ABSTRACT. A large, uni- or multinucleate vampyrellid rhizopod, Lateromyxa gallica n. g., n. sp., has been isolated several times from two lakes in central France between September 1973 and August 1989 and cultivated for several months or years under laboratory conditions. No essential variations of feeding behaviour were found over the time; all isolated strains invade the trichomes of the green alga Oedogonium and move, divide and encyst inside the vanished plant cells. Penetration is performed by attacking the cross walls and only primary attacks are directed against the lateral cell walls of the algae. These findings contrast with the behaviour, life cycles and fine structure of all known species of the genera Vampyrella, Hyalodiscus, Arachnula and Gobiella. The establishment of a new genus, Lateromyxa, with the type species Lateromyxa gallica is therefore proposed.