Two disturbing trends are seen in current thinking behind the establishment of new genera of fossil brachiopods; the emphasis on their applications stratigraphi-cally, and the use of progressively finer distinctions in diagnoses. The genus is a biologically based concept and thus fossil genera are only justifiable if the basis of their establishment is also biological; any stratigraphical applications are merely a by-product. The use of finer morphological distinctions in the establishment of fossil brachiopod genera in recent years runs contrary to the findings of field zoologists working on modern marine shells. Examples of the wide morphological variation in modern shells, apparently phenotypically induced, are given, the importance of this work in keeping the genus concept of the palaeontologist in perspective is stressed, and a revision of the established taxonomy of the triple-siacean Onychotreta undertaken as an illustration.