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The type species of the early Paleozoic nuculoid pelecypod genus Tancrediopsis Beushausen, 1895, is shown to be Ctenodonta contracta Salter, 1859, from Middle Ordovician rocks of southern Quebec, Canada. This species is redescribed from a series of 189 well-preserved silicified specimens, about half of which were collected at the original type locality. This large sample permits the definition of limits of variation in the species and reveals previously unknown morphologic features, among which are strong pedal muscle scars and external escutcheonal perforations. The species is easily confused with closely related sympatric species of Tancrediopsis, and criteria are discussed for distinguishing it from these similar forms. The correct name for "Ctenodonta" contracta Salter is shown to be Tancrediopsis cuneata (Hall).