4. Stylotrochus rhabdostylus, Haeckel.
Spongosphæra rhabdostyla, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 256, Taf. xxvi. figs. 1, 2.
Spongy framework of the whole disk irregular. Four very large marginal primary spines crossed in two equatorial diameters, perpendicular one to another, and between them numerous (twelve to twenty or more) smaller secondary spines. The latter arise from the margin, whilst the former pierce the disk and are nearly united in its centre. All the spines are cylindrical, the smaller as broad as one mesh, the larger three to six times as broad.
Dimensions.—Diameter of the disk 0.2; length of the four main spines 0.15 to 0.3, breadth 0.01 to 0.02; length of the accessory spines 0.05 to 0.1, breadth 0.005.
Habitat.—Fossil in the rocks of Barbados.
5. Stylotrochus heteracanthus, Haeckel.
Spongotrochus heteracanthus, Haeckel, 1862, Monogr. d. Radiol., p. 464.
Spongy framework of the whole disk irregular. Ten very long needle-shaped marginal spines (symmetrically distributed), and between them numerous very fine, shorter, accessory, bristle-shaped spines.
Dimensions.—Diameter of the disk 0.16; length of the main spines 0.16, basal breadth 0.002; length of the secondary spines 0.03.
Habitat.—Mediterranean (Messina), surface.