For many years past, those most interesting of Hymenopterous insects—the Horntails and Sawflies — have received the closest study by some of the ablest Hymenopterists of the world. Cresson and Norton, in America; Newman, Westwood, Kirby, and Cameron, in England; Klug, Hartig, and Konow, in Germany; Lepeletier and Andrè, in France; and Thompson, in Sweden, have all contributed much to our knowledge of these insects, and made decided improvements in their classification.