Page:Scientific results HMS Challenger vol 18 part 2.djvu/729

Rh as in the closely allied Aulosphærida (Pl. 111, fig. 3). The pseudopodia arising from the central capsule form a loose network in the calymma, and proceed over its surface as numerous delicate radial filaments, often supported by the radial spines.

Definition.— with a delicate spherical shell, the thin wall of which is composed of a simple lattice-plate, not spongy.

Definition..— with a delicate shell, the thin wall of which is composed of a simple smooth lattice-plate, without radial spines.

The genus Sagena is the simplest of the Sagosphærida and may be regarded as the common ancestral form of this family. The delicate wall of the simple spherical lattice-shell is composed of large, regular, or subregular, triangular meshes, the nodal points of which bear no radial spines. It agrees therefore perfectly with Aularia, and differs from this simplest form of Aulosphærida only in the structure of the skeleton, which is composed not of hollow articulated tubes, but of very thin solid threads. The skeleton may therefore also be confounded with Cenosphæra, but the central capsule of this latter is "peripylean," with numerous fine pores in the entire wall, whilst that of Sagena is "tripylean," having the proboscis of all.