The new edition of the Catalogue of the described Diptera of North America, by the Baron Osten Sacken, Washington, 1878, ranges doubtlessly among the most important works published on the North American Fauna. A very detailed and elaborate preface tells only in brief manner the immense amount of work done by the author since the publication of the first catalogue in 1858. A large part of new information is given at the end of the Catalogue in 335 notes.