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 #Beloidea# (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. {914}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). 1. _Plagiocarpa procortina_, n. sp. (Pl. 91, fig. 5). Spines cylindrical, curved, thorny, three to four times as long as the common middle rod. Apical spine and the meeting caudal spine (or the posterior basal spine) somewhat longer and with more numerous thorns than the two paired pectoral (or anterior) spines. From the common base of the latter arises an anterior prolongation of the horizontal middle rod, which in the sagittal plane is curved upwards and corresponds to the sternal foot of many #Cyrtellaria#. An ascending branch of this spine is opposed to a descending branch of the apical spine, both together forming an incomplete sagittal ring.