BIOLOGY.--_S. crassissima_ is usually found near the surface in shallow water. Attached to the roots of the floating water-plant _Pistia stratiotes_ it assumes a spherical form, while on sticks or like objects it is spindle-shaped. Sometimes it is found growing on the same stick or reed-stem as _S. carteri_, the two species being in close contact and _S. carteri_ always overlapping _S. crassissima_. The dark colour is due to minute masses of blackish pigment in the cells of the parenchyma. The dense structure of the sponge is not favourable to the presence of _incolæ_, but young colonies of the polyzoon _Plumatella fruticosa_ are sometimes overgrown by it. Although they may persist for a time by elongating their tubular zooecia through the substance of the sponge, they do not in these circumstances reach the same development as when they are overgrown by the much softer _S. carteri_. _S. crassissima_ is found during the "rains" and the cold weather. In Calcutta it attains its maximum size towards the end of the latter season. In spite of its hard and compact skeleton, the sponge does not persist from one cold weather to another. A curious phenomenon has been noticed in this species, but only in the case of sponges living in an aquarium, viz. the cessation during the heat of the day of the currents produced by its flagella. Subgenus C. STRATOSPONGILLA, _Annandale_. _Stratospongilla_, Annandale, Zool. Jahrb., Syst. xxvii, p. 561 (1909). TYPE, _Spongilla bombayensis_, Carter. Spongillæ in the gemmules of which the pneumatic layer is absent or irregularly developed, its place being sometimes taken by air-spaces between the stout chitinous membranes that cover the gemmule. At least one of these membranes is always present. The gemmule-spicules lie in the membrane or membranes parallel to the surface of the gemmule, and are often so arranged as to resemble a mosaic. The gemmules themselves are usually adherent to the support of the sponge. The chitinous membrane or membranes are often in continuity with a membrane that underlies the base of the sponge. The skeleton is usually stout, though often almost amorphous, and the skeleton-spicules are sometimes sausage-shaped. Sponges of this subgenus form crusts or sheets on solid submerged objects. _Stratospongilla_ is essentially a tropical subgenus, having its head-quarters in Central Africa and Western India. One of its species, however, (_S. sumatrana_*, Weber) occurs both in Africa and the Malay Archipelago, while another has only been found in S. America (_S. navicella_, Carter). Aberrant species occur in China (_S. sinensis_*, _S. coggini_*) and the Philippines (_S. clementis_*). Three species have been found in the Bombay Presidency and Travancore, one of which (_S. bombayensis_*) extends its range eastwards to Mysore and westwards across the Indian Ocean to Natal. 12. Spongilla indica*, _Annandale_.