Genus Atrytonopsis of the American Southwest and Mexico includes the distributionally anomalous species Atrytonopsis hianna of the eastern United States, which has given rise to a species that is, in addition, ecologically anomalous (not just for its genus but for US hesperiids generally): Atrytonopsis quinteri new species lives in sand dunes along a 50-km stretch of two North Carolina barrier islands (Bogue Banks and Bear Island) and on nearby man-made Radio Island. The oviposition site and larval foodplant of this skipper is the coastal grass Schizachyrium littorale, which thrives in the rigorous sand dune habitat. Atrytonopsis quinteri is bivoltine and locally abundant. Courtship can be cursory; larvae go through 6 instars; and adults have a notably distinctive facies but variable genitalia like those of A. hianna (except that some A. quinteri females more frequently express an extreme genitalic variant). Genitalia of this pair of species differ somewhat from those of their congeners, most of which are illustrated. Among these, female genitalia show that A. margarita revised status is a species separate from its current senior synonym, A. python. Atrytonopsis quinteri and A. hianna are geographically close to each other: at one point the intervening gap (mostly water and marsh) is no more than 5 km.