Page:Scientific results HMS Challenger vol 18 part 1.djvu/939

Rh Actinastrum pentazonium (p. 733) and of Chiastolus amphicopium (Pl. 129, fig. 3), but much more numerous, smaller, and not regularly disposed. These latter two Actinelida must be separated on account of the regular disposition of the thirty-two spines.

Dimensions.—Length of the spines 0.2, basal breadth 0.008, distal breadth 0.02.

Habitat.—South Pacific, Station 165, surface.

Definition.—Radial spines quadrangular, prismatic, or pyramidal, their transverse section square.

4. Actinelius pallidus, Haeckel.

Actinelius pallidus, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 364.

Spines eighty to one hundred and twenty or more, quadrangular, prismatic, of equal breadth throughout their whole length. Apex simple, truncate or pyramidal. Base a four-sided slender pyramid. Central capsule pale yellowish. Granules of the sarcode colourless.

Dimensions.—Length of the spines 0.2 to 0.3, breadth 0.005.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific.

5. Actinelius polyacanthus, n. sp.

Spines two hundred to three hundred or more, quadrangular, pyramidal, gradually thinned towards the simple apex. Base a small three-sided pyramid. Central capsule opaque.

Dimensions.—Length of the spines 0.12 to 0.18, basal breadth 0.012.

Habitat.—South Pacific, Station 291, surface.

Definition.— with a variable and undetermined number of simple radial spines of different sizes (large and small spines intermingled), which are united in the centre of the spherical central capsule.

The genus Astrolophus differs from the nearly allied ancestral genus Actinelius only in the unequal size of the numerous radial spines. In both observed species very numerous small spines are intermingled with a small number of large spines, and between them numerous spines of medium size. The small spines fill up the hollow spaces between the basal parts of the large spines.