Page:Scientific results HMS Challenger vol 18 part 1.djvu/294

86

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

The genus Caryosphæra, the only observed form of this subfamily, comprises those in which the shell is composed of two medullary and three or more cortical shells. Such forms (without radial spines) are very rare; I observed only two species, one with five, the other with six shells. They are derived from Cromyosphæra by further apposition of outer cortical shells.

1. Caryosphæra pentalepas, n. sp.

Shell composed of five concentric spheres, with radial proportion = 1 : 2 : 8 : 10 : 12. Both medullary shells with regular circular pores, twice as broad as the bars. First cortical shell with regular, circular, hexagonally framed pores, three times as broad as the bars; second cortical shell with regular hexagonal pores, four times as broad as the bars; third (outermost) cortical shell with regular hexagonal pores and very thin thread-like bars. Surface smooth.

Dimensions.—Diameter of the five shells—(A) 0.02, (B) 0.04, (C) 0.16, (D) 0.2, (E) 0.24.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

2. Caryosphæra hexalepas, n. sp.

Shell composed of six concentric spheres, with the radial proportion = 1 : 2 : 4 : 5 : 6 : 8. All six shells with regular circular pores, two to four times as broad as the bars, with increasing size from the centrum against the smooth surface.

Dimensions.—Diameter of the six shells—(A) 0.025, (B) 0.05, (C) 0.1, (D) 0.13, (E) 0.16, (F) 0.2.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms; also fossil in Barbados.

Definition.— with spongy spherical shell, with or without latticed medullary shell in the centre.

Definition.— forming a solid sphere of spongy framework, without enclosed medullary shell, and without central cavity.