The lower Carboniferous (Tournaisian) blastoids found at Tournai, Belgium represent the most diverse Tournaisian or Kinderhookian (Mississippian) blastoid fauna known; this fauna includes the following five genera and six species: Katoblastus Piizos (Muenster) n. gen., Katoblastus koninchi n. sp., Mesoblastus crenulatus (Roemer, Orophocrinus orbignyanus (de Koninck), Phaenoblastus caryopyllatus (de Koninck & le Hon), and an indeterminate fissiculate species. With the exception of Orophocrinus orbignyanus, the species are restricted to the environs of Tournai, although two other species of Mesoblastus are found in the lower Carboniferous (Visean) rocks of England. The Tournaisian species display a wide variety of ontogenetic patterns and functional characters. These are analyzed, and their ontogenetic development is detailed. Ecologically, the Tournaisian blastoids were part of a diverse bethonic community. One new genus, Katoblastus, type species Pentremites puzos Muenster, is proposed and one new species, K. konincki is described. The English species of Mesoblastus Etheridge & Carpenter [M. angulatus (Sowerby) and M. elongatus (Cumberland)] are described. The author suggests that M. rofei Etheridge & Carpenter and M. sowerbii Etheridge & Carpenter are junior synonyms of M. angulatus.