The genus _Toxarium_ differs from its ancestral form _Acrocubus_ in the development of two pairs of peculiar bows, placed in the lateral or frontal plane; the upper pair projects above the mitral gates, and may be called the "galear bows," the lower pair projects below the basal gates of the cubical shell, and may be called the "thoracal bows." Both pairs are produced originally by the development of two forked vertical spines, arising in the frontal plane on both poles of the principal axis from the sagittal ring (compare _Protympanium amphipodium_, Pl. 93, fig. 14). The apical fork-branches become connected with the lateral corners of the mitral gates, the basal branches with those of the basal gates. By development of lattice-work between the bows and the rings some #Spyroidea# (_Amphispyris_, &c.) may have arisen. The important genus _Toxarium_ may be divided into three subgenera. In _Toxellium_ all the bows are simple, in _Toxonium_, all are forked; in _Toxidium_, the galear bows are simple, the thoracal bows forked. Subgenus 1. _Toxellium_, Haeckel. _Definition._--Galear and thoracal bows simple. 1. _Toxarium circospyris_, n. sp. (Pl. 88, fig. 1). Galear and thoracal bows simple, of about the same size as the frontal bows between them; all bows armed with scattered simple conical spines. Sagittal constriction deep, half as long as the whole shell. Lateral outlines of the shell nearly parallel. _Dimensions._--Length of the shell 0.16, breadth 0.13. _Habitat._--Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms. {996}2. _Toxarium subcirculare_, n. sp. Galear and thoracal bows simple, armed with scattered simple spines of about equal size, smaller than the smooth frontal bows between them. Sagittal constriction very flat. Therefore the frontal perimeter of the shell is nearly circular. _Dimensions._--Length of the shell 0.15, breadth 0.14. _Habitat._--North Atlantic (Antilles), Weber, surface. 3. _Toxarium thorax_, n. sp. (Pl. 93, fig. 18). Galear bows simple, smaller than the frontal bows, and these again smaller than the simple thoracal bows; therefore the shell increases in breadth towards the base, and resembles the skeleton of the thorax of one of the higher vertebrates (the bow-pairs corresponding to rib-pairs, the ventral part of the sagittal ring to the sternum, the dorsal part to the vertebral column). Sagittal constriction very deep. All bows are armed with scattered, irregularly branched spines. _Dimensions._--Length of the shell 0.17, breadth 0.2. _Habitat._--Central Pacific, Station 265, depth 2900 fathoms. 4. _Toxarium constrictum_, n. sp. Galear and thoracal bows simple, of nearly equal size, larger than the frontal bows between them. Therefore the shell is constricted in the equatorial plane. Sagittal constriction also deep. All bows armed with scattered, irregularly branched spines. _Dimensions._--Length of the shell 0.14, breadth 0.12. _Habitat._--North Pacific, Station 236, surface.