Page:Scientific results HMS Challenger vol 18 part 1.djvu/350

142 4. Saturnulus planetes, n. sp. (Pl. 16, fig. 17).

Cortical shell smooth, twice as broad as the medullary shell, with regular, circular pores, of the same breadth as the bars; sixteen to eighteen on the half equator. Ring elliptical, smooth, with strong prominent edges, constricted at the poles of the minor axis, its major diameter three times as great as that of the outer sphere.

Dimensions.—Diameter of the outer sphere 0.08, pores and bars 0.005; inner sphere 0.035; major axis of the ring 0.25, minor axis 0.2; thickness of the ring and the axial beams 0.012.

Habitat.—Indian Ocean, Sunda Strait, Rabbe; Station 200, surface.

Definition.— with three concentric spherical lattice-shells.

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

The genus Amphisphæra differs from its probable ancestral form, Stylosphæra, in the triple spherical lattice-shell. Commonly two of these lie within the central capsule (medullary shell), whilst the third lies outside it (cortical shell). But sometimes this order is inverted, the cortical shell being double, the medullary shell simple; and perhaps these forms may better represent a peculiar genus, Amphisphæridium.

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. Amphisphæra neptunus, n. sp.

Radial proportion of the three concentric spheres = 4 : 2 : 1. Cortical shell thick walled, smooth, with regular, circular, hexagonally framed pores, of the same breadth as the bars; twelve to fifteen on the half equator. Polar spines three-sided pyramidal, with strong prominent edges, about as long as the radius of the outer shell, half as broad at the base. (Similar to Stylatractus neptunus, Pl. 17, fig. 6, but differs in the purely spherical form of the three concentric shells and the regular form of the network and of the polar spines.)

Dimensions.—Diameter of the outer shell 0.16, middle shell 0.08, inner shell 0.04; pores and bars of the cortical shell 0.008; length of the polar spines 0.08, basal breadth 0.04.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.