Page:Scientific results HMS Challenger vol 18 part 1.djvu/1087

Rh Dimensions.—Diameter of the shell 0.13; length of the six marginal spines 0.12, basal breadth 0.04.

Habitat.—Tropical Atlantic, Station 348, surface.

2. Hexonaspis hexapleura, n. sp. (Pl. 140, fig. 15).

All six hydrotomical spines of nearly equal size, triangular, compressed, six-edged, about as long as the radius of the shell and twice as long as broad on the base. Two strong prominent ribs on each flat side of the spines. Shell very thick-walled, with a very small cavity.

Dimensions.—Diameter of the shell 0.11; length of the six marginal spines 0.06, basal breadth 0.03.

Habitat.—South Atlantic, Station 332, surface.

3. Hexonaspis hexagona, n. sp.

All six hydrotomical spines of equal size, very short, triangular, only half as long as broad at the base. The whole shell accordingly forms a regular hexagon, the six corners of which are formed by the distal points of the rudimentary spines, the six sides by their straight lateral edges. Shell very dark.

Dimensions.—Diameter of the shell 0.2; length of the six marginal spines 0.03, basal breadth 0.06.

Habitat.—South Atlantic (east of Patagonia), Station 318, surface.

Definition.—Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

4. Hexonaspis hastata, n. sp. (Pl. 140, fig. 16).

Six hydrotomical spines of unequal size; two larger equatorial spines with six prominent wings, about as long as the radius of the shell and half as broad at the base; the four polar spines quite as broad, but only half as long, nearly equilateral triangular, with two shallow furrows on each flat side at the broader base. The fourteen smaller spines not visible on the surface, quite rudimentary. Crests of the surface elegantly denticulated.

Dimensions.—Diameter of the shell 0.14; length of the two equatorial spines 0.08, of the four polar spines 0.04; basal breadth 0.04.

Habitat.—Central Pacific, Station 271, surface.