3. Porodiscus flustrella, n. sp. (Pl. 41, fig. 1).
All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers different in size, increasing from the centre towards the periphery. Pores very irregular, polygonal, or roundish, one to three on the breadth of each ring.
Dimensions.—Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.002 to 0.006.
Habitat.—Cosmopolitan; Atlantic, Pacific, &c., many Stations, surface.
4. Porodiscus sorites, Haeckel.
All rings of the disk circular, concentric, of equal breadth, connected by numerous alternating radial beams. Chambers different in size, increasing from the centre. Pores regular, circular, one to one and a half on the breadth of each ring.
Dimensions.—Diameter of the disk (with six rings) 0.12; breadth of each ring 0.01; pores 0.006.
Habitat.—Mediterranean (Messina), surface.
5. Porodiscus macroporus, Haeckel.
All rings of the disk circular, concentric, of equal breadth, connected by numerous piercing radial beams. Chambers of different breadth, increasing from the centre. Pores regular, very large, nearly square, one single pore on the breadth of each ring.
Dimensions.—Diameter of the disk (with five rings) 0.11; breadth of each ring 0.01; pores 0.005.
Habitat.—Fossil in the Tertiary rocks of Barbados.
6. Porodiscus microporus, Haeckel.
All rings of the disk concentric, either circular or a little elliptical; the innermost rings of the same breadth as the central chamber, the third ring much broader. Radial beams between them alternating; chambers of different size. Pores very small, subregular, everywhere of the same size, four to five pores on the breadth of each ring.
Dimensions.—Diameter of the disk (with three rings) 0.15; breadth of the inner rings 0.02, of the outer 0.03; pores 0.0016.
Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.
