former. Pores regular, circular, in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, on the margin prominent.
Dimensions.—Diameter of the disk (with six rings) 0.14; breadth of the inner rings 0.007, of the outer 0.013; pores 0.0017.
Habitat.—Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.
17. Porodiscus bispiralis, Haeckel.
All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the rings; the fourth ring twice as broad as the first. Pores regular, circular; in the inner rings one pore on the breadth, in the outer rings two to three pores. Radial beams piercing, numerous, prominent on the margin.
Dimensions.—Diameter of the disk (with four rings) 0.1; breadth of the inner rings 0.006, of the outer 0.012; pores 0.0015.
Habitat.—Fossil in the rocks of Barbados; living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.
18. Porodiscus duplex, Haeckel.
All rings of the disk spirally convoluted, in a perfect double spiral, with increasing breadth of the broad rings. Pores regular, circular; in the inner rings two to three, in the outer four to five on the breadth. Radial beams interrupted. Margin of the rings thorny.
Dimensions.—Diameter of the disk (with three rings) 0.15; breadth of the rings 0.02 to 0.04; pores 0.007.
Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.
19. Porodiscus semispiralis, n. sp. (Pl. 41, fig. 4).
All rings of the disk spirally convoluted, divided by four radial, perpendicularly crossed and zigzag shaped beams into four quadrants; the quarter rings of each quadrant halving the rings of each adjacent quarter. Half spiral line often irregular or partly interrupted. Breadth of all rings nearly equal. Pores irregular, roundish, two on the breadth of each ring. Margin of the disk dentated.
Dimensions.—Diameter of the disk (with nine rings) 0.22; breadth of each ring 0.012; pores 0.002 to 0.006.
Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.
Subgenus 5. Atactodiscus, Haeckel, 1881, Prodromus, p. 459.
Definition.—Rings of the disk more or less irregular, partly concentric, partly spirally convoluted, often interrupted.
