Page:Scientific results HMS Challenger vol 18 part 1.djvu/355

Rh The genus Stylocromyum differs from its probable ancestral form, Amphisphæra, by the duplication of the cortical shell; two opposite radial beams, piercing the wall of the central capsule, connect it with the double medullary shell, and are prolonged outside into two equal spines.

1. Stylocromyum amphiconus, n. sp.

Surface of the shell smooth. Radial proportion of the four spheres = 1 : 2 : 8 : 9. Two medullary shells inside the central capsule, two cortical shells outside it. Interval between the second and third shells the greatest. Pores of all the shells regular, circular, two to four times as broad as the bars. Both polar spines equal, conical, about as long as the axis of the outermost sphere, as broad at the base as the innermost.

Dimensions.—Diameter of the four spheres—(A) inner medullary shell 0.03, (B) outer medullary shell 0.06, (C) inner cortical shell 0.25, (D) outer cortical shell 0.28; length of the polar spines 0.3, basal breadth 0.03.

Habitat.—Central Pacific, Station 273, depth 2350 fathoms.

2. Stylocromyum amphipyramis, n. sp.

Surface of the shell smooth. Radial proportion of the four spheres = 2 : 3 : 6 : 8. Both medullary shells with regular, circular pores, twice as broad as the bars. Both cortical shells with irregular, roundish, much larger pores, three to six times as broad as the bars. Both polar spines equal or nearly equal, three-sided pyramidal, about as long as the axis of the third shell.

Dimensions.—Diameter of the four spheres—(A) 0.04, (B) 0.06, (C) 0.12, (D) 0.16; length of the polar spines 0.11, basal breadth 0.02.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

Definition.— with four concentric lattice-spheres and two free spines of different size or form.

The genus Cromyostylus differs from its ancestral form, Stylocromyum, in the differentiation of the two unequal polar spines.

1. Cromyostylus gladius, n. sp.

Surface of the shell smooth. Radial proportion of the four spheres = 1 : 3 : 10 : 12. Both medullary shells with regular, circular, simple pores. Inner cortical shell with regular, circular, hexagonally framed pores, twice as broad as the bars. From each hexagon-corner arises a