Colonies of the rugose corals Nemistium liardense sp. nov. and Heritschioides simplex sp. nov. were collected from limestone in the upper member of the Mattson Formation in the Liard Range in the Northwest Territories and are the only known identifiable coral species from the Mattson Fm. The Mattson Fm., deposited in the Liard Basin west of the syndepositional Bovie reverse fault, comprises sandstone with subordinate shale and carbonates deposited during several delta cycles. The close morphological similarity and identical mode of offsetting in N. liardense colonies from the Mattson Fm. and the allochthonous Stikine Terrane of British Columbia indicate they belong in the same species. This and the morphological similarity between H. simplex and the late Serpukhovian to early Bashkirian H. columbicum allow assignment of the coral-bearing part of the upper Mattson Fm. to Bashkirian Foraminiferal Biozone 20. Widespread occurrence of the genus Nemistium confirms open communication between the Liard Basin region and the western European and northern African seas.

Key words: Rugosa, Stauriida, taxonomy, paleogeography, Carboniferous, Pennsylvanian, Canada.

Jerzy Fedorowski [jerzy@amu.edu.pl], Institute of Geology, Adam Mickiewicz University, Bogumiła Krygowskiego 12, 61-680 Poznań, Poland. E. Wayne Bamber [wayne.bamber@canada.ca] and Barry C. Richards [Barry.richards@canada.ca], Geological Survey of Canada (Calgary) Natural Resources Canada/Government of Canada 3303-33rd Street Northwest, Calgary, Alberta T2L 2A7, Canada.