Page:Scientific results HMS Challenger vol 18 part 1.djvu/306

98

Definition.— with simple shells, on the inside with radial centripetal beams.

The genus Tribonosphæra differs from Collosphæra by a very peculiar and rare character, the development of centripetal radial sticks on the internal face of the shell; these beams are not united in the centrum, but finish freely in a certain distance from it.

1. Tribonosphæra centripetalis, n. sp. (Pl. 5, fig. 12).

Shell roundish or subspherical, with numerous small circular or roundish pores, about twice as broad as the bars. Twenty to thirty pores on the half meridian of the shell. Outside of the shell smooth, inside a variable number (ten to twenty) of thin, radial, centripetal sticks or spines, one-third or one-half as long as the radius of the shell. (In the central capsule many very large crystals, resting after the destruction of the capsule.)

Dimensions.—Diameter of the shell 0.1 to 0.12, of the pores 0.003 to 0.005, of the bridges 0.001 to 0.002; length of the inner centripetal sticks 0.02 to 0.03.

Habitat.—Central Pacific, Station 271, surface.

Definition.— with simple shells, having on the inside radial centripetal tubes, the walls of which are solid.

The genus Pharyngosphæra differs from Collosphæra by the development of radial tubules on the inside of the shell, which are directed centripetally towards its centre. The wall of the tubule is solid, not latticed as in the following genus.

1. Pharyngosphæra stomodæa, n. sp. (Pl. 5, fig. 10).

Shell irregular polyhedral, with ten to fifteen polygonal faces and rounded edges. Pores very small, circular, irregularly scattered, smaller than the bars. Twelve to fifteen pores on the half meridian of the shell. On the inside of every shell-face one short, nearly cylindrical, centripetal tubule, twice as long as broad, and about one-third as long as the shell radius. Outer umbilical mouth of the tubules somewhat wider than the inner truncated mouth.

Dimensions.—Diameter of the shell 0.11 to 0.12, of the pores 0.003 to 0.005, of the bars 0.01 to 0.02; length of the inner tubuli 0.02, breadth of them 0.01.

Habitat.—South Pacific, Station 288, depth 2600 fathoms.