Page:Scientific results HMS Challenger vol 18 part 1.djvu/498

290 The central capsule of the Ellipsida is in all cases ellipsoidal, and occupies the largest part of the shell, being separated from its inner surface by a thinner or thicker jelly-mantle.

Definition.— with simple ellipsoidal shell, without radial spines and without polar tubes.

The genus Cenellipsis is the simplest and most primitive form, not only among the Ellipsida, but also among the, and it may therefore be regarded as the common ancestral form of the whole family. It corresponds to Cenosphæra among the, to Cenodiscus among the , to Cenolarcus among the. Probably it is derived from Cenosphæra by prolongation of one axis.

Definition.—Network of the shell regular, with meshes of equal size and similar form.