In the examination of 37 clams, Musculium partumeiuzm, two have been found infected with a new species of gorgoderid cercaria for which the name Cercaria donecerca2 n. sp. is proposed. The clams were collected from a small pond near Cold Spring on Hudson, N. Y., in June, 1938. The infected clams have each produced about fifteen to twenty-five cercariae per day for one month. Studies have been made upon both living and fixed specimens, the former being more satisfactory for morphological observations. Identification of the genital primordium was possible in material treated with an aqueous solution of methyl green and acetic acid, following the application of neutral red, a technique more or less specific for reproductive anlagen.