Page:Scientific results HMS Challenger vol 18 part 1.djvu/750

542 8. Stauralastrum staurolonche, n. sp.

Arms four times as long as broad at their base, gradually increasing towards their truncated end, which is one and a half times as broad as their base; their distal breadth equals the radius of the central disk, which exhibits four to five rings. At the end of each arm is a very strong conical terminal spine. (Resembles Histiastrum quaternarium, Abhandl. k. Akad. Wiss. Berlin, 1875, Taf. xxiv. fig. 3, but has no patagium.) Edges of the arms rectilinear, divergent.

Dimensions.—Radius of each arm 0.25, basal breadth 0.045, distal breadth 0.07.

Habitat.—Fossil in the Barbados rocks; and living in the depth of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

9. Stauralastrum horridum, n. sp.

Arms three times as long as broad at their base, gradually increasing towards their rounded end, which is twice as broad as their base, their distal breadth equals the diameter of the central disk, which exhibits four to five rings. Surface thorny, at the distal end of each arm is a group of twenty to twenty-five smaller and five to six larger, straight, conical spines. Edges of the arms rectilinear, divergent.

Dimensions.—Radius of each arm 0.15, basal breadth 0.05, distal breadth 0.1.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

Definition.— with four simple, undivided, chambered arms, without a patagium; quadrangular shell bilateral, two opposite arms of the main axis (or principal arms) different from the two others (or lateral arms).

The genus Hagiastrum, as here defined, was formerly united by me with the foregoing Stauralastrum, but differs from it by the bilateral or symmetrical form. Whilst in the latter all four arms and the four angles between them are equal, they are here differentiated into pairs.

Definition.—Both longitudinal arms of equal size and form.

1. Hagiastrum buddhae, n. sp. (Pl. 45, fig. 5).

Cross rectangular. Both longitudinal arms of equal size, twice as long as the transverse arms; all arms smooth, club-shaped, twice as broad at their globose distal part as at their base, each with three large conical terminal spines.