| I. Subfamily Oronida. Surface of the shell without pyramidal or tent-shaped elevations. | ||||
| Surface smooth, without radial spines, | ||||
| 671. Orona. | ||||
| Surface studded with simple or branched radial spines, | ||||
| 672. Orosphæra. | ||||
| II. Subfamily Oroscenida. Surface of the shell with numerous pyramidal or tent-shaped elevations. | ||||
| Pyramids of the surface free, without spongy envelope, | ||||
| 673. Oroscena. | ||||
| Pyramids of the surface connected by a spongy envelope or an external lattice-shell, | ||||
| 674. Oroplegma. | ||||
Genus 671. Orona,[[289]] n. gen.
Definition.—Orosphærida with a simple spherical or slightly ellipsoidal shell, without pyramidal elevations and radial spines.
The genus Orona is the simplest of the Orosphærida, and probably the common ancestral form of this family. The lattice-shell is a simple fenestrated sphere, sometimes slightly ellipsoidal, with prolonged main axis, and bears on its surface neither tent-shaped elevations nor radial spines. It may be confounded with some big forms of Cenosphæra; it differs, however, in the possession of hollow central canals in the thick bars of the very coarse lattice-plate.
1. Orona maxima, n. sp. (Pl. [107], fig. 5).
Shell spherical, with very irregular polygonal meshes. Bars of the loose network smooth or slightly spinulate, very thick, with a pinnulate axial canal.
Dimensions.—Diameter of the sphere 5.0 to 5.5, of the meshes 0.2 to 0.4, of the bars 0.01.
Habitat.—Central Pacific, Station 265, depth 2900.
2. Orona robusta, n. sp.
Shell spherical, with irregular quadrangular meshes (intermingled with single triangular, pentagonal, and hexagonal meshes). Bars of the coarse network very thick, spinulate.