This work is intended to take the place of Smith's List of the Lepidoptera of Boreal America (1891), and to furnish a condensed catalogue of North American Lepidoptera comparable to Staudinger and Rebel's Catalogue of the Lepidoptera of Europe. With a few years several of the larger families of the Lepidoptera have been fully catalogued, so that it seemed both unnecessary and inadvisable to repeat all of this mater. To avoid this, and yet make these references easily available, a catalogue reference is given at the head of each family, abbreviated "C" and it is specifically referred to by pages or numbers. The original reference to each species is, however, always repeated, except in the case of old synonyms. All specific synonyms are included, but where the reference is not given it will be found in the Catalogue referred to.