TYPES. The types of the species and of the var. _cerebellata_ are in the British Museum, with fragments of the former in the Indian Museum; that of var. _bengalensis_ is in the Indian Museum, with a co-type in London. GEOGRAPHICAL DISTRIBUTION.--India And Egypt. _Localities_:--BOMBAY PRESIDENCY, island of Bombay (_Carter_); Igatpuri, W. Ghats (_Annandale_): BENGAL, Calcutta; Port Canning, Ganges delta (var. _bengalensis_) (_Annandale_); Garia, Salt Lakes, nr. Calcutta (var. _bengalensis_) (_B. L. Chaudhuri_); Chilka Lake, Orissa (var. _bengalensis_) (_Gopal Chunder Chatterjee_): MADRAS PRESIDENCY, Rambha, Ganjam district (_Annandale_): NIZAM'S TERRITORY, Aurangabad (_Bowerbank_, var. _cerebellata_). The var. _cerebellata_ has also been taken near Cairo. BIOLOGY.--The typical form of the species is usually found growing on rocks or bricks at the edges of ponds, while the variety _bengalensis_ abounds on grass-roots in pools and swamps of brackish water in the Ganges delta and has been found on mussel-shells (_Modiola jenkinsi_, Preston) in practically salt water in the Chilka Lake. Carter procured the typical form at Bombay on stones which were only covered for six months in the year, and "temporarily on floating objects." In Calcutta this form flourishes in the cold weather on artificial stonework in the "tanks" together with _S. carteri_, _S. fragilis_, _Ephydatia meyeni_, and _Trochospongilla latouchiana_. The variety _bengalensis_ is best known to me as it occurs in certain ponds of brackish water at Port Canning on the Mutlah River, which connects the Salt Lakes near Calcutta with the sea. It appears in these ponds in great luxuriance every year at the beginning of the cold weather and often coats the whole edge for a space of several hundred feet, growing in irregular masses which are more or less fused together on the roots and stems of a species of grass that flourishes in such situations. Apparently the tendency for the sponges to form branches is much more marked in some years than in others (see Pl. I, figs. 1-3). The gemmules germinate towards the end of the "rains," and large masses of sponge are not formed much before December. At this season, however, the level of the water in the ponds sinks considerably and many of the sponges become dry. If high winds occur, the dry sponges are broken up and often carried for considerable distances over the flat surrounding country. In January the gemmules floating on the surface of the ponds form a regular scum. _S. alba_ var. _bengalensis_ is the only sponge that occurs in these ponds at Port Canning, but _S. lacustris_, subsp. _reticulata_, is occasionally found with it on brickwork in the ditches that drain off the water from the neighbouring fields into the Mutlah estuary. The latter sponge, however, perishes as these ditches dry up, at an earlier period than that at which _S. alba_ reaches its maximum development.