Page:Scientific results HMS Challenger vol 18 part 1.djvu/765

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Definition.—Arms of different sizes, one odd arm larger than the two others; the opposite odd angle generally different from the four other angles.

3. Pentalastrum ophidiaster, n. sp. (Pl. 44, fig. 3).

Arms nearly triangular, at their obtuse truncated distal end twice as broad as at their base. Four arms equal, with five joints each; the fifth arm twice as long, with seven joints. Angles between the arms nearly equal; the odd angle a little larger.

Dimensions.—Radius of the larger odd arm 0.25, of the four smaller arms 0.15; basal breadth 0.035, distal breadth 0.07.

Habitat.—Pacific, central area, Station 274, surface.

4. Pentalastrum cometa, n. sp.

Arms nearly cylindrical, at their obtuse truncated distal end one and a half times as broad as at their base. Posterior odd arm very large, with eleven joints, about three times as long as the two lateral arms (with five joints each) and four times as long as the two anterior arms (with three joints each). Angles between the paired arms different; the two lateral angles smaller than the two posterior, and these smaller than the odd anterior angle.

Dimensions.—Radius of the odd posterior arm 0.5, of the lateral arms 0.25, of the anterior arms 0.18; basal breadth 0.05, distal breadth 0.08.

Habitat.—South Pacific, Station 288, surface.

Definition.— with five simple, undivided, chambered arms, connected by a patagium.

The genus Pentinastrum differs from the foregoing Pentalastrum only in the development of a patagium or connecticulum between the arms, and bears therefore the same relation to it that Histiastrum does to Stauralastrum, or Hymeniastrum to Dictyastrum.

1. Pentinastrum asteriscus, n. sp. (Pl. 44, fig. 2).

All arms equal, twice as long as broad, at their base two-thirds as broad as at their truncated distal end, which bears a strong, pyramidal, terminal spine. Each arm is divided by five transverse septa into six joints or chambers, and each of these by a radial beam into a pair of chambers. The five radial beams arise from the innermost chamber of the central disk, and end in the five terminal