Disk with radiated surface, four times as broad as the medullary shell. Pores regularly circular; nine to ten on the radius of the disk, arranged in radial series (about forty), which are separated by smooth crests, not prominent on the smooth margin.
Dimensions.—Diameter of the disk 0.12, of the medullary shell 0.03, of the pores 0.003.
Habitat.—Fossil in Tertiary deposits of the Mediterranean, Greece, Sicily, Oran, &c.
8. Sethodiscus echinatus, Haeckel.
Haliomma echinatum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. fig. 2.
Disk with radiated thorny surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius of the disk, arranged in radial series (about sixty), which are separated by thorny crests, prominent a little on the dentated margin.
Dimensions.—Diameter of the disk 0.18, of the medullary shell 0.06, of the pores 0.01.
Habitat.—Fossil in the rocks of Barbados.
9. Sethodiscus cristatus, n. sp.
Disk with radiated surface, four times as broad as the medullary shell. Pores regularly circular; sixteen to seventeen on the radius of the disk, arranged in radial series (about eighty), which are separated in the distal half by smooth elevated crests, strongly prominent on the dentated margin. (Very similar to Phacodiscus cristatus, Pl. [35], fig. 6, but with simple medullary shell.)