Subfamily Hexalonchida,[[104]] Haeckel, 1881, Prodromus, pp. 449, 451.
Definition.—Cubosphærida with two concentric spherical lattice-shells.
Genus 75. Hexalonche,[[105]] Haeckel, 1881, Prodromus, p. 451.
Definition.—Cubosphærida with two concentric lattice-spheres and six simple spines of equal size.
The genus Hexalonche is the most simple form, and probably the common ancestral form, of all Hexalonchida, or those Cubosphærida which possess two concentric latticed spheres, connected by six radial beams. Commonly one shell is intracapsular (medullary shell) and the other extracapsular (cortical shell); but sometimes also both shells are extracapsular, and these forms may perhaps be better separated as a peculiar genus Hexadilemma. In Hexalonche all six simple spines are of equal size, and opposite by pairs in three equal dimensive axes, corresponding to the three equal axes of a tesseral crystal. It can be derived from Hexastylus by duplication of the lattice-shell.
Subgenus 1. Hexalonchara, Haeckel.
Definition.—Pores of the cortical shell regular or subregular, of nearly equal size and similar form; surface smooth, without radial by-spines (other than the six main spines).
1. Hexalonche phænaxonia, n. sp.
Cortical shell thin walled, smooth; its pores regular, hexagonal, six to eight times as broad as the bars; eight to ten to twelve on the radius. Medullary shell one-third as broad, with regular, hexagonal pores of half size. Six spines triangular pyramidal, as long as the radius of the shell, at the base as broad as one pore. (Differs from Hexastylus phænaxonius, Pl. [21], fig. 3, only in the medullary shell and the six inner radial beams, connecting it with the cortical shell.)
Dimensions.—Diameter of the outer shell 0.15, pores 0.01 to 0.015, bars 0.015 to 0.02; inner shell 0.05; length of the spines 0.08, basal breadth 0.01.