Page:Scientific results HMS Challenger vol 18 part 1.djvu/360

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Definition.— with one single spherical lattice-shell.

Definition.— with a single lattice-sphere and four crossed equal spines.

The genus Staurosphæra may be regarded as the common ancestral form of this subfamily, since it represents their most simple and primitive form. From the surface of the simple lattice-sphere, enclosing the central capsule, arise four equal, simple, radial spines, opposite in pairs in two diameters, perpendicular one to another. Staurosphæra may be derived phylogenetically either from Cenosphæra by production of the four spines, or from Hexastylus by reduction of two opposite spines.