In his “Synopsis of the Aphididae of Minnesota,” Bul. 4 of the “Geological and Natural History Survey of Minnesota,” 1887, p. 62, Dr. Oestlund describes a light green aphis occurring upon Oenothera biennis , giving it the name oenotherae . The entomologists of the country seem quite generally to have attached this name to a similar, but quite distinct, species common in the eastern states, which seems to have escaped description and which apparently confines its attacks to Oenothera biennis . A large number of records on these two species indicate that the one so well described by Dr. Oestlund is extremely common on Oenothera and Epilobium species in Colorado, while the undescribed species is rarely taken in this state.