During the course of breeding experiments in Ephemeroptera which we have been carrying on during the past few years, considerable nymphal and associated adult material of the genus Ephemerella has been accumulated. The main source of these collections has been the district around Knowlton, Que. where the diversified nature of the country has been particularly favorable for our studies; in addition material is also at hand from the Lachine-Taudreuil section of the St. Lawrence Valley and from the Gatineau region in the vicinity of Wakefield., Que.