The Central Capsule of the Spongurida is either ellipsoidal or cylindrical. Only in Spongellipsis it lies freely in the internal cavity of the spongy shell. In all other genera it is perforated by a part of the skeleton; in the Spongodruppida it contains the simple or double medullary shell, and the radial beams which perforate its membrane and connect the latter with the external spongy cortical shell. In Spongurus and the allied genera (Spongocore, Spongoprunum) the whole central capsule is filled with a spongy framework which also envelops its surface.
Synopsis of the Genera of Spongurida.
| I. Subfamily Spongellipsida. (Ellipsoidal shell composed only of a spongy framework without a latticed medullary shell in the centre. |  | Spongy shell with internal cavity. |  | No polar spines, | 144. Spongellipsis. |
| Spongy shell solid, without internal cavity. |  | Without lattice mantle. No polar spines, | 145. Spongurus. | ||
| With lattice mantle. No polar spines, | 146. Spongocore. | ||||
| Without lattice mantle. Two opposite spines on the poles of the axis, | 147. Spongoprunum | ||||
| II. Subfamily Spongodruppida. (Ellipsoidal shell composed of an outer spongy cortical shell and an inner latticed medullary shell.) |  | Medullary shell simple. |  | No polar spines, | 148. Spongodruppa. |
| Two opposite spines on the poles of the axis, | 149. Spongatractus. | ||||
| Medullary shell double. | | No polar spines, | 150. Spongoliva. | ||
| Two opposite spines on the poles of the axis, | 151. Spongoxiphus. |
| I. Subfamily Spongellipsida. (Ellipsoidal shell composed only of a spongy framework without a latticed medullary shell in the centre. | ||||||
| Spongy shell with internal cavity. | ||||||
| No polar spines, | ||||||
| 144. Spongellipsis. | ||||||
| Spongy shell solid, without internal cavity. | ||||||
| Without lattice mantle. No polar spines, | ||||||
| 145. Spongurus. | ||||||
| With lattice mantle. No polar spines, | ||||||
| 146. Spongocore. | ||||||
| Without lattice mantle. Two opposite spines on the poles of the axis, | ||||||
| 147. Spongoprunum | ||||||
| II. Subfamily Spongodruppida. (Ellipsoidal shell composed of an outer spongy cortical shell and an inner latticed medullary shell.) | ||||||
| Medullary shell simple. | ||||||
| No polar spines, | ||||||
| 148. Spongodruppa. | ||||||
| Two opposite spine on the poles of the axis, | ||||||
| 149. Spongatractus. | ||||||
| Medullary shell double. | ||||||
| No polar spines, | ||||||
| 150. Spongoliva. | ||||||
| Two opposite spine on the poles of the axis, | ||||||
| 151. Spongoxiphus. | ||||||
Subfamily 1. Spongellipsida, Haeckel.
Definition.—Spongurida with a spongy ellipsoidal or cylindrical shell, without an internal latticed medullary shell.
Genus 144. Spongellipsis,[[183]] n. gen.
Definition.—Spongurida with an ellipsoidal or cylindrical spongy shell, containing an internal cavity, without a latticed medullary shell. Polar spines absent.
The genus Spongellipsis embraces those very simple Spongurida in which the ellipsoidal central capsule is enclosed in a spongy cortical shell of the same form. It corresponds, therefore, to Plegmosphæra among the Sphæroidea, to Plegmodiscus among the Discoidea, and to Spongolarcus among the Larcoidea. In some species the ellipsoidal form is prolonged and passes into a cylindrical one.