In the present study, aspects of the ecological life history of Batillaria zonalis (Brugiere) has been investigated for a period of two years. Trends in population dynamics and aspects of its biology in two salt marsh localities are described. Results of studies of the feeding biology of the sympatric population of Batillaria and Cerithidea californica (an “ecological equivalent” of Batillaria (Macdonald, 1969) and their interaction with diatoms are reported with reference to food-resource partitioning. The results are discussed within the context of problems of testing hypotheses about diversity and stability in salt marsh communities. Although these basic theoretical questions cannot be answered in this study, the Batillaria-Cerithidea-diatom component of salt marsh committees is believed to have characteristics facilitating testing of specific hypotheses about community dynamics.