All rings of the disk concentric, circular, of equal breadth. Pores regular, circular, everywhere of nearly equal size, three on the breadth of each ring, a little smaller in the equatorial girdle, which is about as broad as the radius of the disk. Twenty to twenty-four bristle-shaped radial spines, irregularly disposed, proceed with their free points over the margin.
Dimensions.—Diameter of the disk (with four rings) 0.1, with the girdle 0.3; breadth of each ring 0.011; pores 0.002.
Habitat.—North Pacific, Kamtschatka, Bailey.
4. Stylochlamydium æquale, Haeckel.
Perichlamydium æquale, Stöhr, 1880, Palæontogr., vol. xxvi. p. 109, pl. v. fig. 2.
All rings of the disk concentric, circular, with increasing breadth from the centre; the sixth ring twice as broad as the second. Pores regular, circular, everywhere of equal size; on the breadth of the inner rings one, of the outer two, of the girdle three pores. Girdle only one-fourth as broad as the radius of the disk. About twenty bristle-shaped radial spines, irregularly disposed, are connected by the girdle near to the points.
Dimensions.—Diameter of the disk (with six rings) 0.11, with the girdle 0.17; breadth of the second ring 0.006, of the sixth 0.013; pores 0.006.
Habitat.—Fossil in Tertiary rocks of Sicily, Grotte, Stöhr.
Subgenus 2. Stylochlamyum, Haeckel.
Definition.—Rings of the disk all (or in part) not concentric, spirally convoluted or irregular.