Velacumantus australis is a common mollusc along the easter and southern coast of Australia. A study of the incidence of larval trematodes in several populations of V. australis showed that the incidence of the various infections varied considerably with time and place. Heterophyids were usually the commonest infection, while schistosomes and echinostomes were frequently absent. In one population, seasonal changes in the incidence of philophthalmids and schistosomes were found to be positively correlated, and seasonal changes in the incidence of philophthalmids and echinostomes were found to be negatively correlated. These results are discussed.
* School of Public Health and Tropical Medicine, Sydney University. Most of the data presented were collected while the author was at the University of New South Wales. Present address, Zoology Department, Australian National University, Canberra, A.C.T.