Page:Scientific results HMS Challenger vol 18 part 1.djvu/753

Rh somewhat broader than their distal end. Patagium incomplete, connecting only the basal half of the arms, with three to four concave chamber-rows, on the margin concave. (May be regarded as Euchitonia mülleri, with four arms.)

Dimensions.—Radius of each arm 0.2, basal breadth 0.05, distal breadth 0.1.

Habitat.—Atlantic, surface, Canary Islands.

3. Histiastrum velatum, n. sp. (Pl. 46, fig. 4).

Dictyastrum velatum, Haeckel, 1879, Atlas (pl. xlvi. fig. 4).

Arms pear-shaped, rapidly increasing from their narrow base, nearly circular, little longer than broad; each with eight to nine transverse chamber-rows; their lateral edges at their base concave, at their end circular. Central disk with three to four rings, somewhat smaller than one arm. Patagium complete, with six to seven radial beams, filling out perfectly the intervals between the arms. A peculiar girdle of finer network and equal breadth surrounds the whole equatorial periphery of the disk, and gives it the appearance of a square with rounded corners.

Dimensions.—Radius of each arm 0.2, basal breadth 0.03, distal breadth 0.12.

Habitat.—South Atlantic, Station 330, surface.

Definition.—Distal ends of the arms spiny, furnished with one or more terminal spines.

4. Histiastrum quaternarium, Ehrenberg.

Histiastrum quaternarium, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxiv. figs. 3, 4.

Arms six times as long as broad at their base, with rectilinear, little divergent edges; at their truncated distal end a little broader, with one single, very strong, conical, terminal spine. Central disk with four to five rings, somewhat broader than the arm. Patagium incomplete, enveloping only the basal half of the arms.

Dimensions.—Radius of each arm 0.18, basal breadth 0.03, distal breadth 0.05.

Habitat.—Fossil in the rocks of Barbados.

5. Histiastrum gladiatum, n. sp.

Astromma sp., Bury, 1862, Polycystins of Barbados, pl. v. fig. 1.

Arms triangular, eight times as long as broad at their base; at their distal end three times as broad as at their base, with rectilinear, divergent edges; their truncated end with a large conical, terminal spine. Central disk with four to five rings, broader than the arms. Patagium incomplete, enveloping only the basal half of the arms.