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|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Orthida - Plaesiomyidae
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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.
|A. Williams 1962||Large, subquadrate Dinorthis with a convex brachial valve lacking a median sulcus and even developing a slight median fold and a plane to slightly concave pedicle valve, with a convex umbo and a slight antero-median sulcus; radial ornamentation consisting of narrowly rounded ribs separated by wide interspaces, especially medianly, where their mean wave-length is just over 1 mm. at 7.5 mm. anterior to the umbo, pattern coarsely costellate with secondary branches conspicuous in sectors I to V only after the 10-mm. growth-stage; dental lamellae well developed, narrowly divergent, and forming no more than posterior boundaries to a large, subtriangular muscle-field, longer than wide and strongly elevated on a platform of secondary shell substance; cardinal process massive, lobate, with crenulated posterior face and ankylosed together with stout, rounded brachiophore bases to a narrow notothyrial platform extended anteriorly as a short median ridge; dorsal adductor scars poorly impressed, not extending anteriorly for more than one-quarter the length of the valve.|