In previous publications Bishop & Crisp (1957, 1958) described the distribution of Elminius modestus on the coasts of France, based on surveys made in 1953 and 1954. Further information including some observations made in 1955 was given by Bishop, Crisp, Fischer-Piette & Prenant (1957). Elminius was shown to be centred on three main areas; the Channel coast east of Cap de la Hague, the river systems of North Brittany, and the Rade de Brest. Further south scattered individuals only were to be found, nowhere in sufficient abundance to allow the majority to breed. Bishop & Crisp (1957) pointed aut that the scarcity of Elminius on this part of the Brittany coast was surprising, since there are numerous suitable estuaries and harbours and an abundance of fishing craft which might disseminate the species. A further survey was made in August and September 1957. No significant changes had taken place along the coast of the Channel nor in the Rade de Brest itself. However in the vicinity of the important fishing ports of Concarneau and Lorient a marked increase in the population of Elminius had taken place between 1954 and 1957 (fig. 1). Established colonies were found in the harbour at Concarneau, and in the river systems of the Aven, Belon and Laita. The greatest abundance was found at the junction of the Scorff and Blavet near Lorient, while in the adjacent estuary of the Etel the species was quite common. Further south the only evidence of Elminius was a single specimen seen on the harbour wall at Point St. Jacques. No specimens were found anywhere in the inland sea of Morbihan, an area of sheltered water very suitable for this species, nor in the estuary of the Loire. Probably the very exposed Quiberon peninsula is for the time being a barrier to its further spread to the south.