Eye-witness accounts of a living “panther”, a leopard, two tigers and a hyena, appended to “Idea institutionum Trichozoologiae”, an unpublished manuscript on mammal classification by Swedish naturalist Peter Artedi (1705–1735), made during a visit to London sometime between early November 1734 and June 1735, are described. Interest is focused on his account of the hyena, which appears to have been the only modern source for Carl Linnaeus, who acknowledged Artedi in the first edition of Systema naturae. Evidence is provided to show that Artedi's account was accurate and original, having never had the opportunity to witness the animal previously.