Spines straight and stout, three-sided prismatic, about four times as long as the common middle rod, gradually thinned towards the distal end; in the basal half with two to three verticils of forked branches, which are dichotomously ramified, and by their united threads form a loose ovate framework. _Dimensions._--Length of the spines 0.17, of the middle rod 0.04. _Habitat._--North Pacific, Station 236, surface. 3. _Plectanium sphærozoum_, n. sp. Spines straight, cylindrical, ten to twelve times as long as the common middle rod, with six to eight verticils of thorny branches, tapering towards the distal end; the branches of the verticils are simple in the distal half, again ramified in the basal half, and here connected together by irregularly branched threads forming a loose framework. (Resembles one spiculum of _Sphærozoum verticillatum_, Pl. 4, fig. 7, but is more richly branched, with united ramules.) _Dimensions._--Length of the spines 0.2, of the middle rod 0.01. _Habitat._--Central Pacific, Station 266, surface. {929}Subfamily 4. POLYPLECTIDA, Haeckel, 1881, Prodromus, p. 424. _Definition._--#Plectanida# with numerous (seven to nine or more) radial spines. Genus 400. _Polyplecta_,[19] Haeckel. _Definition._--#Plectanida# with numerous (seven to nine or more) radial spines, arising from a common centre and lying in different planes. The genus _Polyplecta_ comprises provisionally all Plectanida possessing seven or more radial spines, united in the centre of the framework. It may be derived from _Polyplagia_ by meeting and concrescence of the free branches. But as in the latter genus, here also the few observed species are very different, perhaps of different origin, and may be afterwards better separated as representatives of diverse genera. 1. _Polyplecta heptacantha_, n. sp. (Pl. 91, fig. 12). _Heptaplegma heptacantha_, Haeckel, 1882, MS. Seven unequal spines divergent from one common central point, slender, slightly curved, three-sided prismatic. Four spines are much larger, twice to three times as long and as thick as the three smaller spines. One of the four larger spines is directed upwards (as "apical horn"), whilst the three others diverge downwards (as "basal feet"). Each of the four larger spines bears five to seven equidistant verticils of three divergent branches, the proximal of which are branched, the distal simple. The three smaller spines lie nearly horizontally, midway between the odd apical spine and the three basal spines, and in the same meridian planes with them; each bears one verticil of three divergent branches. All the branches are united by arachnoidal threads, composing a loose wickerwork with irregular, generally quadrangular meshes. _Dimensions._--Length of the four larger spines 0.27 to 0.33, of the four smaller 0.1 to 0.14. _Habitat._--Central Pacific, Station 271, surface. 2. _Polyplecta enneacantha_, n. sp. _Enneaplegma enneacantha_, Haeckel, 1881, Prodromus, p. 425.