Collections of snails were made during spring, summer and fall of 1963 along the Ottawa River in the vicinity of Ste. Anne de Bellevue, near Montreal, Quebec. This area is inhabited by muskrats and frequented by many migratory birds. The river contains an abundance of fish and frogs, making it an ideal place for this study. One species of snail, Lymnaea catascopium pallida (Adams) is abundant in this area and harbours many species of larval trematodes. An intensive investigation of this species of snail revealed that only cercariae belonging to the following genera: Cotylurus flabelliformis (Faust, 1917) Van Haitsma, 1931, Diplostomum flexicaudum (Cort and Brooks, 1928) Van Haitsma, 1931, Echinostoma revolutum (Froelich, 1802) Looss, 1899, Plagiorchis muris Tanabe, 1922 and P. proximus Baker, 1915, were present in any numbers.