? _Ephydatia fluviatilis_, Lamouroux, Encyclop. Méthod. ii, p. 327 (1824). _Spongilla fluviatilis_, Bowerbank (_partim_), Proc. Zool. Soc. London, 1863, p. 445, pl. xxxviii, fig. 1. _Ephydatia fluviatilis_, J. E. Gray (_partim_), Proc. Zool. Soc. London, 1867, p. 550. _Meyenia fluviatilis_, Carter (_partim_), Ann. Nat. Hist. (5) vii, p. 92, pl. vi, fig. 11 _a_, _b_ (1881). _Ephydatia fluviatilis_, Vejdovsky, Abh. k. Böhm. Gesellschaft Wiss. xii, p. 24, pl. i, figs. 1, 2, 7, 10, 14, 19 (1883). _Ephydatia fluviatilis_, _id._, P. Ac. Philad. 1887, p. 178. _Meyenia fluviatilis_ var. _gracilis_, Potts, _ibid._, p. 224. _Meyenia robusta_, _id._, _ibid._, p. 225, pl. ix, fig. 5. _Ephydatia fluviatilis_, Weltner, Arch. Naturg. Berlin, 1895 (i) p. 122. _Ephydatia robusta_, Annandale, Journ. As. Soc. Bengal, 1907, p. 24, fig. 7. _Ephydatia fluviatilis_, Weltner, in Brauer's Süsswasserfauna Deutschlands xix, Süsswasserschwämme, p. 185, figs. 316, 317 (1909). _Ephydatia fluviatilis_, Annandale, P. U. S. Mus. xxxviii, p. 649 (1910). [Many more references to this common species might be cited, but those given above will be sufficient.] This species only differs from _E. meyeni_ in the following characters:-- (i.) there are no bubble-cells in the parenchyma; (ii.) there is less spongin in the skeleton, which is less compact; (iii.) the gemmule-spicules are longer, the shafts being as a rule longer than the diameter of the rotulæ; (iv.) the gemmules are armed with a single row of regularly arranged spicules embedded in pneumatic tissue with minute air-spaces. The sponge is a variable one and several "varieties" have been described from different parts of the world. My Indian specimens come nearest to the form described by Potts as _Meyenia robusta_, but have rather more slender skeleton-spicules and more elongate gemmule-spicules. The latter also appear to be less frequently "monstrous." TYPE ? GEOGRAPHICAL DISTRIBUTION.--_E. fluviatilis_ is widely distributed in Europe and occurs in N. America,[BP] S. Africa (var. _capensis_, Kirkpatrick), Australia, and Japan. Specimens were obtained by Mr. Kemp from several lakes in Kumaon, namely Naukuchia Tal (alt. 4200 feet), Bhim Tal (4450 feet), Sat Tal (4500 feet), and Naini Tal (6300 feet). The gemmules from Bhim Tal referred by me to _E. robusta_ (Potts) also belong to this species. [Footnote BP: Most of the forms assigned by Potts to this species belong to the closely allied _E. mülleri_ (Lieberkühn).]