The writers who are engaged in the work of giving us an account of the different kinds of Butterflies and Moths inhabiting North America, seem to fall into two categories with respect to their ideas of classification. As in other departments of Natural Science, the Entomologists differ principally in their conception of what constitutes a genus. They are either lumpers, making their genera very wide, or splitters, making their genera restricted and dependent upon less conspicuous details of structure.