There are more than twenty species in the genus Neomysis Czerniavsky, of which the only British representative is N. integer (Leach). This is one of the commonest species of mysids round the coasts of Britain. It lives in estuarine, brackish-water situations and Tattersall & Tattersall (1951) have summarized its distribution. The present investiga- tion has added many records from the west coast lochs of Scotland: Lochs Striven, Riddon, Fyne, Gilp, Ranza in the Firth of Clyde; Lochs Craignish, Feochan, Etive, Creran, Shuna, Linnhe, Eil and Torridon farther north. The biology of Neomysis species is much better known than that of species in other genera:N. americana (Smith) has been studied by Cowles (1930), Whiteley (1948), Hulburt (1957) and Hopkins (1965); the biology of N. awatschensis (Brandt) has been examined by Ii (1964) and Turner & Heubach (1966), that of N. czerniawskii Derjavin and N. intermedia (Czerniavsky) by Ii (1964), that of N.japonica Nakazawa by Ishikawa & Oshima (1951) and Ii (1964), that of N. rayii (Murdoch) and N. spinosa Nakazawa by Ii (1964).