The following study of Diapterna is based upon the availabile types together with material in the Museum of Comparative Zoology and in the Canadian National and Owen Bryant Collections. The collections of F. S. Carr and J. B. Wallis have also been studied. Most of the characters presented by the species are not well adapted for use in keys, and many of them vary within the species. However, material can be readily and accurately determined without reference to the genitalic characters which, though often feeble, are very constant. It will be noted that the form of the male anterior tibial spur is characteristic in each species. In the descriptions which follow, no mention is made of this spur except a note as to whether or not the apex is turned caudad, a very important feature not shown in the accompanying figures.