Originally published in 1967, as the fourth edition of a text first published in 1939, this reference book provided the serious student of marine biology with the means of identifying the extraordinary variety of living creatures to be found on the British and Irish coasts, without the need for searching through large specialised monographs or papers scattered in zoological journals. It was written to encourage observation of the habits and structure of the living animal in its natural surroundings, supplemented by closer study in the laboratory, with special attention to characters of systematic importance, and to give preliminary training in systematic work. The keys in this book enabled the collector to trace an animal at least to its genus; and in the process learn how to carry the investigation further if need be in the specialist monographs, of which lists are given at the head of each chapter.