The taxonomic meaning of the morphological features of helminths is of paramount importance for their differential diagnostics. However, they should not be conceived as absolute, especially wih regard to trematodes such as P. daubneyi and P. microbothrium, similar not only on the basis of their morphological features but also with regard to their ultimate host-receivers as well as their geographical spreading. It is pointed out that for the differentiation of the above two types one has to take into consideration the specificity of their osculant host-receivers. As an osculant host-receiver for P. microbothrium we can consider the mollusks of the type Bullinidae (Bullinus tropicus and others, which are not to be met with in this country), as for P. daubneyi--the mollusks of the type Limnaeidae (mainly Galba truncatula--wide-spread in this country). By virtue of the above-said, it should be adopted that the cattle and the sheep in this country are invaded not by the type P. microbothrium, but by the type P. daubneyi.