INTRODUCTION This study was undertaken to prepare keys to the European species of the genus Trychosis Foerster. The older keys by Schmiedeknecht (1890 and 1904-1906), mostly based on Tschek's keys in his study of the genus Cryptus (1870b), do not lead to satisfactory results. This is due to the fact that several characters used by Tschek are not critical, while several of the species described by him have turned out to be identical with others. Nevertheless Tschek's pioneer work in this group deserves our admiration. When I had advanced somewhat with the interpretation of Tschek's type material, I became curious about the species described by some other authors, viz. Thunberg, Gravenhorst and Thomson. I had the opportunity to study some of their type specimens. It should be said here that probably the Gravenhorst collection at Wroclaw (Poland) still has some surprises in store, but I had no opportunity to study the collection in situ. There still remain some species inquirendae, these are listed on page 39. ACKNOWLEDGEMENTS It is a pleasure to thank the following persons : Dr. Max Fischer, Naturhistorisches Museum, Vienna, for loan of the Tschek Trychosis collection; Mr. Sten Jonsson, Uppsala Universitet, for loan of a Thunberg type specimen; Mr. W. J. Pulawski, Zoological Institute, Wroclaw, for loan of several Gravenhorst type specimens; Fil. lic. Hugo Andersson, Dept. of Entomology, Lund University, for loan of C. G. Thomson's Goniocryptus type material; Dr. Borge Petersen, Universitetets Zoologiske Museum, Copenhagen, for loan of C. G. Thomson's type material; Dr. Henry Townes,