SYNOPSIS. Dactylosoma is a genus of blood protozoa which undergo schizogony, without producing pigment, in the red cells of the lower vertebrates, especially amphibia. The best known species is D. ranarum, but even for this species the life cycle, except as it occurs in the erythrocyte, and the vector remain unknown. Study of slides from the blood of two species of Formosan frogs, Rana guentheri and R. limnocharis, revealed Dactylosoma ranarum in the former, and what appeared to be a new species, for which the name Dactylosoma taiwanensis is proposed, in the latter. Rana limnocharis has not previously been known to be a host of Dactylosoma, nor has this genus of parasite been reported from Formosa. Dactylosoma ranarum, though not known from many species of frogs and toads, occurs in Asia, Africa, Europe, and in Central and South America. This suggests that it must have been a parasite of Anura for a very long time. Since frogs and toads are incapable of long migrations and are very intolerant of salt water, so wide a distribution may also have palaeogeographic significance.