Some years ago I proposed the generic name Glaucopsyche for a group of blue butterflies of eastern N. America having a glaucous sheen to the upper surface of their wings; I had not then recognized its strictly generic alliance with a group of similar forms in Europe and on our pacific slope, which do not all possess this peculiarity, and to which the older generic name Nomiades Hübn. must be applied. A recent study of their common structural features, however, shows that GlacoPsychw can no longer be retained.