The first attempt at an arrangement of the N. Am. Lepidoptera, including a reform in the nomenclature, which I published in 1896, calls for some corrections. In the present list I have endeavoured to supply these, but, doubtless, there are others which have escaped me. Since 1896, Lord Walsingham and Mr. Durrant have fixed the types of the genera Tortrix, Tinea, Alucita and Pterophorus, in the two former confirming my doubtful determination of 1895 and correcting the type of the last named genus to monodactyla. I have followed Dyar, in Can. Ent., in using Hipocritidæ instead of Arctiidæ. I cannot find the sure type of Geometra or Noctua. I reject, however, the latter name, since it was differently used by Klein in 1753, and the assumption of 1758 as the basis of nomenclature is arbitrary. The present arrangement is based on that of the Syst. Lep. Hild., 1895. The views of Dyar with regard to the value of the larval tubercles are adopted. The superfamilies are regarded as parallel growths. It seems probable that the Hesperiades, Sphingides, Saturniades and Bombycides (Agrotides) are separate developments from the Tineid phylum. The subfamilies mark breaks in the sequence. This latter is arbitrary, but no scientific reason has been adduced for changing the general Linnæan plan, which is practically the most convenient. With regard to the family names, the oldest term, employed in a collective form and not preoccupied, is retained. At a time when new Catalogues are preparing, the publication of systems will be useful. The diurnals are arranged according to the diphyletic classification of 1897, the sequence and value of the groups are given by me in April, 1900. With regard to the origin of the Lepidoptera, the Micropterygides show hymenopteriform and trichopteriform, the Hepialides neuropteriform characteristics.