Page:Scientific results HMS Challenger vol 18 part 1.djvu/356

148 radial spine, which at the distal end gives off three thread-like branches; by communication of these threads (at equal distances from the centre) the delicate outer medullary shell is formed. The polar spines very different; major spine six-sided pyramidal, longer than the diameter of the shell; minor pommel-shaped, shorter than the radius (similar to Xiphatractus glyptodon, Pl. 17, figs. 9, 10, but different in the double spherical cortical shell).

Dimensions.—Diameter of the four spheres—(A) 0.02, (B) 0.06, (C) 0.2, (D) 0.24; length of the major spine 0.3, of the minor 0.1.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Definition.— with five or more concentric, spherical lattice-shells.

Definition.— with five to six or more concentric lattice-shells and two free opposite spines of equal size and similar form.

The genus Caryostylus differs from its ancestral form, Stylocromyum, by the multiplication of the concentric spheres, the number of which amounts to five or six or more. I have only observed one single species of this genus. Some similar forms which in my Prodromus (1881, p. 454) were annexed to it, and disposed in three nearly allied genera (Caryoxiphus, Caryodoras, Caryolonche), have now been proved to belong to other groups, mainly ellipsoidal Druppulida.

1. Caryostylus hexalepas, n. sp.

Surface of the spherical shell smooth. Radial proportion of the component six concentric shells = 1 : 2 : 7 : 9 : 12 : 15. Both medullary shells connected only by six radial beams, opposite in pairs in the three dimensive axes. Between second and third shell numerous (twenty regularly disposed?) radial beams. Four cortical shells connected by very numerous (sixty to eighty or more?) short radial beams. Pores of all six shells regular, circular, the size increasing towards the surface, two to three times as broad as the bars. Two opposite polar spines very large, of equal size, three times as long as the shell radius, cylindrical, club-shaped at the thicker distal end. (The whole shell structure is similar to Pl. 15, fig. 2, but the shells are spherical, not ellipsoidal.)

Dimensions.—Diameter of the six spheres—(A) 0.02, (B) 0.04, (C) 0.15, (D) 0.18, (E) 0.24, (F) 0.3; length of the spines 0.5.

Habitat.—West Tropical Pacific, Station 225, depth 4475 fathoms.

Definition.— with spherical spongy shell (with or without enclosed latticed medullary shells).