Page:Scientific results HMS Challenger vol 18 part 1.djvu/371

Rh Dimensions.—Diameter of the cortical shell 0.12, medullary shell 0.025; pores of the former 0.03, bars 0.004; length of the major spines 0.12, minor 0.03.

Habitat.—Fossil in Barbados.

Definition.— with two concentric lattice-spheres and four crossed simple spines, one of which is much larger than the other three.

The genus Stauroxiphos differs from its ancestral form, Staurolonche, in the greater development of one single spine, and exhibits therefore the same relation to it that Stylostaurus bears to Staurosphæra.

1. Stauroxiphos gladius, n. sp. (Pl. 15, fig. 7).

Cortical shell thick walled, smooth, three times as broad as the medullary shell. Pores of the outer shell regular, circular, regularly six-lobed on the outer opening, four times as broad as the bars; about six on the quadrant. Pores of the inner shell only one-third as large, simple, circular. Three of the four radial spines of nearly equal size, pommel-shaped, with three prominent, dentated wings, somewhat shorter than the shell radius and about half as broad as long; the fourth spine much larger, sword-like, about three times as long as the shell radius.

Dimensions.—Diameter of the outer shell 0.12, of the inner 0.04; pores of the former 0.01, bars 0.0025; pores of the latter 0.003, bars 0.001; length of the major spine 0.18, of the three minor 0.04.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

Definition.— with three concentric spherical lattice-shells.

Definition.— with three concentric lattice-spheres and four crossed, equal, simple spines.

The genus Stauracontium differs from its probable ancestral form, Staurolonche, in the duplication of the cortical shell.

Definition.—Pores of the cortical shell regular, all of nearly equal size and similar form; surface smooth.