Evidence from numerous localities throughout the Upper Silurian strata of arctic Canada suggests that the ranges of the various species of Atrypoidea were controlled primarily by environmental factors. Atrypoidea bioherma n. sp. occurred only on and immediately around bioherms. Atrypoidea foxi inhabited subtidal areas in an offshore position, and especially those areas between the bioherms with which A. bioherma were associated. Atrypoidea phoca apparently lived in a shallow subtidal area in close proximity to the shoreline. Atrypoidea erebus inhabited environments ranging from the low intertidal to shallow subtidal. Atrypoidea netserki lived in a shallow subtidal environment close to shore.Fluctuations in bathymetry and other environmental parameters during the deposition of the Upper Silurian strata resulted in an apparent zonation of Atrypoidea species. These zones, however, are ecologically controlled and can therefore only be utilized for biostratigraphic purposes with the utmost care.