8. Porodiscus heterocyclus, Haeckel.
Trematodiscus heterocyclus, Haeckel, 1862, Monogr. d. Radiol., p. 493, Taf. xxix. fig. 3.
? Flustrella cyclia, Harting, 1863, Fauna Banda-Zee, p. 11, pl. i. fig. 19.
Trematodiscus heterocyclus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108.
All rings of the disk concentric, circular, connected by numerous radial beams, which are partly piercing, partly alternating. The breadth of the rings increases gradually from the centre towards the periphery, corresponding also to the size of the pores; two to three circular pores on the breadth of each ring.
Dimensions.—Diameter of the disk (with six rings) 0.17; breadth of the second ring 0.007, of the sixth 0.02; pores 0.002 to 0.006.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in Tertiary rocks of Barbados and the Mediterranean.
9. Porodiscus quadrigatus, n. sp. (Pl. [41], fig. 3).
All rings of the disk concentric, of nearly equal breadth, connected by four interradial beams, perpendicular one to another. The first ring (surrounding the central chamber) with eight chambers, the second only with four (alternating with the four radial beams). Size of the four chambers of each ring increases much towards the periphery. Pores regular, circular, about two on the breadth of each ring.
Dimensions.—Diameter of the disk (with six rings) 0.18; breadth of each ring 0.05; pores 0.004.