Page:Scientific results HMS Challenger vol 18 part 2.djvu/37

Rh 3. Plagoniscus cortinaris, n. sp.

Spines three-sided prismatic, straight, verticillate. Apical spine with twelve verticils, one and a half times as long as the three basal spines, each of which bears eight verticils of three branches. The branches are also prismatic, straight, on each edge parallel, tapering towards the apex, in the three basal spines forked, in the apical spine more branched. Similar to the cortinar skeleton of Clathrocorys (Pl. 64, figs. 8-10).

Dimensions.—Length of the apical spine 0.24, of the basal spines 0.16.

Habitat.—South Atlantic, Station 338, surface.

4. Plagoniscus nassellaris, n. sp.

Spines cylindrical, curved, irregularly branched. Apical spine half as long as, and less branched than the three basal spines, which are sigmoidal, nearly horizontally expanded in the proximal half, descending in the distal half.

Dimensions.—Length of the apical spine 0.1, of the three basal spines 0.18.

Habitat.—West Tropical Pacific, Station 224, surface.

Definition.— with four equal radial spines, arising in pairs from the two poles of a common central rod.

The genus Plagonidium, and the following Plagiocarpa possess four radial spines, like the two preceding genera. But whilst the four rods in these latter arise from a common centre, here they arise in two pairs from the two poles of a common middle rod; they have therefore exactly the same form which we find in the single spicula of some (e.g., Thalassoxanthium furcatum, Sphærozoum furcatum, &c.). Probably the middle rod is horizontal and serves as supporting base for the central capsule, whilst two opposite spines are directed upwards, two other downwards.

1. Plagonidium bigeminum, n. sp.

Spines straight, three-sided prismatic, four to six times as long as the common central rod, pinnate, with four to five pairs of opposite pinnulæ, the distal of which are simple, the proximal again branched.

Dimensions.—Length of the spines 0.16, of the middle rod 0.032.

Habitat.—Indian Ocean, Sunda Strait (Rabbe), surface.