Haliomma triactis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 236, Taf. xxviii. fig, 4.
Disk with thorny surface and spiny margin, three times as broad as the medullary shell. Pores regular, circular; eight to nine on the radius of the disk. Three radial spines of different size and at unequal distances, one odd spine as long as the radius, both paired spines as long as the diameter of the disk; the odd angle between the latter is smaller. Spines pyramidal, with broad edges.
Dimensions.—Diameter of the disk 0.16, of the medullary shell 0.05, pores 0.008.
Habitat.—Fossil in the rocks of Barbados.
Genus 188. Sethostaurus,[[227]] Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with simple medullary shell and with four radial spines on the margin of the disk, crossed in the equatorial plane.
The genus Sethostaurus exhibits four marginal spines, which form commonly a more or less regular cross in the equatorial plane. Sometimes the size and disposition of the four spines become more or less different, and also the angles between them vary; the regular rectangular cross passes over into a bilateral or irregular form. The medullary shell is simple. The same cross-form of the disk is seen in Staurocyclia among the Coccodiscida, and in Staurodictya among the Porodiscida.
Subgenus 1. Sethostaurium, Haeckel.
Definition.—Margin of the disk without a solid equatorial girdle or a corona of spines.
1. Sethostaurus orthostaurus, n. sp. (Pl. [31], figs. 1, 2).