The Pearl Crescent* (Phyciodes tharos) is a common New England butterfly, present in all but northern Maine. The similar Northern Crescent (P. cocyta) has a more northern distribution and was formerly considered the same species. I photographed this individual in Wells, ME.
*I've since learned that it is quite difficult to tell Pearl Crescents and Northern Crescents apart. Given the fact that both species are found in Maine, and I am not a butterfly expert, it is possible that my photos are of a Northern.