In 1930 Ray published a valuable paper on the genus Selenidium Giard, in which he described sporogony in S. spionis Koll. and S. foliatum Ray. He did not observe schizogony in either of these two, but he confirmed Brasil's account of intracellular schizogony in S. caulleryi Brasil from Protula tubularia Mont, and recorded it for the first time in S. mesnili Brasil from Myxicola infundibulum Mont. After seeing association of gametocytes in both these species he was unable to continue his observations, so I have taken up the work where he left it, choosing S. mesnili rather than S. caulleryi, since it is more easily obtainable. My search for gamete and sporozoite formation has been successful, but I have not been able to make the sporozoites hatch, or in studying sections of Myxicola have I seen sporozoites entering the epithelial cells of the gut.