Page:Scientific results HMS Challenger vol 18 part 1.djvu/622

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Definition.— with three radial spines on the margin of the disk, placed in its equatorial plane.

The genus Theodiscus is the most simple form of those very numerous in which three rays are developed on the margin of the disk; a symbol of the Christian dogma of the Trinity. Commonly the three angles between the three spines are equal, more rarely one angle is larger than the two others which are equal. The shell of some species is nearly spherical (formerly separated by me as Theosphæra), whilst in others it is a flattened biconvex lens.

Definition.—Angles between the three radial spines equal (triangle equilateral).

1. Theodiscus divinus, n. sp.

Disk nearly spherical, with smooth surface. Pores regular, circular, hexagonally framed; seven to eight on the radius. Three angles between the spines equal. Spines prismatic, straight, twice as broad as one pore, eight to eleven times as long as the shell diameter.

Dimensions.—Diameter of the disk 0.1, of the pores 0.006; length of the spines 0.8 to 1.1, breadth 0.01.

Habitat.—Central Pacific, Station 265, surface.

2. Theodiscus christianus, n. sp.

Disk nearly spherical, with smooth surface. Pores regular, circular, prolonged into short cylindrical, prominent tubuli, half as high as broad; eight to nine on the radius. Three angles between the spines equal. Spines prismatic, straight, twice as broad as one pore, twelve to fifteen times as long as the shell diameter.

Dimensions.—Diameter of the disk 0.08, of the pores 0.005; length of the spines 1.1 to 1.2, breadth 0.01.

Habitat.—Central Pacific, Station 271, surface.

3. Theodiscus trinitatis, n. sp.

Disk a rather flattened, biconvex lens, about twice as broad as thick. Pores regular, circular, not prolonged into tubuli; five to six on the radius. Three angles between the spines equal. Spines pyramidal, three times as broad as one pore, about twice as long as the shell diameter.