This paper deals principally with the classification of the bees of the genera Halictus and Andrena collected during a five-year project on the pollination of the apple in the Annapolis-Cornwallis Valley, Nova Scotia. Keys for the separation of the species concerned are given, together with figures of the eighth and ninth abdominal sterna of the males, which were found very useful in separating related species. One new species, Andrena kalmiae Atwood, and the true male of A. ceanothi Vier., are described, and a re-description of Halictus arcuatus Rob. is given, including a summer form which is presumably sterile. The taxonomic section is prefaced by brief notes on economic importance and biology of the genera.