Genus 243. Hexalastrum,[[282]] Haeckel, 1881, Prodromus, p. 461.
Definition.—Porodiscida 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 Discoidea. 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 with numerous short conical spines and one longer terminal spine. (Resembles Stauralastrum rhopalophorum, Pl. [45], fig. 1, but with six rays instead of four.)
Dimensions.—Radius of each arm 0.3, basal breadth 0.03, distal breadth 0.08.