Article: A revision of Semionotus (Pisces: Semionotidae) from the Triassic and Jurassic of Europe

The morphology and taxonomic identity of Semionotus Agassiz, 1832 is clarified, and the diversity of European species of Semionotus is assessed. Confusion about Semionotus dates back to Agassiz's original description in which he based the type species, S. leptocephalus, on a single specimen, and used it to argue that the Coburg Sandstone was Jurassic, a point necessary to support his concept of the threefold parallelism in nature. The specimen disappeared shortly thereafter, and subsequent authors, concluding that Agassiz's specimen of S. leptocephalus must have been a young Lepidotes, began to recognize S. bergeri as the type species. Following an extensive search for the missing holotype of S. leptocephalus, study of relevant Semionotus material in eleven European museums, and examination of Agassiz's research notes, I argue that the holotype of S. leptocephalus must be considered lost; that Agassiz did differentiate Lepidotes and Semionotus, as evidenced by his working sketches of those two genera; and that, based on newly described skull material and Agassiz's sketches, S. bergeri should be retained as the type species (a request to that effect is now pending with the International Commission on Zoological Nomenclature).Semionotus can be distinguished from Lepidotes by the number of suborbitals; Semionotus has a single anamestic suborbital whereas Lepidotes has two or more suborbitals. Of the forty-one species of Semionotus named from European material, only four can be considered valid, suggesting that European semionotids are much less diverse than those of North America. The valid European species, S. bergeri, S. kapffi, S. normanniae, and S. minor, are redescribed.