Page:Scientific results HMS Challenger vol 18 part 1.djvu/375

Rh The genus Cromyostaurus differs from the preceding Staurocromyum, its ancestral form, in the ramification of the four crossed spines.

1. Cromyostaurus verticillatus, n. sp.

Radial proportion of the four spheres = 1 : 3 : 11 : 13. Both medullary shells with small, regular, circular pores; inner cortical shell with regular, hexagonal pores; from the hexagon-corners arise small, radial by-spines, which at equal distances from the centre send out forked tangential branches, three from each spine, and by communication of these form the outer, delicate, cortical shell. Four main spines nearly as long as the shell diameter, three-sided prismatic, with four to six verticils of ramified lateral branches, each verticil composed of three forked branches, which ramify again.

Dimensions.—Diameter of the four shells—(A) 0.26, (B) 0.22, (C) 0.06, (D) 0.02; length of the spines 0.24.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

Definition.— with five or more concentric spherical lattice-shells.

Definition.— with five or more concentric lattice-spheres and four crossed, equal spines.

The genus Staurocaryum has arisen from the preceding Staurocromyum by the further multiplication of the concentric spheres; in the only observed form there are six, at nearly equal distances apart.

1. Staurocaryum arborescens, n. sp. (Pl. 15, fig. 8).

Shell composed of six concentric latticed spheres, at nearly equal distances apart, and with somewhat regular, circular pores, the size of which gradually increases from the first to the sixth shell. The surface of the outermost shell is densely covered with numerous arborescent by-spines, which bifurcate from three to four times, and are three-sided pyramidal at the base, and twice as long as the distance between each two shells. The six shells are connected only by four crossed, conical, radial beams, which increase in diameter from the centre, and are prolonged outside into very stout cylindrical, radial spines, irregularly covered with small thorns and forked ramules, and nearly as long as the shell diameter. Only a single specimen was observed.