Page:Scientific results HMS Challenger vol 18 part 1.djvu/767

Rh 2. Pentophiastrum caudatum, n. sp. (Pl. 47, fig. 5).

Arms in pairs different; four arms in the basal half simple, in the distal half forked; the fifth (posterior) odd arm simple, undivided, cylindrical; the anterior pair a little smaller than the posterior; the neighboring branches of the two pairs on each side larger than the two others. Axes of the arms and their branches straight.

Dimensions.—Radius of the arms about 0.5, breadth 0.12.

Habitat.—North Atlantic, Station 353, depth 2965 fathoms.

3. Pentophiastrum forcipatum, n. sp. (Pl. 47, fig. 4).

Arms in pairs different, all in the basal two thirds simple, in the distal third forked. Only in the posterior (odd) arm both branches are equal, in the four others unequal. The common axis of the posterior lateral pair is horizontal, perpendicular to the median line; the axes of the anterior pair are pincer-like, concavely curved towards the median line or principal axis.

Dimensions.—Radius of the arms about 0.5, breadth 0.14.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Definition.— with six simple chambered arms, without a patagium.

The genus Hexalastrum, together with the following Hexinastrum, encloses those Euchitonida in which the number of the chambered arms surrounding the central disk amounts to six. This is the highest number of these articulated marginal appendages which is reached in any. Formerly (1881) in my Prodromus, p. 459, I supposed that the same number was reached also by one Coccodiscid, and called this genus Hexactura. Afterwards I was convinced that this form was also a Hexalastrum.

1. Hexalastrum palmanthum, n. sp.

All six arms equal, with equal angles between them. Each arm club-shaped, three times as long as broad, twice as broad at the thickened distal end as at the base, without a terminal spine.

Dimensions.—Radius of each arm 0.2, basal breadth 0.02, distal breadth 0.06.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

2. Hexalastrum crinanthum, n. sp.

All six arms equal, with equal angles between them. Each arm club-shaped, four times as long as broad, at the egg-shaped distal end three times as broad as in the linear basal part, provided