Spongilla fragilis, Leidy, P. Ac. Philad. 1851, p. 278. Spongilla lordii, Bowerbank, P. Zool. Soc. London, 1863, p. 466, pl. xxxviii, fig. 17. Spongilla contecta, Noll, Zool. Garten*, 1870, p. 173. Spongilla ottavænsis, Dawson, Canad. Nat.* (new series) viii, p. 5 (1878). Spongilla sibirica, Dybowski, Zool. Anz., Jahr. i, p. 53 (1878). Spongilla morgiana, Potts, P. Ac. Philad. 1880, p. 330. Spongilla lordii, Carter, Ann. Nat. Hist. (5) vii, p. 89, pl. vi, fig. 13 (1881). Spongilla sibirica, Dybowski, Mém. Ac. St. Pétersb. (7) xxx, no. x, p. 10, fig. 12. Spongilla glomerata, Noll, Zool. Anz., Jahr. ix, p. 682 (1886). Spongilla fragilis, Vejdovsky, P. Ac. Philad. 1887, p. 176. Spongilla fragilis, Potts, ibid. p. 197, pl. v, fig. 2; pl. viii, figs. 1-4. Spongilla fragilis, Weltner, Arch. Naturg. lix (1), p. 266, pl. ix, figs. 18-20 (1893). Spongilla fragilis, id., Arch. Naturg. lxi (i), p. 117 (1895). Spongilla fragilis, id., in Semon's Zool. Forsch. in Austral. u. d. Malay. Arch. v, part v, p. 523. Spongilla fragilis, Annandale, P. U.S. Mus. xxxvii, p. 402 (1909). Spongilla fragilis, id., Annot. Zool. Japon. vii, part ii, p. 106, pl. ii, fig. 1 (1909).
Sponge flat, lichenoid, never of great thickness, devoid of branches, dense in texture but very friable; colour brown, green, or whitish; oscula numerous, small, flat, distinctly star-shaped.
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.