Page:Scientific results HMS Challenger vol 18 part 1.djvu/341

Rh Dimensions.—Diameter of the sphere 0.08, pores 0.006, bars 0.003; diameter of the circular ring 0.16; length of the radial spines 0.02 to 0.04; thickness of the ring and the axial beams 0.01.

Habitat.—Fossil in the Barbados rocks.

6. Saturnalis rotula, n. sp. (Pl. 13, fig. 15).

Pores of the spherical shell regular, circular, twice as broad as the bars; sixteen to twenty on the half equator. Ring circular, armed with fifteen to twenty strong, conical, irregular spines, partly simple, partly divided into two or three irregular branches; diameter of the ring two and a half times as great as that of the sphere.

Dimensions.—Diameter of the sphere 0.08, pores 0.004, bars 0.002; diameter of the circular ring 0.2, length of its spines 0.02 to 0.03; thickness of the ring and the radial beams 0.01.

Habitat.—North Pacific, Station 244, surface.

Definition.— with two concentric, spherical lattice-shells.

Definition.— with two concentric lattice-spheres and two free spines of equal size and similar form.

The genus Stylosphæra, the most simple form of the Sphærostylida, can be derived either from Xiphosphæra by duplication of the spherical shell, or from Carposphæra by development of two opposite polar spines. The inner or medullary shell is enclosed in the central capsule, whilst the outer or cortical shell lies outside it; the two are connected by two or more radial beams, piercing the wall of the capsule.

Definition.—Pores of the cortical shell regular, of nearly equal size and similar form; surface smooth or a little rough, without spines or thorns.

1. Stylosphæra musa, n. sp.

Radial proportion of the two concentric spheres = 3 : 1. Cortical shell thin walled, smooth, with regular, hexagonal pores, three times as broad as the thin bars; twelve on the half equator. Polar spines three-sided pyramidal, as long as the axis of the cortical shell, one-tenth as broad at the base.

Dimensions.—Diameter of the outer shell 0.2, pores 0.01, bars 0.003; diameter of the inner shell 0.06; length of the polar spines 0.2, basal breadth 0.02.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.