Subgenus 1. Spongastrella, Haeckel.
Definition.—Cross formed by the four arms regular, rectangular, with the arms of equal size and equidistant.
1. Spongaster tetras, Ehrenberg.
Arms at equal distances, forming a rectangular, regular Myelastrum, papiliocross, club-shaped, about twice as long as the diameter of the square central disk and eight times as long as broad at their base. Distal ends rounded, perfectly enclosed by the complete patagium, which forms a regular square, with slightly concave sides.
Dimensions.—Radius of the arms 0.12, distal breadth 0.03, basal breadth 0.015; length of the square side 0.2.
Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface and in various depths.
2. Spongaster quadratus, n. sp.
Arms at equal distances, forming a regular, rectangular cross, club-shaped, about four times as long as the diameter of the central circular disk, and five times as long as broad at the base. Basal third of the arms square; distal two thirds triangular, three times as broad, with a truncated distal end. Patagium complete, perfectly enveloping the arms, and bordered by an elegant, radially striated, broad edge, forming a regular square. (Similar to Histiastrum quadratum, Pl. 46, fig. 4, but quite spongy.)
Dimensions.—Radius of the arms 0.15, distal breadth 0.06, basal breadth 0.02; length of the square side 0.25.
Habitat.—Pacific, central area, Stations 270 to 274, depths 2350 to 2925 fathoms.
3. Spongaster cruciatus, n. sp.
Arms at equal distances, forming a rectangular, regular cross, lanceolate, three times as long as broad and as the diameter of the central circular disk. Ends of the arms provided with a short conical spine. Patagium incomplete, enveloping only the basal half of the arms, forming a regular square with concave sides.
Dimensions.—Radius of the arms 0.18, greatest breadth 0.05; length of the square side 0.2.
Habitat.—South Pacific, Station 288, surface.
