Three hypotheses have been proposed to explain the occurrence and functional significance of columellar folds in gastropods. These hypotheses suggest columellar folds; 1, increase available attachment area for the columellar muscle; 2, are deposited by an over-large, folded mantle; and 3, reflect the presence of a siphonal notch in the aperture. In order to evaluate these hypotheses we dissected and studied four species of Recent turritelliform Gastropoda. On the basis of observations made in those dissections and other information we reject all three hypotheses. As an alternative, we suggest that the columellar fold of turritelliform species delineate spiral grooves which function to prevent lateral shifting of the columellar muscle when the muscle is contracted.--Modified journal abstract.