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Strophomenata - Orthotetida - Triplesiidae
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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 (Epacroplecia)||Trigonal, unequally biconvex triplesiaceids with a highly convex, trilobate brachial valve and a shallow pedicle valve geniculated to form a median tongue complementary to the inflated median fold and lateral flanks of the brachial valve; hinge-fine very short; dorsal interarea vestigial, "chilidium" short, obtusely triangular, situated astride the posterior face of the cardinal process shaft; ventral interarea of variable length almost orthocline, pseudodeltidium entire with narrow median fold, foramen large, apical; ornamentation consisting of fine, sharp, striate-like costellae with inconspicuous concentric growth-lines, shell substance impunctate but with scattered subcircular knots of fibrous calcite occurring in the inner layer and appearing rarely at the surface as indistinct tubercles.
Dorsal interior with a massive cardinal process shaft bifurcated distally, sockets rather deep, situated lateral to a pair of strong, blade-like, subparallel brachiophores disposed normal to the hinge-line and ankylosed to it as well as to the postero-median portion of the valve floor; muscle-field obscurely impressed but associated with 4 subparallel septa symmetrically placed on either side of the median fold, with the outer pair the longer.
Ventral interior with massive teeth supported by long, narrowly divergent dental lamellae; musclefield probably extending anteriorly to the ends of the dental lamellae and divided antero-medianly by a low narrow ridge.