(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.
Biology. The external form of the sponge is due in great part to its environment. Specimens on small stones from the bottom of the Kumaon Lakes consist of thin disk-like films, often not more than a few centimetres in diameter and a few millimetres thick: others, growing on thin twigs, are elevated and compressed, resembling a cockscomb in appearance, while others again form nodules and masses of irregular form among the branches of delicate water-weeds. Some of these last are penetrated by zoaria of Fredericella indica.
Weltner has published some very interesting observations on the seasonal variation of minute structure in European representatives of the species (Arch. Naturg. Berlin, lxxiii (i), p. 273 1907) and has discussed the formation of the abnormal spicules that sometimes occur (ibid. lxvii (Special Number), p. 191, pls. vi, vii, figs. 27-59, 1901).
Genus CORVOSPONGILLA (p. [122]).
After Corvospongilla burmanica, p. 123, add a new species:—