New collections, as well as original type material, of Lower and Middle Ordovician sponges from the Mingan Island Archipelago are described and figured from the Mingan and Romaine Formations. Archaeoscyphia minganensis (Billings, 1859), Hudsonospongia minganensis Raymond and Okulitch, 1940, H. irregularis Raymond and Okulitch, 1940, H. duplicata Raymond and Okulitch, 1940, Zittelella varians (Billings, 1861a), and Eospongia roemeri Billings, 1861, are redescribed from original type specimens and new collections. The species Archaeoscyphia pulchra (Bassler, 1927), Rhopalocoelia clarkii Raymond and Okulitch, 1940, Psarodictyum magnificum Raymond and Okulitch, 1940, and Lissocoelia ramosa Bassler, 1927 are reported and described from the Mingan Islands for the first time. To these sponges are added the new species Anthaspidella amplia, Archaeoscyphia undulata, Hudsonospongia nodosa, and Zittelella grossa, which are described from type specimens from the Mingan Formation.
The assemblage from 12 localities from the Mingan Formation, and one from the Romaine Formation, represents one of the most diverse demosponge faunas from eastern North America. Sponges in most of the localities accumulated as transported debris or lag gravels, but locally, some grew in small reefoidal mounds and also accumulated as adjacent debris.