This manual of molluscan shell growth has been prepared so that the pollution biologist confronted with after-the-fact monitoring problems can extract information about recruitment, growth, and mortality responses of molluscs to past and present changes in environmental quality. This information is stored within individual molluscan shells in the form of ontogenetic records for growth and development: larval top shells, internal microgrowth increments, and changes in shell microstructures. An example of how internal growth increments can be used in this way is given for Mercenaria mercenaria exposed to a power plant thermal plume.