The geographical distribution of the lower invertebrates of fresh and of stagnant water is often an extremely wide one, probably because the individual of many species exists at certain seasons or in certain circumstances in a form that is not only resistant to unfavourable environment, but also eminently capable of being transported by wind or currents. We therefore find that some genera and even species are practically cosmopolitan in their range, while others, so far as our knowledge goes, appear to have an extraordinarily discontinuous distribution. The latter phenomenon may be due solely to our ignorance of the occurrence of obscure genera or species in localities in which they have not been properly sought for, or it may have some real significance as indicating that certain forms cannot always increase and multiply even in those localities that appear most suitable for them. As an example of universally distributed species we may take the European polyzoa of the genus _Plumatella_ that occur in India, while of species whose range is apparently discontinuous better examples could not be found than the sponges _Trochospongilla pennsylvanica_ and _Spongilla crateriformis_, both of which are only known from N. America, the British Isles, and India. My geographical list of the species of sponges, coelenterates, and polyzoa as yet found in fresh water in India is modelled on Col. Alcock's recently published list of the freshwater crabs (Potamonidæ) of the Indian Empire[B]. I follow him in accepting, with slight modifications of my own, Blanford's physiographical rather than his zoogeographical regions, not because I think that the latter have been or ought to be superseded so far as the vertebrates are concerned, but rather because the limits of the geographical distribution of aquatic invertebrates appear to depend on different factors from those that affect terrestrial animals or even aquatic vertebrates. [Footnote B: Cat. Ind. Dec. Crust. Coll. Ind. Mus., part i, fasc. ii (Potamonidæ), 1910.]