In their account of the fresh water molluscs of Celebes P. & F. SARASIN (1898) described the genus Protancylus. They pointed out certain resemblances between Protancylus and Ancylus as well as between Protancylus and ”Miratesta, Isidora und Planorbis”. However, they did not present any conclusion regarding the systematic position of the group. In his famous handbook THIELE (1931) placed Protancylus in the family Ancylidae. Furthermore, he regarded Protancylus as congeneric with some of the main genera of the family, e.g. Burnupia, Ferrissia, and Gundlachia. In connection with extensive studies of the family Ancylidae I had to examine the morphology and systematic position of Protancylus. As a result the genus Protancylus proper proved to be distinct from the other Ancylids and has to be removed from this family. Before I present the results of my own studies, however, it may be appropriate to briefly summarize the SARASIN’s findings. They found a well delimited hollow in each tentacle. Inside the bottom of the hollow they found a ganglion. They stated the presence of a comparatively large mantle cavity. Its inner end should be directed anteriorly, the opening more or less posteriorly though located at about the middle of the left side of the animal. Behind the mantle opening they noticed the strongly folded gill, which consists of one lamella only. They stated that the heart is anterior of the gill, what, however, is of only moderate importance as the gill is no ctenidium. The large gizzard was noticed and the radula was studied. They pointed out that the latter was more similar to the radula of certain Planorbidae than to that of Ancylus fluviatilis MüLLER. However, their information regarding the latter species was most unsatisfactory.