Traces of the predation by booring gastropods, very common on the Lower Tortonian gastropods, pelecypods and scaphopods from the Korylnica clays on the southern slopes of the Holy Cross Mts, Central Poland, have been ascribed to the activity of four muricid and five naticid species. A very strong differentiation of the proneness of particular species to be attacked by predatory boring gastropods has been shown by a statistical analysis of more than 20,000 specimens of over 120 species. In this respect the character of differentation of large taxonomic and ecological groups suggest that it results not so much from the ethology of the predators as from the ecology od their potential prey. The ratio of the numbers of the naticid and muricid prey within the range of large taxonomic and ecological groups indicates divergent intrests of the two groups of predatory boring gastropods and an only small extent of competition.