Page:Scientific results HMS Challenger vol 18 part 1.djvu/722

514 prolongations of the four internal beams) alternating with four interradial spines arising from the margin of the disk.

Dimensions.—Diameter of the disk (with five rings) 0.13; breadth of each ring 0.014; pores 0.003.

Habitat.—Fossil in the rocks of Barbados.

Definition.— with numerous (five or more, commonly eight to twelve) solid radial spines, regularly or irregularly disposed on the margin of the circular or polygonal disk; margin of the disk surrounded by a thin, porous (but not chambered), equatorial girdle.

The genus Stylochlamydium is intermediate between Perichlamydium (with which it was formerly united) and Stylodictya. It deals with the former in the peculiar equatorial girdle, with the latter in the radial spines of the disk margin, which pierce the girdle. To both these genera it shows slow transitions, and can hardly be subjected to a sharp definition.

Definition.—All rings of the disk concentric, circular (or somewhat polygonal).

1. Stylochlamydium asteriscus, n. sp. (Pl. 41, fig. 10).

Perichlamydium asteriscus, Haeckel, 1879, MS.

All rings of the disk concentric, circular, or polygonal, with increasing breadth from the centre; the fifth ring twice as broad as the second. Pores irregular, roundish, three to four on the breadth of each ring; in the rings two to six times as large as in the equatorial girdle, which is half as broad or two-thirds as broad as the radius of the disk. Twelve bristle-shaped radial spines are connected by the girdle near to the points; four crossed spines arising from the central chamber; two others between these in each quadrant arising from the first ring.

Dimensions.—Diameter of the disk (with five rings) 0.15, with the girdle 0.25; breadth of the second ring 0.01, of the fifth ring 0.02; pores 0.001 to 0.005.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Stylochlamydium limbatum, Haeckel.

Perichlamydium limbatum, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 20.

Perichlamydium limbatum, Haeckel, 1862, Monogr. d. Radiol., p. 494.

All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, two on the breadth of each ring; twice to three times as large as the fine pores of the equatorial girdle, which is