Sponge hard but friable, forming sheets or patches often of great extent but never more than about 5 mm. thick; the surface minutely hispid, flat; colour pale yellow, the golden-yellow gemmules shining through the sponge in a very conspicuous manner; oscula inconspicuous; external membrane adherent; no basal chitinous membrane.
Skeleton dense but by no means strong; the reticulation close but produced mainly by single spicules, which form triangular meshes; radiating fibres never very distinct, only persisting for a short distance in a vertical direction; each gemmule enclosed in an open, irregular cage of skeleton-spicules.
Spicules. Skeleton-spicules short, slender, blunt, more or less regularly and strongly spiny, straight or feebly curved. No flesh-spicules. Gemmule-spicules with the rotulæ circular, very wide as compared with the shaft, concave on the surface, with the shaft projecting as an umbo on the surface; the lower rotula often a little larger than the upper.
Gemmules numerous, situated at the base of the sponge in irregular, one-layered patches, small (0.32 × 0.264 mm.), of a brilliant golden colour, distinctly wider than high, with a single aperture situated on an eminence on the apex, each clothed (when mature) with a pneumatic coat that contains relatively large but irregular air-spaces among which the spicules stand with the rotulæ overlapping alternately, a funnel-shaped pit in the coat descending from the surface to the upper rotula of each of them; the surface of the gemmule covered with irregular projections.
| Diameter of gemmule | 0.32 × 0.264 mm. |
| Length of skeleton-spicule | 0.177 mm. |
| Length of gemmule-spicule | 0.015 mm. |
| Diameter of rotule | 0.022 mm. |
This species appears to be related to T. pennsylvanica, from which it differs mainly in the form of its gemmule-spicules and the structure of its gemmule. My original description was based on specimens in which the gemmule-spicules were not quite mature.
Type in the Indian Museum.
Geographical Distribution.—Lower Bengal and Lower Burma. Localities:—Bengal, Calcutta (Annandale): Burma, jungle pool near Kawkareik, Amherst district, Tenasserim (Annandale).
Biology.—This species covers a brick wall at the edge of the Museum tank in Calcutta every year during the "rains." In the cold weather the wall is left dry, but it is usually submerged to a depth of several feet before the middle of July. It is then rapidly covered by a thin layer of the sponge, which dies down as soon as the water begins to sink when the "rains" are over. For some months the gemmules adhere to the wall on account of the cage of spicules in which each of them is enclosed, but long before the water rises again the cages disintegrate and the gemmules are set free. Many of them fall or are carried by the wind into the water, on the surface of which, owing to their thick pneumatic coat, they float buoyantly. Others are lodged in cavities in the wall. On the water the force of gravity attracts them to one another and to the edge of the pond, and as the water rises they are carried against the wall and germinate. In thick jungle at the base of the Dawna Hills near Kawkareik[[AI]] in the interior of Tenasserim, I found the leaves of shrubs which grew round a small pool, covered with little dry patches of the sponge, which had evidently grown upon them when the bushes were submerged. This was in March, during an unusually severe drought.