Page:Scientific results HMS Challenger vol 18 part 1.djvu/804

596 6. Spongasteriscus quadricornis, Haeckel.

Spongasteriscus quadricornis, Haeckel, 1862, Monogr. d. Radiol., p. 474, Taf. xxviii. figs. 8-10.

Spongodiscus quadricornis, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; their form equilateral triangular; their length smaller than the radius of the large circular central disk, which exhibits in the interior eight to sixteen concentric rings.

Dimensions.—Radius of the arms 0.2, of the central disk 0.13; basal breadth of the arms 0.08.

Habitat.—Mediterranean (Messina), Haeckel, surface.

7. Spongasteriscus tetraceros, Haeckel.

Spongasteriscus tetraceros, Haeckel, 1862, Monogr. d. Radiol., p. 475.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; their form isosceles triangular; their length larger than the radius of the large elliptical central disk, which exhibits in the interior six to twelve concentric rings.

Dimensions.—Radius of the arms 0.16, of the central disk 0.1; basal breadth of the arms 0.06.

Habitat.—Mediterranean (Messina), North Atlantic (Canary Islands), surface.

8. Spongasteriscus myelastrum, n. sp.

Arms at different distances, forming a bilateral or irregular cross, grouped in two opposite pairs; the arms of one pair broader and shorter than the arms of the other pair. Each arm in its basal half simple, in the distal half forked; ends of the fork branches blunt. In the central disk no concentric rings. (Similar to Myelastrum octocorne, Pl. 47, fig. 12, but quite spongy.)

Dimensions.—Radius of the arms 0.2, basal breadth 0.05, distal breadth 0.02.

Habitat.—North Pacific, Station 236, surface.

Definition.— with four spongy arms on the margin of the circular or quadrangular disk, connected by a spongy patagium of different texture.

The genus Spongaster differs from the foregoing Spongasteriscus in the patagium connecting the spongy arms, and bears therefore to it the same relation as, in the Porodiscida, Histiastrum does to Stauralastrum, or, in the Coccodiscida, Stauractura does to Astractura. The typical specimen, figured by Ehrenberg (Spongaster tetras), exhibits a regular, square disk, as also some other species. In a certain number of other species (formerly united by me with Spongocyclia) the quadrangular disk is bilateral.