The habitat, diet, life history, and reproductive cycle of Retusa obtusa were investigated over a period of years in a population found in the Inner Harbour at Barry, Glamorgan, U.K. A technique was devised for extracting Retusa from the mud of this area.

The development of Retusa obtusa (Montagu 1803) from uncleaved egg to hatching is described. Cleavage is spiral and holoblastic, and results in the formation of a stereoblastula. Gastrulation occurs partly by epiboly and partly by invagination. The veliger

Gizzard contents indicated that youngest and oldest Retusa obtusa (Montagu) fed on foraminiferans during April–June but that increasing numbers of growing young ate increasing sizes of Hydrobia ulvae (Pennant) from July into autumn. Mean shell length