A silicified rostroconch fauna is described from strata of Early (late Llandovery) to Middle (Wenlock to early Ludlow) Silurian age in the Mackenzie Mountains. Two new genera, Cassowarioides and Nehedia, and nine new species, Bigalea buskasi, B. tercierae, Bransonia foxi, Cassowarioides perryi, C. stelcki, Mulceodens schneideri, M. wilsoni, Nehedia bainsi, and N. grovesi, are proposed.An examination of the stratigraphic ranges of some of these taxa suggests that the rostroconchs may have some biostratigraphic utility during the Silurian.

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