730 THE VOYAGE OF H.M.8. CHALLENGER. 



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The genus Actinelius comprises the most simple and primitive forms among all 

 ACANTHARJA, and may be regarded as the common ancestral stock of this whole legion. 

 The spherical central capsule is pierced by numerous simple radial spines of equal size, 

 the pyramidal bases of which are supported one upon another with their triangular 

 faces in the centre of the capsule. The number and position of the spines are quite 

 indefinite and variable. We may derive Actinelius either from Actissa (Colloidea) 

 by development of acanthinic radial spines, or directly from Actinosphcerium, 

 (Heliozoa) by formation of a central capsule. 



Subgenus 1. Actinelarium, Haeckel. 



Definition. Radial spines cylindrical, conical, or spindle-shaped, their transverse 

 section circular. 



1. Actinelius primordialis, n. sp. (PI. 129, fig. 1). 



Spines sixty to eighty or more, cylindrical, at the distal end thickened, spindle-shaped. Apex 

 simple. Base a small slender pyramid. Central capsule yellow. Granules of the sarcode 

 colourless. 



Dimensions. Length of the spines 0'3 to 0'4, breadth in the distal part 0'02, in the basal 

 part 0-008. 



Habitat. Central Pacific, Stations 265 to- 274, surface. 



2. Actinelius purpureus, Haeckel. 



Actinelius purpureus, Haeckel, 1865, Zeitsclir. f. wiss. Zool., Ed. xv. p. 364, Taf. xxvi. fig. 4. 



Spines thirty to forty or more, cylindrical, very thin, a little thinner towards both ends. 

 Apex simple. Base a small sulcate pyramid. Central capsule opaque, purple. Granules of 

 the sarcode also purple. 



Dimensions. Length of the spines - 2 to 0'3, breadth 0'002. 



Habitat. Mediterranean (Nice), Haeckel. 



Subgenus 2. Actinelidium, Haeckel. 



Definition. Radial spines compressed, two-edged ; their transverse section elliptical 

 or lanceolate. 



3. Actinelius protogenes, n. sp. 



Spines fifty to sixty, compressed, two-edged, gradually broadened towards the truncated distal 

 end. Basal or proximal end thin, pyramidal. The spines of this species are similar to those of 



