Definition.—Cubosphærida with five to six or more concentric lattice-shells and six branched spines of equal size.
The genus Hexacaryum is distinguished from the foregoing Cubosphæra by ramification of the six radial spines, and therefore exhibits the same relation to it that Hexancistra bears to Hexastylus, &c.
1. Hexacaryum arborescens, n. sp. (Pl. [23], figs. 4, 4a).
Shell composed of five, six, or more concentric shells, which are united by six very large radial spines. The two medullary shells spherical, inner with regular, circular, outer with irregular polygonal pores. All cortical shells (third and following) not spherical, but regular octahedral, with irregular polygonal meshes and thin bars. Radial spines prismatic, with three wing-like, spirally twisted edges, which at equal distances send out thin forked lateral branches (six on each verticil); by further ramification and communication of these branches the triangular net-plates arise, filling out the sides of the octahedral cortical shells. Diameter of all shells little different. The outer free parts of the six spines are arborescent, twice to three times as long as the enclosed inner parts, and bear six to eight verticils of free lateral branches, decreasing in size towards the distal end (similar to Arachnosphæra).
Dimensions.—Diameter of the six shells—(A) 0.015, (B) 0.04, (C) 0.1, (D) 0.16, (E) 0.22, (F) &c.; average distance of the concentric octahedra = 0.06; length of the radial spines 0.3 to 0.4 and more, breadth 0.02.
Habitat.—Central Pacific, Station 274, surface.
Subfamily Hexadorida,[[118]] Haeckel, 1881, Prodromus, pp. 449, 455.
Definition.—Cubosphærida with spongy spherical or octahedral shell (with or without enclosed concentrical lattice-shells).
Genus 85. Cubaxonium,[[119]] n. gen.
Definition.—Cubosphærida with solid spongy spherical or octahedral shell, without latticed medullary shell in the centre, and with six simple radial spines of equal size.