_Skeleton_ with well defined radiating and transverse fibres, which are never strong but form a fairly dense network with a small amount of spongin. _Spicules._ Skeleton-spicules smooth, sharply pointed, moderately stout, as a rule nearly straight. No flesh-spicules. Gemmule-spicules cylindrical, blunt or abruptly pointed, nearly straight, covered with relatively stout, straight, irregular spines, which are equally distributed all over the spicule. _Gemmules_ bound together in free groups of varying numbers and forming a flat layer at the base of the sponge; each gemmule small in size, surrounded by a thick cellular coat of several layers; with a relatively long and stout foraminal tubule, which projects outwards through the cellular coat at the sides of the group or at the top of the basal layer of gemmules, is usually curved, and is not thickened at the tip; more than one foraminal tubule sometimes present on a single gemmule; gemmule-spicules arranged horizontally or at the base of the cellular coat. The species as a species is easily distinguished from all others, its nearest ally being the N. American _S. ingloriformis_ with sparsely spined skeleton-spicules which are very few in number, and gemmule groups in which the foraminal tubules all open downwards. Several varieties of _S. fragilis_ have been described in Europe and America. TYPE.--Potts refers to the type as being in the Academy of Natural Sciences at Philadelphia. GEOGRAPHICAL DISTRIBUTION.--All over Europe and N. America; also in Siberia, Australia, and S. America. The species is included in this work in order that its Asiatic local races may be fitly described. 9 _a._ Subsp. calcuttana*, nov. ? _Spongilla decipiens_, Weltner (_partim_), Arch. Naturg. lxi (i), pp. 117, 134 (1895). _Spongilla decipiens_, Annandale, Journ. As. Soc. Beng. 1906, p. 57. _Spongilla fragilis_, _id._, Rec. Ind. Mus. i, p. 390 (1907). [Illustration: Fig. 15.--_Spongilla fragilis_ subsp. _calcuttana_. A=group of gemmules, × 70; B=spicules, × 240. From type specimen.] This local race, which is common in Calcutta, is distinguished from the typical form mainly by the shape of its skeleton-spicules, most of which are abruptly pointed or almost rounded at the tips, sometimes bearing a minute conical projection at each end. The gemmule-spicules, which are usually numerous, are slender. The foraminal tubules are usually long and bent, but are sometimes very short and quite straight. The colour is usually greyish, occasionally brown. I have not found this race except in Calcutta, in the ponds of which it grows on bricks or, very commonly, on the stems of bulrushes, often covering a considerable area. TYPE in the Indian Museum. 9 _b._ Subsp. decipiens*, _Weber_. _Spongilla decipiens_, Weber, Zool. Ergeb. Niederländ. Ost-Ind. i, p. 40, pl. iv, figs. 1-5 (1890).