|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Rhynchonellida - Trigonirhynchiidae
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. Outline subtriangular, with prominent erect pedicle valve beak with relatively straight sides, which often curve anteriorly to become laterally concave in outline. Small but functional pedicle opening. Variable convexity, from nearly flat to fairly globose. About twelve ribs, difficult to count laterally since they merge with the flat shell sides; ribbing stronger anteriorly from about half valve length, the ribs curving gently antero-laterally. Anterior commissure usually fairly straight, but simple fold and sulcus sometimes weakly developed.
Pedicle valve interior. Teeth supported by well-developed but slender dental plates, subparallel on valve floor, but diverging slightly dorsally. Small transverse pedicle collar weakly developed at approximately the same distance anteriorly as the teeth. Muscle field not impressed.
Brachial valve interior. Cardinal process absent. Median septum present to half or two-thirds of the valve length. Prominent socket plates extend anteriorly to form crural bases, underneath which a small crurualium is present posteriorly. Indistinct suboval impressions of adductor muscle scars present on either side of the median septum.