As has been already stated, some authors consider _Ephydatia_ as the type-genus of a subfamily distinguished from the subfamily of which _Spongilla_ is the type-genus by having rotulate gemmule-spicules. The transition between the two genera, however, is a very easy one. Many species of the subgenus _Euspongilla_, the typical subgenus of _Spongilla_ (including _S. lacustris_, the type-species of the genus), have the spines at the ends of the gemmule-spicules arranged in such a way as to suggest rudimentary rotules, while in the typical form of _S. crateriformis_ this formation is so distinct that the species has hitherto been placed in the genus _Ephydatia_ (_Meyenia_), although in some sponges that agree otherwise with the typical form of the species the gemmule-spicules are certainly not rotulate and in none do these spicules bear definite disks. GEOGRAPHICAL DISTRIBUTION.--_Ephydatia_, except _Spongilla_, is the most generally distributed genus of the Spongillidæ, but in most countries it is not prolific in species. In Japan, however, it appears to predominate over _Spongilla_. Only one species is known from India, but another (_E. blembingia_*, Evans) has been described from the Malay Peninsula, while Weber found both the Indian species and a third (_E. bogorensis_*) in the Malay Archipelago. 16. Ephydatia meyeni* (_Carter_). _Spongilla meyeni_, Carter, J. Bomb. Asiat. Soc. iii, p. 33, pl. i, fig. 1, & Ann. Nat. Hist. (2) iv, p. 84, pl. iii, fig. 1 (1849). _Spongilla meyeni_, Bowerbank, P. Zool. Soc. London, 1863, p. 448, pl. xxxviii, fig. 4. _Spongilla meyeni_, Carter, Ann. Nat. Hist. (5) vii, p. 93 (1881). _Ephydatia fluviatilis_, Weber, Zool. Ergeb. Niederländ. Ost-Ind. i. pp. 32, 46 (1890). _Ephydatia mülleri_, Weltner (_partim_), Arch. Naturg. lxi (i), p. 125 (1895). _Ephydatia robusta_, Annandale, J. Asiat. Soc. Bengal, 1907, p. 24, fig. 7. _Ephydatia mülleri_ subsp. _meyeni_, _id._, Rec. Ind. Mus. ii, p. 306 (1908). _Sponge_ hard and firm but easily torn, usually of a clear white, sometimes tinged with green, forming irregular sheets or masses never of great thickness, without branches but often with stout subquadrate projections, the summits of which are marked with radiating grooves; the whole surface often irregularly nodulose and deeply pitted; the oscula inconspicuous; the membrane adhering closely to the parenchyma. _The parenchyma contains numerous bubble-cells_ (see p. 31, fig. 2). _Skeleton_ dense but by no means regular; the radiating fibres distinct and containing a considerable amount of spongin, at any rate in the outer part of the sponge; transverse fibres hardly distinguishable, single spicules and irregular bundles of spicules taking their place. [Illustration: Fig. 21.--Gemmule and spicules of _Ephydatia meyeni_ (from Calcutta). _a_, Skeleton-spicules; _b_, gemmule-spicules.]