When, in 1917–18, I made a microscopic examination of freshwater snails at Potchefstroom, Transvaal, I found 10 per cent, of the examples of Isidora schackoi Jickeli infested with eye-spotted cercariae which Dr E. C. Faust recognised as amphistomes. Some shells which I collected from the same pools and considered to be immature examples of Isidora schackoi have been identified as Sericima. It is possible that the two species are identical. I found Isidora forskali at Cato Manor, outside Durban, infested with amphistomes, and confirmed this observation by isolating similar cercariae from the same freshwater snail on the Umgeni flats. I have obtained examples of Isidora forskali from Amanzimtoti, Isipingo, Clairwood, Umhl-a-tazana, Cato Manor, Inchanga station, Umgeni, Tongaat, Nonoti, Umzindusi, at Pietermarizburg, Lourenço Marques and Beira. These places constitute several new localities for the species and no Isidorae had previously been recorded from Beira. This mollusc is common in small shallow spruits and is often attached to small plants or water-lily leaves. It is seldom more than 10 mm. in length.