This paper describes the non-marine Mollusca of the Pleistocene terrace deposits of Barnfield pit, Swanscombe, and discusses their ecological and climatic significance. Biostratigraphical relationships with Hoxnian deposits at Clacton-on-Sea and at certain other sites in the lower Thames basin are examined. It is suggested that the Lower Gravel and Lower Loam of Barnfield pit were formed in the early-temperate substage of the Hoxnian interglacial (zone Ho II), whereas the Middle Gravels began to accumulate not before the end of the late-temperate substage (zone Ho III), and probably extend into the early-glacial substage of the succeeding glaciation.
New evidence bearing on the dating of the Clacton Channel deposits is contained in the appendix. The Clactonian flint industry at the type site is shown to belong at least partly in subzone Ho IIb of the interglacial.