Since the appearance of the article on the difficult truncata-citrata group of this genus by Swett (1917, Can. Ent., XLIX,, 64) and by Barnes and McDunnough (1917, Contr., III, (4), 227, Pls. XXI, XXX; 1918, Contri., IV, (2), 137) little has been published concerning the North American representatives with the exception of the addition of a couple of new form-names by Wright and Blackmore. In the European literature several important papers, however, dealing with the Palaearctic species of the genus, have appeared; chief among these is the very comprehensive Monograph of the Palaearctic Species by Dr. P. Heydemann (1929, Mitt. Munch. Ent. Gesells., 207-292, Pls. I-XV) copiously illustrated with figures of the adults and of the genitalia, both male and female.