| Summary: | Two measured sections of the upper Silurian Douro Formation from Devon Island, N.W.T. were examined for their faunal content with emphasis on the paleoecology and taxonomy of the fauna. Atrypella is believed to have lived with its beaks embedded in the muddy substrate of a somewhat restricted environment. Intermittent, low velocity currents caused disarticulation within the members of the Atrypella community and resulted in members of adjacent communities being swept in. The Atrypella Community has low faunal diversity and high density; the bulk of the Community being composed of Atrypella app., Protathyris spp. and Howellella sp. A crude zonation exists within Atrypella spp. from Arctic Canada, but more precise age dating, perhaps utilizing conodonts, is needed to clear up uncertainties. From this study, Atrypella spp. was found to be restricted to the Ludlow and Pridoli stages of the Silurian System in both North America and Eurasia. In latest Wenlock or earliest Ludlow time, two broad lineages of Atrypella evolved possibly from Cryptatrypa. One lineage was characterized by forms similar to and including A. scheii (Holtedahl). The second lineage was characterized by forms similar to and including A. prunum (Dalman). In late Pridoli time, conditions favourable for the existence of Atrypella spp. began to deteriorate and by the end of Pridoli time, both lineages had become extinct.
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