From the preface:
"The authors originally had intended to update their earlier edition of Freshwater Biological Association Scientific Publication No. 32 by adding supplementary notes to the existing keys, but the wealth of new information on the ecology of some groups and certain changes in taxonomy meant that the resulting text was cumbersome, and no doubt it would have been irritating for the user. Therefore a completely new key has been written, based on the previous one but with substantial changes in the keys to gammarids and crayfish. The latter now includes the common European species and transatlantic imports that increasingly may be encountered in Britain. The key to Gammarus has been shortened to include only those species that are regularly found in fresh water, as adequate keys now exist elsewhere to enable workers to identify the brackish-marine species. Other major changes in this edition are the provision of an illustrated introductory guide to the main types of malacostracans, a revised nomenclature for parts of the body, in line with modem practice, and an enlarged series of notes on taxonomy, distribution and ecology, given at the end of the keys as has been done in most of our more recent publications. This last feature has proved to be a popular addition to the FBA keys and we hope that the extensive bibliography provided here will be welcomed by all users of the key."