Middle Devonian acritarch biostratigraphy of North America

Abstract. The known stratigraphic ranges of 66 acritarch species from eight independently dated Middle Devonian sections in North America are plotted. Twenty seven species are restricted to the Middle Devonian in North America, yet only 12 species occur in more than one section. None of these 12 species is, as yet, known to occur outside North America. This apparent endemism is believed to be due partly to the lack of study of contemporaneous assemblages from elsewhere in the world.