The Middle Triassic bivalve genus DaonellaMojsisovics, 1874a has great potential for biostratigraphic correlation but a coherent systematic classification is still lacking. Many taxonomic characters previously used for Daonella classification depend on preservation and ontogeny, or intercorrelate strongly. The subgenus Daonella (Arzelella) Turculet, 1972 is revised on the basis of newly defined taxonomically significant characters and principle component analysis (PCA). Several species of this subgenus have been previously discriminated by characters taxonomically irrelevant such as the costae-free triangular fields adjacent the hinge (dependent on preservation), or they represent juvenile growth stages, which for instance show a more elongate shell form and no trifurcation of primary costae.
The use of this new systematic approach permits synonymy of many species with local distributions. The following species are considered as junior synonyms of D. (A.) tyrolensisMojsisovics, 1874a: D. anastasiuiKittl, 1908; D. arzelensisKittl, 1912; D. badioticaMojsisovics, 1874a; D. loczyiKittl, 1912; D. parthanensis (Schafhäutl, 1863) partim; D. cf. tyrolensisKittl, 1912; and D. tripartitaKittl, 1912. Additionally, D. imperialisKittl, 1912 is considered a junior synonym of D. (A.) taramelliiMojsisovics, 1874a. D. desecata (Schafhäutl, 1863) and D. framiKittl, 1907 have been excluded from the subgenus Daonella (Arzelella). With knowledge of precise stratigraphic distribution in classical sections, a detailed supraregional biostratigraphic correlation becomes possible, in particular for the Southern Alps of Europe.