Page:Scientific results HMS Challenger vol 18 part 1.djvu/292

84 outer pores, like the five petals of a flower. Medullary shell half as broad as the inner cortical shell, with regular circular pores.

Dimensions.—Diameter of the outer shell 0.25, middle 0.2, inner 0.1; outer pores on an average 0.006, middle 0.012, inner 0.004.

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

Definition.— with four concentric spherical latticed shells, united by radial beams.

Definition.— with two intracapsular (medullary) shells and two extracapsular (cortical) shells; the former united with the latter by radial beams piercing the wall of the central capsule.

The genus Cromyosphæra is the only known genus of Cromyosphærida, or of such, the smooth shell of which is composed of two medullary and two cortical shells. There may possibly be other Cromyosphærida, in which the shell is composed of one simple medullary and three cortical shells, or only of four extra-capsular cortical shells; but such have not as yet been observed. Caryosphæra polysphærica, Bütschli, 1882 (L. N. 41, Taf. xxiii. fig. 12) is probably a Cromyosphæra (fossil in Barbados).

1. Cromyosphæra quadruplex, n. sp. (Pl. 30, fig. 9).

Radial proportion of the four spheres = 1 : 2 : 4 : 5. Outer cortical shell smooth, with large regular hexagonal pores, ten times as broad as the bars; inner cortical shell with irregular polygonal pores, five times as broad as the bars. Both medullary shells with regular circular pores of the same breadth as the bars.

Dimensions.—Diameter of the four spheres—(A) 0.16, (B) 0.12, (C) 0.06, (D) 0.03.

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

2. Cromyosphæra rosetta, n. sp.

Radial proportion of the four spheres = 1 : 2 : 8 : 10. Outer cortical shell smooth, with regular hexagonal pores and very thin bars; inner cortical shell with the same number of exactly corresponding, regular circular, hexagonally framed pores, twice as broad as the bars; the corners of the outer and inner hexagons united by radial bristles. Both medullary shells with regular circular pores, twice as broad as the bars.

Dimensions.—Diameter of the four spheres—(A) 0.2, (B) 0.16, (C) 0.04, (D) 0.02.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.