Opercula of Paleozoic gastropods are rarely found together in great numbers and may occur separated from their shells, making their identification with a particular species or genus uncertain. An unusually large collection of 27 opercula from one locality in the Lower Silurian (Llandoverian) of Quebec permits documentation of their variation and ontogeny. Comparisons of these opercula with previously reported specimens from Gotland indicate that the operculum of Oriostoma can be distinguished by its unique sculpture. The exterior surface of Oriostoma has counterclockwise multispiral coiling, whereas the interior has an opposing counterclockwise paucispiral coiling.

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