Aspects of marine level-bottom communities are considered. Studies of entire fossil benthic assemblages and fossil level-bottom communities will make major contributions to some important biological problems and aid paleoecological and paleozoogeographic interpretations. At present these interpretations are hampered by a lack of detailed data on the ecology and distributional patterns of living species, difficulties in the interpretation of numerical counts made on fossil assemblages, and an inadequate knowledge of the mechanisms and effects of transportation on the continental shelf.