Definition.—Astrolophida with thirty-two simple radial spines, regularly disposed within four meridian planes in such an order that their distal ends fall into five parallel zones. Central ends of the thirty-two spines supported one upon another in the centre of the spherical central capsule.
The genus Actinastrum differs from the two preceding genera in the definite number and order of the thirty-two radial spines, which are disposed in a very remarkable manner. Twenty radial spines are disposed after the Müllerian law of Icosacantha (compare above, p. [717]). The remaining twelve spines are four equatorial spines lying in the two secondary meridian planes, and eight tropical spines lying in the two primary meridian planes. We have therefore together eight equatorial, sixteen tropical, and eight polar spines (compare above, p. [729]).
1. Actinastrum legitimum, n. sp.
All thirty-two radial spines of equal size and similar form, cylindrical, conical at the distal end, at the central base pyramidal. Central capsule pellucid, colourless.
Dimensions.—Length of the radial spines 0.3, breadth 0.004.
Habitat.—South Pacific, Station 288, surface.
2. Actinastrum pentazonium, n. sp.
All thirty-two radial spines of equal size and similar form, compressed, two-edged, gradually becoming broader and thinner from the pyramidal central base towards the truncated distal end. Central capsule dark, opaque. (Compare the similar Chiastolus amphicopium, Pl. [129], fig. 3.)
Dimensions.—Length of the radial spines 0.2, breadth at the base 0.005, at the distal end 0.02.
Habitat.—South Pacific (west coast of Patagonia), Station 302, surface.