|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||Age range and collections|
Rhynchonellata - Atrypida - Atrypinidae
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 and T.L. Modzalevskaya 1997||Biconvex shell with sub-circular to slightly transverse outline, sometimes with extended alae, fine ribs and closely spaced uniform concentric growth filae. Maximum width near the cardinal margin. Ventral valve more convex centrally; without well-developed sulcus, but with a gently plicate anterior commissure. Beak straight or slightly incurved with submesothyridid foramen confined by small deltidial plates. Dorsal valve with uniform convexity without fold but sometimes with a shallow furrow posteriorly. The rounded to rectangular tongue is well represented on adult shells. Surface ornament of fine rounded ribs (38--48 along the anterior and lateral margins) which are increased mainly by bifurcations. Fine, closely spaced uniform concentric growth lines well preserved anteriorly. Ventral interior characterized by short, thin dental plates and stout massive teeth. Dorsal high stout myophragm elevated above the discrete cardinal plate for a short distance (Text-fig. 8). Muscle field weakly impressed.|