Type in the Amsterdam Museum; a co-type in Calcutta.
Perhaps the Japanese form, which has spindle-shaped gemmule-spicules with comparatively short and regular spines, should be regarded as a third subspecies, and the Siberian form as a fourth.
10. Spongilla gemina*, sp. nov.
Sponge forming small, shallow, slightly dome-shaped patches of a more or less circular or oval outline, minutely hispid on the surface, friable but moderately hard. Oscula numerous but minute and inconspicuous, never star-shaped. Dermal membrane adhering closely to the sponge. Colour grey or brown.
Skeleton forming a close and regular network at the base of the sponge, becoming rather more diffuse towards the external surface; the radiating and the transverse fibres both well developed, of almost equal diameter. Little spongin present.
Spicules. Skeleton-spicules slender, smooth, sharply pointed. No flesh-spicules. Gemmule-spicules long, slender, cylindrical, blunt or bluntly pointed, somewhat irregularly covered with minute straight spines.
Gemmules small, bound together in pairs, as a rule free in the parenchyma but sometimes lightly attached at the base of the sponge. Each gemmule flattened on the surface by which it is attached to its twin, covered with a thin coat of polygonal air-spaces which contains two layers of gemmule-spicules crossing one another irregularly in a horizontal plane. One or two foraminal tubules present on the surface opposite the flat one, bending towards the latter, often of considerable length, cylindrical and moderately stout.
Type in the Indian Museum.
This species is closely allied to S. fragilis, from which it may be distinguished by the curious twinned arrangement of its gemmules. It also differs from S. fragilis in having extremely small and inconspicuous oscula.
Locality. I only know this sponge from the neighbourhood of Bangalore, where Dr. Morris Travers and I found it in October, 1910 growing on stones and on the leaves of branches that dipped into the water at the edge of a large tank.