Marine coelenterates of different orders not infrequently make their way or are carried by the tide up the estuaries of rivers into brackish water, and several species have been found living in isolated lagoons and pools of which the water was distinctly salt or brackish. Among the most remarkable instances of such isolation is the occurrence in Lake Qurun in the Fayûm of Egypt of _Cordylophora lacustris_ and of the peculiar little hydroid recently described by Mr. C. L. Boulenger as _Moerisia lyonsi_ (Q. J. Micr. Sci. London, lii, p. 357, pls. xxii, xxiii, 1908). In the delta of the Ganges there are numerous ponds which have at one time been connected with estuaries or creeks of brackish water and have become isolated either naturally or by the hand of man without the marine element in their fauna by any means disappearing (p. 14). The following species have been found in such ponds:-- (_a_) _Hydrozoa._ (1) _Bimeria vestita_, Wright (1859). Hincks, Hist. Brit. Hydr. Zooph. p. 103, pl. xv, fig. 2 (1868); Annandale, Rec. Ind. Mus. i, p. 141, fig. 3 (1907). This is a European species which has also been found off S. America. It occurs not uncommonly in the creeks that penetrate into the Ganges delta and has been found in pools of brackish water at Port Canning. The Indian form is perhaps sufficiently distinct to be regarded as a subspecies. The medusoid generation is suppressed in this genus. (2) _Syncoryne filamentata_, Annandale (1907). Annandale, Rec. Ind. Mus. i, p. 139, figs. 1, 2 (1907). Both hydroid and medusæ were found in a small pool of brackish water at Port Canning. The specific name refers to the fact that the ends of the rhizomes from which the polyps arise are frequently free and elongate, for the young polyp at the tip apparently takes some time to assume its adult form. (3) _Irene ceylonensis_, Browne (1905). Browne, in Herdman's Report on the Pearl Fisheries of Ceylon, iv, p. 140, pl. iii, figs. 9-11 (1905); Annandale, Rec. Ind. Mus. i, p. 142, fig. 4 (1907). The medusa was originally taken off the coast of Ceylon, while the hydroid was discovered in ponds of brackish water at Port Canning. It is almost microscopic in size. The first two of these species belong to the order Gymnoblastea (Anthomedusæ) and the third to the Calyptoblastea (Leptomedusæ). (b) _Actinozoa._ (4) _Sagartia schilleriana_, Stoliczka (1869). _S. schilleriana_, Stoliczka, Journ. As. Soc. Beng. (2) xxxviii, p. 28, pls. x, xi (1869); _Metridium schillerianum_, Annandale, Rec. Ind. Mus. i, p. 47, pl. iii (1907).