Abstract
Geographic distribution, species duration, and population size of 41 bivalve species which coexisted during the uppermost biozone (Sciponoceras gracile zone) of the Cenomanian were measured. Average species duration and correlation between geographic distribution, species duration, and population size were computed for five groups: total, infaunal, epifaunal, cemented epifaunal, and uncemented epifaunal bivalves.