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.
2. Plagonidium quadrigeminum, n. sp.
Spines cylindrical, curved, eight to ten times as long as the common central rod, in the distal half forked; the fork-branches curved, somewhat longer than the basal part.
Dimensions.—Length of the spines 0.18, of the middle rod 0.02.
Habitat.—Antarctic Ocean, Kerguelen Island, Station 159, surface.
Genus 389. Plagiocarpa,[[8]] Haeckel, 1881, Prodromus, p. 424.
Definition.—Plagonida with four unequal radial spines, arising in pairs from the two poles of a common central rod; one ascending apical spine opposed to three descending basal spines.
The genus Plagiocarpa agrees with the preceding Plagonidium in the possession of a common horizontal middle rod, the two poles of which bear two pairs of divergent spines; but whilst in the preceding all four spines are equal, here they are differentiated in the same manner as in Plagoniscus, which differs only in the absence of the middle rod. The two observed and closely allied species of this genus are of peculiar interest, since they belong possibly to the common ancestral forms of the Nassellaria; the basal middle rod corresponds perhaps to the basal part of a sagittal ring, the apical spine to its dorsal part, the three other spines to the basal feet (compare above, p. [902]).