Page:Scientific results HMS Challenger vol 18 part 1.djvu/623

Rh Dimensions.—Diameter of the disk 0.06, of the pores 0.007; length of the spine 0.12, basal breadth 0.02.

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

Definition.—Angles between the three radial spines unequal, two paired angles equal, larger or smaller than the odd angle (triangle isosceles).

4. Theodiscus vanitatis, n. sp.

Disk nearly spherical, with smooth surface. Pores irregular, roundish; eight to ten on the radius. Three angles between the spines unequal; one odd angle larger than both others. Spines pyramidal, of unequal size; one odd spine larger, both others smaller than the shell diameter.

Dimensions.—Diameter of the disk 0.12, pores 0.004 to 0.006; length of the odd spine 0.2, of the paired spines 0.1.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms.

5. Theodiscus nirvana, n. sp.

Disk a flat biconvex lens, about twice as broad as thick. Pores regular, circular; ten to twelve on the radius. Three angles between the spines unequal; one odd angle smaller than both others. Spines prismatic, very long and thin, twice as broad as one pore, ten to twelve times as long as the shell diameter.

Dimensions.—Diameter of the disk 0.1, pores 0.005; length of the spines 1 to 1.2 or more, breadth 0.01.

Habitat.—Indian Ocean, Ceylon, surface, Haeckel.

Definition.— with four radial spines on the margin of the disk, crossed in the equatorial plane.

The genus Crucidiscus is the most simple form of the Staurodiscida, or of the numerous (belonging to different families) in which the margin of the disk bears four radial spines, lying in the equatorial plane, and crossed at right angles. Whilst commonly the internal shell-cavity of Crucidiscus is quite simple, in one case it bears four centripetal axial rods, as inner prolongations of the outer radial cross-spines, perhaps indications of a lost medullary shell (comp. p. 410).