Page:Scientific results HMS Challenger vol 18 part 1.djvu/787

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Definition.— with a simple circular disk, without radial appendages, on the margin surrounded by a thin porous or solid equatorial girdle.

The genus Spongophacus, represented hitherto only by a single but interesting species, differs from Spongodiscus by the peculiar girdle which surrounds the margin of the disk in the equatorial plane. It simulates the same formation as Perichlamydium in the Porodiscida, and resembles also Periphæna, &c., in the Phacodiscida.

1. Spongophacus periphæna, n. sp.

Spongy disk lenticular, with an irregular, dense framework, in the centre darker than in the peripheral part. Margin of the disk very thin, surrounded by a broad, circular girdle, lying in the equatorial plane, about as broad as the half radius of the spongy disk. The inner part of the girdle is perforated by numerous irregular, small pores, which pass over gradually into the spongy meshes; the outer part is quite homogeneous, solid, transparent, with an extremely thin margin.

Dimensions.—Diameter of the disk 0.2; breadth of the girdle 0.05.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Definition.— with a circular disk, the margin of which is armed with solid radial spines, situated in the equatorial plane (rarely also on both sides of the disk with radial spines).

Definition.— with two solid marginal spines, opposite in one equatorial diameter of the disk.

The genus Spongolonche opens the series of the Spongotrochida, or of those Spongodiscida in which the margin of the disk is armed with solid radial spines, situated in the equatorial plane. Spongolonche possesses only two such spines, opposite in one equatorial diameter of the disk; it corresponds therefore to Stylocyclia among the Coccodiscida, to Xiphodictya among the Porodiscida.