1. The genus Stomatophora is closely related to other Monocystid parasites of earthworms, but differs from them in the possession at the anterior end of the body of a sucker like epimeritic organ with a central niucron. This epinierite of Stomatophora is capable of undergoing alterations in form during the life of the parasite, and it is not abandoned inside a cell of the host as it is in Cephalina. This difference in behaviour is undoubtedly associated with tho fact that the growing trophozoite is not fixed to a single epithelial cell, but lies surrounded by the cells in a cavity which contains abundant nutrient material which it can absorb.
2. Two species of the genus have been described before and a third is now added. In Stomatophora simplex sp. nov. the sucker is not surrounded by a crown of petals.
3. A revision of the classification of Eugregarinae is suggested.