Habitat.—North Pacific, Station 241, surface.
Genus 80. Hexadendron,[[111]] Haeckel, 1881, Prodromus, p. 452.
Definition.—Cubosphærida with three concentric lattice-spheres and six branched spines of equal size.
The genus Hexadendron differs from Hexacontium in the ramification of the six dimensive spines, and from the similar Hexancistra in the duplication of the medullary shell. As in the latter instance, each spine can bear either three simple lateral branches or three rows of pinnate lateral branches.
1. Hexadendron quadricuspis, n. sp.
All three shells spherical, with radial proportion = 1 : 2 : 6. Pores of both medullary shells regular circular, twice as broad as the bars. Pores of the cortical shell irregular roundish, four to six times as broad as the bars; surface a little thorny. Six radial spines prismatic, with three prominent wing-like edges, which are prolonged below the distal end in three curved lateral branches. (Differs from Hexalonche quadricuspis, Pl. [22], fig. 11, mainly in the double medullary shell.)
Dimensions.—Diameter of the outer shell 0.15, middle 0.05, inner 0.025; length of the spines 0.12, breadth 0.01.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
2. Hexadendron bipinnatum, n. sp. (Pl. [23], fig. 1).
All three shells regular octahedral, with very delicate network of irregular polygonal meshes, and very thin, thread-like bars between them; their radial proportion = 1 : 2.5 : 7.5. Surface of the cortical shell covered with numerous bristle-shaped by-spines, as long as the radius. Six main spines very large, three-sided prismatic, with three rows of pinnate, lateral branches, on the three wing-like, spirally twisted edges (similar to those of Hexancistra mirabilis, p. [189], Pl. [23], fig. 3).