Geographical Distribution.—The genus includes so large a proportion of small, inconspicuous species that its distribution is probably known but imperfectly. It would seem to have its headquarters in N. America but also occurs in Europe and Asia. In India three species have been found, one of which (T. pennsylvanica) has an extraordinarily wide and apparently discontinuous range, being common in N. America, and having been found in the west of Ireland, the Inner Hebrides, and near the west coast of S. India. The other two Indian species are apparently of not uncommon occurrence in eastern India and Burma.
Key to the Indian Species of Trochospongilla.
| I. | Rotules of thegemmule-spicules equal or nearly so. | |
| A. | Skeleton-spiculessmooth, usually pointed | latouchiana,p. [115]. |
| B. | Skeleton-spiculesspiny, blunt | phillottiana, p. [117]. |
| II. | Upper rotule of thegemmule-spicules distinctly smaller than the lower. | |
| Skeleton-spicules spiny, pointed | pennsylvanica, p. [118]. |
18. Trochospongilla latouchiana*, Annandale.
Trochospongilla latouchiana, Annandale, J. Asiat. Soc. Bengal, 1907, p. 21, fig. 5. Trochospongilla latouchiana, id., Rec. Ind. Mus. ii, p. 157 (1908). Trochospongilla leidyi, id. (nec Bowerbank), ibid. iii, p. 103 (1909).
Fig. 24.—Trochospongilla latouchiana.
Vertical section of part of skeleton with gemmules in situ, × 30; also a single gemmule, × 70. (From Calcutta).
Sponge forming cushion-shaped masses rarely more than a few centimetres in diameter or thickness and of a brown or yellow colour, hard but rather brittle; surface evenly rounded, minutely hispid; oscula inconspicuous, small, circular, depressed, very few in number; external membrane adhering closely to the parenchyma; a chitinous membrane at the base of the sponge. Larger sponges divided into several layers by similar membranes.
Skeleton dense, forming a close reticulation; radiating fibres slender but quite distinct, running up right through the sponge, crossed at frequent intervals by single spicules or groups of spicules.