The biology of 2 species Donax incarnatus Gmelin and Donax spiculum Reeve on 2 beaches in southwest India is described. 2-year groups of Donax incarnatus were present on both beaches, from settlements during the monsoon period in 1967 and 1968. At Shertallai, both groups were studied through the year, and data on growth, mortality and production are presented. At Cochin, the rate of growth was slower and the maximum size attained smaller, but mortality during the early monsoon precluded study of Donax incarnatus through a full year. Donax spiculum occurred at Cochin mainly during the premonsoon period, and at Shertallai during the post monsoon. The species has a shorter life span than Donax incarnatus, but its irregular occurrence did not allow detailed production estimates.