1. The present study deals with Turbellaria, mainly from the springs of Poznań vicinity. 2. Thirty of the 43 species specified in paper are new for this region, and among them 13 are new for Polish fauna. Castrada insolida nov. spec. is described. 3. Fourty - two springs were investigated, and among them 29 from Great Poland. Nearly all of them were not large, helocrene springs. 4. In the systematicaly survey of the distribution of species, Polish localities, general ecologieal informations, morphological and taxonomical remarks, when they were needed, have been refered. Our own new data have also been included. In most cases the figures of new species to Poland are given. 5. Probably, the stands of certain species, for instance Polycelis felina, Phagocata vitta, Castrada stagnorum etc. have a relict character on Polish Lowland. 6. The fauna of Turbellaria confirm mixed nature of springs as habitat. It consists of elements of edafon, subterranean waters, small water bodies, streams and rivers and also there are occuring typical spring species. This compound nature is most distinct in helocrene springs. 7. The fauna of Turbellaria is most similar in springs laying not far one from the other, and it is less depending on other factors than zoogeographical ones. 8. The rest of the factors, which presumably influence these communities are as follows: the temperature and amount of organic matter or humus substances in a bed and water of spring. 9. The qualitative differences permit to expect that Turbellaria form in investigated springs more than a single taxocene (a group of coexisting species), but the lack of quantative data make it impossible to distingulsh them by means of Chodorowski's method.