ABSTRACT
A major systematic revision of Mesozoic and Cainozoic Rhynchonellida based on generic diagnostic characters, and their geographical and stratigraphical distributions, resulted in the classification adopted in the Treatise on Invertebrate Paleontology, Part H (Revised), Volume 4, which comprises 24 families grouped into seven superfamilies, namely: Dimerelloidea, Norelloidea, Pugnacoidea, Wellerelloidea, Rhynchotetradoidea, Rhynchonelloidea and Hemithiridoidea. Taxonomic units recognised by characteristic combinations of external and internal anatomical features are summarily reviewed up to subfamily level, and their main evolutionary relationships are sketched.
