The morphological diversity within the species Echinogammarus berilloni (Catta, 1878), stressed by Spandl (1926), Margalef (1956) and Pinkster (1969) was a motive to sample systematically in drainage systems of the Iberian peninsula and of great parts of France. It became clear that E. berilloni in reality was the collective name for a group of at least 10 species, all of them with their own, restricted distribution area. Only one of these species, the real E. berilloni, inhabits a much larger area, including the major part of France, the Channel islands, Belgium, Luxembourg, the southern part of the Netherlands, and south-western Germany. In this study the characters of the E. berilloni-group are discussed and comparative descriptions are given of all species, along with a key for their identification. The variability and ecological preferences of each species are discussed. An attempt has been made to relate the distribution pattern of this group and of other species groups in the Iberian peninsula (e.g. the E. simoni-group, members of the G. pulex-group, and the genus Eulimnogammarus) to geological data.