Page:Scientific results HMS Challenger vol 18 part 1.djvu/730

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Definition.—Both opposite arms of similar size and form, with terminal spines.

3. Amphirrhopalum bigeminum, n. sp.

Both arms equal, in the proximal larger half simple, in the distal smaller half forked; each branch triangular, with a strong conical terminal spine. Axis of the branches straight. (Resembles Dicranastrum cornutum, Pl. 45, fig. 2, but without lateral arms.)

Dimensions.—Radius of the arms (without spines) 0.15, basal breadth 0.03; breadth of the bifurcation 0.08.

Habitat.—South Pacific, Station 284, surface.

4. Amphirrhopalum echinatum, n. sp. (Pl. 45, fig. 10).

Both arms equal, in the proximal smaller half simple, nearly square, in the distal larger half forked; the branches thorny, armed at the end with numerous spines, one larger on the terminal pole of the concavely curved arm-axis.

Dimensions.—Radius of the arms (without spines) 0.15, basal breadth 0.05; breadth of branches 0.03.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

Definition.—Both opposite arms of different size or form, without terminal spines.

5. Amphirrhopalum ypsilon, n. sp.

Both arms very different. Larger arm simple, egg-shaped, twice as long as broad; smaller arm in the basal half simple, nearly square, in the distal half forked; both branches egg-shaped, blunt. (Resembles Amphicraspedum wyvilleanum, Pl. 45, fig. 12, but wants the patagium.)

Dimensions.—Radius of the larger simple arm 0.18, breadth 0.09; radius of the smaller forked arm 0.15, breadth of its branches 0.05.

Habitat.—Indian Ocean, Madagascar, Rabbe, surface.

Definition.— with two chambered arms, opposite in one axis, connected by a lateral patagium; one arm or both forked at the distal end.

The genus Amphicraspedum exhibits the same bifurcation of the arms as does Amphirrhopalum, but differs from this ancestral form in the development of a patagium, an external connecticulum between the arms, which envelops the disk totally or partially.