Page:Scientific results HMS Challenger vol 18 part 1.djvu/735

Rh the roundish central disk, whilst their length reaches only one-fourth of it. End of the arms convex rounded, without spines.

Dimensions.—Radius of each arm 0.1, breadth 0.15.

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

2. Rhopalastrum pistillum, Stöhr.

Rhopalastrum pistillum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 110, Taf. v. fig. 4.

Distance between the paired arms about two-thirds as large as their distance from the odd arm. All three arms nearly of the same form and size, about three times as long as the diameter of the central disk, at the base one-third as broad as at the convex rounded end, without spines. Stöhr has only observed a fragment with one arm; some perfect specimens, which I found in the Caltanisetta-rock, exhibited nearly the same form as Rhopalastrum malleus (Pl. 43, fig. 1), but differ from this by the smaller disk, the broader arms, and the smaller angle between the paired arms.

Dimensions.—Radius of all three arms 0.2; basal breadth of each arm 0.045, terminal breadth 0.13.

Habitat.—Fossil in Tertiary rocks of Sicily, Grotte (Stöhr), Caltanisetta (Haeckel).

3. Rhopalastrum malleus, n. sp. (Pl. 43, fig. 1).

Distance between the paired arms one and a third times as large as their distance from the odd arm. All three arms nearly of the same form and size, hammer-shaped, three times as broad at the truncated distal end as at the base. Central disk broader than the arms.

Dimensions.—Radius of each arm 0.25, basal breadth 0.05, distal breadth 0.15.

Habitat.—South Atlantic, Station 325, surface.

4. Rhopalastrum lagenosum, Ehrenberg.

Rhopalastrum lagenosum, Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 43; Mikrogeol., 1854, Taf. xxii. fig. 22.

Rhopalastrum lagenosum, Haeckel, 1862, Monogr. d. Radiol., p. 501.

Flustrella bilobata, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 81.

Haliomma lagena, Ehrenberg, 1840, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 200.

Distance between the paired arms one and a half times as great as their distance from the odd arm. All three arms nearly of the same form and size, about one and a half times as long as the diameter of the central disk, at the base half as broad as at the convex rounded end, without spines. Ehrenberg has only observed a fragment with two paired arms; some perfect specimens with three arms, observed by me, differed from the nearly allied Rhopalastrum pistillum (from the same locality) by the larger disk, the broader arms, and the larger unpaired angle.

Dimensions.—Radius of all three arms 0.2, basal breadth 0.05, terminal breadth 0.09.

Habitat.—Fossil in Tertiary rocks of Sicily, Caltanisetta.