Page:Scientific results HMS Challenger vol 18 part 1.djvu/763

Rh 9. Myelastrum ciliatum, n. sp.

Anterior arms trifid, with two shallow incisions. Posterior arms somewhat smaller, also trifid, with two deeper incisions. Sagittal constriction a little larger than the transverse. Margin of the disk ciliated, with radial bristle-shaped spines, as prolongations of the inner radial beams, arising from the central disk.

Dimensions.—Radius of the anterior arms 0.6, of the posterior 0.5; longitudinal constriction 0.4, transverse 0.35.

Habitat.—South Pacific, Station 288, surface.

10. Myelastrum lobatum, n. sp.

Anterior arms somewhat broader but shorter than the posterior arms. Each arm four-lobed, with three terminal shallow incisions of nearly equal size. Sagittal constriction smaller than the transverse. Surface of the disk bristly.

Dimensions.—Radius of the anterior arms 0.4, of the posterior 0.5; longitudinal constriction 0.3, transverse 0.35.

Habitat.—North Pacific, Station 253, surface.

11. Myelastrum rotula, n. sp.

Anterior arms little broader than the posterior, but of the same length. Each arm four-lobed, with three terminal deep incisions of equal size. Sagittal and transverse constrictions equal. The whole disk nearly circular, resembles a wheel with sixteen spokes. Surface smooth.

Dimensions.—Radius of all four arms 0.5; longitudinal and transverse constrictions 0.3.

Habitat.—Pacific, central area, Station 274, surface.

12. Myelastrum giganteum, n. sp.

Anterior arms somewhat broader and shorter than the posterior. Each arm four-lobed, with three shallow terminal incisions, the middle incision twice as deep as the two laterals. Sagittal constriction a little larger than the transverse. Margin ciliated, with radial bristle-shaped spines as prolongations of the inner radial beams, proceeding from the central disk (as in Myelastrum dodecaceros, Pl. 47, figs. 11, 11a).

Dimensions.—Radius of the anterior arms 0.6, of the posterior 0.8; longitudinal constriction 0.6, transverse 0.5.

Habitat.—Pacific, central area, Station 271, surface.