Page:Scientific results HMS Challenger vol 18 part 1.djvu/651

Rh regularly disposed, of variable size, the longest as long as the radius, pyramidal, not broader at the base than one pore, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.12, of the outer medullary shell 0.06, inner 0.02; length of the marginal spines 0.03 to 0.06, basal breadth 0.01.

Habitat.—Western Pacific, Philippine Sea, 3300 fathoms, Ehrenberg; Station 225, depth 4475 fathoms.

4. Astrosestrum acraspedum, n. sp.

Disk with smooth surface, three times as broad as the outer and six times as broad as the inner medullary shell. Pores regular, circular; nine to ten on the radius of the disk. Eight marginal spines regularly disposed, of alternating size; four major (perradial) spines as long as the diameter of the disk, four minor (interradial) half as long; spines cylindrical, not broader at the base than one pore, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.2, of the outer medullary shell 0.07, of the inner 0.035; length of the larger spines 0.2, of the smaller 0.1, basal breadth 0.01.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Definition.—Surface of the disk covered with radial spines. Bases of the marginal spines free, not connected by an equatorial girdle.

5. Astrosestrum acanthastrum, n. sp.

Disk with spiny surface, three times as broad as the outer and nine times as broad as the inner medullary shell. Pores subregular, circular; ten to eleven on the radius. Eight marginal spines (sometimes seven or nine) regularly disposed, triangular, about half as long as the radius of the disk, and one-third as broad at the base, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.18, of the outer medullary shell 0.06, of the inner 0.02; length of the radial spines 0.05, basal breadth 0.03.

Habitat.—North Atlantic, Gulf Stream, Færöe Channel, surface, John Murray.

6. Astrosestrum echinastrum, n. sp.

Disk with spiny surface, twice as broad as the outer and four times as broad as the inner medullary shell. Pores irregular, roundish; eight to nine on the radius. Eight marginal spines more or less regularly disposed, pyramidal, nearly as long as the radius of the disk, and not broader at the base than one large pore, without a connecting equatorial girdle.

Dimensions.—Diameter of the disk 0.15, of the outer medullary shell 0.07, of the inner 0.04; length of the radial spines 0.07, basal breadth 0.01.

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