During the months of April, May, June, and July of 1916, I examined 1,500 molluscs from the rivers and fresh-water pools of Natal. They included several species. Limnaea natalensis is a common form with a dextral shell. Physopsis africana, a common mollusc amongst decomposing vegetation, has a blunt-pointed sinistral shell with a truncate columella. Planorbis pfeifferi is a common form with a round, flat shell. Planorbis leucocheilus is not unlike it, but is much smaller. Isidora tropica is fairly common; it has a blunt-pointed sinistral shell. Isidora forskali is rarer and has a conical shell. In one brickfield I found a large number of specimens of Ancylus (ferrissia) burnupi, which has a small oval shell. Two hundred eleven specimens harbored cercariae of various kinds. Infected specimens were most common in one brickfield at Durban and in a small pool along the course of the Umsindusi River at Pietermaritzburg, which had been formed as a result of an overflow of the river. Infected specimens were most frequently met with in May and June. All of the cercariae possessed a long, slender tail; those that were found in specimens of Physopsis africana more often than not possessed divided tails. The tail was easily detached from the body of a cercaria and continued to move for some time after becoming free. All of the cercariae were distomes; the oral sucker was terminal, and in a few specimens the posterior border of the sucker was incomplete; the acetabulum was situated slightly nearer the tail end of the body. None of the cercariae had spines or stylets, and there were no projections from the body or tail. A pharynx was noted in only one form, and eye-spots were present only in cercariae from one specimen.