|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Orthida - Archaeorthidae
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||Large, subquadrate Cyrtonotella less commonly with an alate hinge-line, profile gently concavo-convex with a broad, low sulcus in the brachial valve tending to become obsolescent anteriorly, brachial valve slightly more than two-thirds as long as wide; shell surface costellate in four generations and commonly finely developed and closely spaced at 10 to 13 per 5 mm. antero-medianly, exceptionally as coarse as 7 costellae per 5 mm. ; ventral muscle-scar squat, about three-quarters as long as wide and extending anteriorly for less than one-third the length of the valve, median adductor scar narrowly lanceolate, enclosed by diductors which extend anterior to them as a pair of narrow impressions passing into vaguely impressed vascula media; cardinal process bulbous, notothyrial platform broad and low, brachiophores subparallel with hinge-line.|