This paper traces the development of a new bed of cockles (C. edule) in the Bassin d'Arcachon, France. Details of the basin, numbers of cockles at various times of the year, growth, fishery and competition with mytilus edulis are considered under general headings and results are presented graphically: Main Shore Beds, March 1968 to March 1969; Development of the beds over that year; The Lagoon Bed, April 1969 to April 1970. Discussion relates to possible survival and exploitation of the beds.