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This report outlines the preliminary results of a quantitative study of the marine animal populations in a limited area of southern California. The purpose of the project has been to conduct an intensive survey of the benthic invertebrate metazoan animals of San Pedro Basin, and to attempt a reconstruction of the natural animal associations. Many of the physical features, including temperature and salinity of the Basin, are known or are being investigated by the geologists and oceanographers of southern California. In time, therefore, the biological and physical data may be correlated and many features of distribution and abundance explained.