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|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Orthida - Dalmanellidae
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.
|L. R. M. Cocks 1982||Exterior. Shells with subcircular outline; gently convex pedicle valve without incurved umbo; convex brachial valve with gentle sulcus. Relatively small apsacline pedicle valve interarea, narrow open delthyrium, with apex angle about 40°. Small anacline brachial valve interarea, approximately half valve width; open notothyrium partly filled with posterior of cardinalia. Primary ornament of relatively fine, even costellae (approx. 5 per mm at 3 mm anteriorly) with new ribs arising by branching; secondary ornament of concentric filae (14-16 per mm throughout valve length) more accentuated in rib troughs and rarely crossing rib crests.
Pedicle valve interior. Strong teeth supported by short stubby dental plates which merge anteriorly quickly with the valve floor; small crural fossettes present. Muscle field relatively small, extending for average of 34% valve length in five specimens, bilobed, adductor scars poorly differentiated (PI. 79, fig. 17). Vascular markings usually obscure, but pair of thick vascula media diverge anteriorly from diductor scars in some specimens.
Brachial valve interior. Cardinal process relatively small, bilobed posteriorly, and continuing anteriorly in a thin shaft which merges further anteriorly with a low but distinct myophragm. Thick, stubby brachiophores which merge posterolaterally with subsidiary fulcral plates to give well-defined sockets, which are also bounded anterolaterally by thin socket plates. Tops of brachiophores diverging anteriorly at about 70°. Well-defined adductor area extending anteriorly for 50-60% of valve length; anterior scars longer and wider than posterior scars (PI. 79, fig. 13).