Page:Scientific results HMS Challenger vol 18 part 2.djvu/40

916 3. Hexaplagia collaris, n. sp.

Spines in opposite pairs in three diameters, crossed in the common centre, straight, cylindrical, pinnate, with three to four pairs of opposite lateral branches or regular pinnulæ. All six spines are equidistant, of equal size and similar form, and lie with their branches nearly in one horizontal plane. Therefore they are similar to the six radial rods in the collar septum of many and  (e.g., Calpophæna, Pl. 53, fig. 18).

Dimensions.—Length of all six spines 0.18, of their basal pinnulæ 0.04.

Habitat.—East of New Zealand, Station 169, surface.

4. Hexaplagia australis, n. sp.

Spines unequal, at unequal intervals, not opposite in pairs, cylindrical, irregularly branched and curved. In this species a definite arrangement of the six different spines could not be detected.

Dimensions.—Length of the spines 0.2 to 0.3, of their largest branches 0.1.

Habitat.—South of Australia, Station 160, surface.

Definition.— with six radial spines, arising in two opposite divergent groups from the two poles of a common central rod.

The genus Plagonium differs from the preceding closely allied Hexaplagia in the remarkable peculiarity, that the six radial spines do not arise from one common central point, but from the two poles of a common horizontal middle rod; three divergent spines on each pole. The skeleton of Plagonium exhibits therefore the same remarkable form which is found in the isolated spicula of numerous (e.g., Lampoxanthium punctatum, Sphærozoum punctatum), and bears the same relation to Hexaplagia that Plagonidium does to Tetraplagia.

1. Plagonium sphærozoum, n. sp. (Pl. 91, fig. 6).

Spines straight and stout, three-sided prismatic, about twice as long as the common middle rod, irregularly branched or nearly verticillate, with short thorny branches. Similar to the single spicula of some species of Sphærozoum and Lampoxanthium.

Dimensions.—Length of the spines 0.12, of the middle rod 0.06.

Habitat.—Equatorial Atlantic, Station 347, surface.