6. Porodiscus microporus, Haeckel.
Trematodiscus microporus, Stöhr, 1880, Palæontogr., vol xxvi. p. 108, Taf. iv. fig. 17.
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.
7. Porodiscus ellipticus, Haeckel.
Trematodiscus ellipticus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 108, Taf. iv. fig. 16.
All rings of the disk concentric, either circular or a little elliptical, connected by eight piercing radial beams; central chamber elliptical, of the same breadth as the first ring, broader than the following rings, the breadth of which decreases towards the periphery. Pores irregular, in the inner rings twice as broad as in the outer (third) ring, four to five on the breadth of each ring.
Dimensions.—Diameter of the disk (with three rings) 0.18; breadth of the inner rings 0.03, of the outer 0.02; pores 0.003 to 0.006.
Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.