Page:Scientific results HMS Challenger vol 18 part 1.djvu/754

546 Dimensions.—Radius of each arm 0.12, basal breadth 0.013, distal breadth 0.04.

Habitat.—Fossil in the rocks of Barbados; and living in the depth of the Central Pacific, Station 268, depth 2900 fathoms.

6. Histiastrum boseanum, n. sp. (Pl. 46, fig. 1).

Arms linear, twelve times as long as broad at their base (at their distal end twice as broad as at their base), with rectilinear, parallel edges. The club-shaped end thickened, dentate, with two lateral rows of strong teeth in the equatorial plane, and with one very stout, angular, terminal spine. Central disk with two to three rings, broader than the arms. Patagium incomplete, with four to five concave chamber-rows, enveloping only the basal half of the arms. I call this splendid species in honour of Dr. Graf Bose, the great friend of nature and patron of the University of Jena.

Dimensions.—Radius of each arm 0.25, basal breadth 0.02, distal breadth 0.05.

Habitat.—Indian Ocean, Madagascar, Rabbe.

7. Histiastrum coronatum, n. sp.

Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. iv. fig. 1.

Arms linear, eight times as long as broad, with rectilinear parallel edges; the thickened, nearly spherical, distal end three times as broad, with five strong conical spines, one middle (perradial) larger and two smaller on each side of it. Central disk with two to three rings, of the same breadth as the terminal knot of the arms. Patagium incomplete, square, enveloping the arms, with the exception of the knot.

Dimensions.—Radius of each arm 0.16, basal breadth 0.02, terminal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados.

8. Histiastrum circulare, n. sp.

Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. xxiii. fig. 1.

Arms linear in their inner half, egg-shaped and three times as broad in their outer half, with ten to twelve strong terminal spines, the middle (perradial) larger, in all three times as long as broad. Central disk with three to four rings, broader than their distal knobs. Patagium nearly complete, circular, enveloping the whole arms, with exception of the outermost end.

Dimensions.—Radius of each arm 0.22, basal breadth 0.02, terminal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados; and living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.

9. Histiastrum pentadiscus, n. sp. (Pl. 46, fig. 2).

Arms in their inner half linear, twice as long as broad, in their outer half circular, three times as broad, with the same structure as the central disk, exhibiting three concentric rings around one