|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||Age range and collections|
Strophomenata - Orthotetida - Triplesiidae
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|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.