Definition.—Stylosphærida with four concentric lattice-spheres and two free spines of different size or form.
The genus Cromyostylus differs from its ancestral form, Stylocromyum, in the differentiation of the two unequal polar spines.
1. Cromyostylus gladius, n. sp.
Surface of the shell smooth. Radial proportion of the four spheres = 1 : 3 : 10 : 12. Both medullary shells with regular, circular, simple pores. Inner cortical shell with regular, circular, hexagonally framed pores, twice as broad as the bars. From each hexagon-corner arises a bristle-shaped radial spine, which at the distal end gives off three thread-like branches; by communication of these threads (at equal distances from the centre) the delicate outer medullary shell is formed. The polar spines very different; major spine six-sided pyramidal, longer than the diameter of the shell; minor pommel-shaped, shorter than the radius (similar to Xiphatractus glyptodon, Pl. [17], figs. 9, 10, but different in the double spherical cortical shell).
Dimensions.—Diameter of the four spheres—(A) 0.02, (B) 0.06, (C) 0.2, (D) 0.24; length of the major spine 0.3, of the minor 0.1.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
Subfamily Caryostylida, Haeckel, 1881, Prodromus, pp. 449, 454.
Definition.—Stylosphærida with five or more concentric, spherical lattice-shells.
Genus 56. Caryostylus, Haeckel, 1881, Prodromus, p. 454.
Definition.—Stylosphærida with five to six or more concentric lattice-shells and two free opposite spines of equal size and similar form.