Two large cratonic interior basins, the Williston and Hudson, were situated within the Red River-Stony Mountain Solitary Coral Province, which occupied most of North America during Late Ordovician time. Helicelasma selectum (Billings, 1865), Deiracorallium angulatum gunni n. subsp., Lobocorallium trilobatum trilobatum (Whiteaves, 1895), and Bighornia cf. B. patella (Wilson, 1926) are known from the Stony Mountain Formation of southern Manitoba. The presence of identical species in Saskatchewan and Wyoming suggests that one assemblage inhabited the Williston Basin. The Hudson Basin assemblage comprises species that also occur in the Williston Basin, species closely resembling Williston Basin forms, and taxa that do not occur in the Williston Basin. Solitary Rugosa within the Red River-Stony Mountain Province in eastern North America are most closely related to those of the Williston Basin. Studies of Ordovician solitary Rugosa suggest that cratonic interior basins were centers of evolution, diversification, and dispersion.--Modified journal abstract.