The central capsule is lentelliptical, encloses the medullary shell, and is enveloped by the cortical shell, as in the nearly allied Pylonida and Larnacida, of which the Phorticida may be regarded as irregular aberrant forms.
Synopsis of the Genera of Phorticida.
| Cortical shell simply latticed, | 313. Phorticium. |
| Cortical shell spongy, | 314. Spongophortis. |
Genus 313. Phorticium,[[353]] Haeckel, 1881, Prodromus, p. 464.
Definition.—Phorticida with irregular cortical shell of simple lattice-work, enclosing a lentelliptical Larnacilla-shaped medullary shell.
The genus Phorticium comprises all Phorticida in which the irregular cortical shell is formed by simple lattice-work, not by spongy framework. We can divide this genus into two subgenera: in Phortopyle (as in the Pylonida) the lattice-work of the cortical shell exhibits large openings or gates; in Phortolarcus these gates are perfectly closed by network; the former may be regarded as abnormal or irregular Pylonida, the latter as modifications of Larnacida.
Subgenus 1. Phortopyle, Haeckel.
Definition.—Lattice-work of the irregular cortical shell incomplete, with large openings or gates.
1. Phorticium pylonium, n. sp. (Pl. [49], fig. 10).
Cortical shell irregular, roundish, about three times as large as the enclosed lentelliptical, regular, Larnacilla-shell, connected with it by some radial beams and irregularly latticed girdles; between these remain four to eight large open gates of irregular roundish form and size; and these gates are the same as in Tetrapyle and Octopyle. This very variable species may be regarded as a monstrosity of those genera of Pylonida; it is very common, but all individuals are more or less unequal; some specimens approach to some common species of Tetrapyle. The surface of the shell is more or less spiny.