Palaeoniscum (from , 'ancient' and 'cod-fish' or 'woodlouse') is an extinct genus of ray-finned fish from the Permian period (Guadalupian-Lopingian) of Europe (England, Germany, Czech Republic?, Turkey), North America (Greenland), and possibly other regions. The genus was named Palaeoniscum in 1818 by Henri Marie Ducrotay de Blainville, but was later misspelled as Palaeoniscus by Blainville and other authors (notably Louis Agassiz). Palaeoniscum belongs to the family Palaeoniscidae. The type species Palaeoniscum freieslebeni was named after Johann Carl Freiesleben (1774–1846), mining commissioner of Saxony. P. freieslebeni is the most common taxon in the Wuchiapingian aged Kupferschiefer and Marl Slate, where it constitutes 80% of all fish fossils. Palaeoniscum had a torpedo-shaped body in length, with a deeply forked caudal fin and tall dorsal fin, indicating that it was a fast swimmer. It was probably an active predator, feeding on other freshwater fish. Its sharp teeth could be replaced when lost, a trait also seen in modern sharks. Like other early ray-finned fish, Palaeoniscum had air sacs connected to the mouth, which served as a primitive swim bladder. Several Palaeozoic and Mesozoic species that have been ascribed to the genus Palaeoniscum were later shown to be only distantly related with P. freieslebeni. These species were subsequently removed and transferred to other genera (e.g., Acentrophorus, Aeduella, Paramblypterus, see list below). The allocation of other species to Palaeoniscum (see list below) is often doubtful and mostly based on superficial resemblance with P. freieslebeni. Palaeoniscum is the name giving taxon of the extinct Palaeonisciformes (or Palaeoniscoidei), a polyphyletic group comprising several superficially similar looking but not closely related early actinopterygian taxa. Palaeonisciformes is considered a wastebasket taxon by modern taxonomic standards. Species Palaeoniscum angustum (Rzehak, 1881) [Palaeoniscas angustus Rzehak, 1881] Palaeoniscum antipodeum (Egerton, 1864) [Palaeoniscus antipodeus Egerton, 1864] Palaeoniscum antiquum Williams, 1886 Palaeoniscum arenaceum Berger, 1832 Palaeoniscum capense (Bloom, 1913) [Palaeoniscus capensis Bloom, 1913] Palaeoniscum comtum (Agassiz, 1833) [Palaeoniscus comtus Agassiz, 1833] Palaeoniscum crassum (Woodward, 1908) [Palaeoniscus crassus Woodward, 1908] Palaeoniscum daedalium Yankevich & Minich, 1998 Palaeoniscum devonicum Clarke, 1885 Palaeoniscum elegans (Sedgwick, 1829) [Palaeoniscus elegans Sedgwick, 1829] Palaeoniscum freieslebeni de Blainville, 1818 (type species) [Eupalaeoniscus freieslebeni (de Brainville, 1818); Palaeoniscus freieslebeni (de Brainville, 1818); Palaeoniscus macropomus Agassiz, 1833; Palaeoniscus magnus Woodward, 1937] Palaeoniscum hassiae (Jaekel, 1898) [Galeocerdo contortus hassiae Jaekel, 1898; Palaeomyzon hassiae (Jaekel, 1898)] Palaeoniscum kasanense Geinitz & Vetter, 1880 Palaeoniscum katholitzkianum (Rzehak, 1881) [Palaeoniscas katholitzkianus Rzehak, 1881] Palaeoniscum landrioti (le Sauvage, 1890)