The need of a better knowledge of the acutal structure of butterflies among those in this country who follow their study, is shown by the persistence with which an antiquated classification is adhered, to,— a classification whose only value is historical, which coceals affinities and takes no account of the progress of investigation. In the hope of stimulating the examination of objects and not of books, the following Table for the determination of the four families of butterflies, originally prepared for my forthcoming work on the New England species, is here published.