arched back slightly on lateral portions of valves; 3—4 strong concentric lamellose growth-ridges usually present near margin, and fine concentric striation over rest of surface.