240 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus 95. Heliosoma,^ Hcaeckel, 1881, Prodromus, p. 452. 



Definition. — Astrosph serida with one medullary (intracapsular) and one cortical 

 (extracapsidar) shell, the two l)eing connected by radial beams piercing the central capsule. 

 Shell surface covered with simple radial spines of two different kinds ; larger main spines 

 and smaller by-spines. 



The genus Heliosoma differs from the preceding Ilaliomma in the possession of 

 two different kinds of radial spines, and exhibits therefore the same relation to it that 

 Heliosphmra bears to AcanthospJmra among the Coscinommida. The smaller by- 

 spines are much more numerous than the larger main spines. 



Subo-enus 1. Heliosomantha, Haeckel. 

 Definition. — -Pores of the cortical shell regular, of nearly equal size and similar form. 



1. Heliosoma radians, n. sp. (PI. 28, figs. 3, 3a). 



Cortical sliell very thiu walled, with thread-like hais and regular, hexagonal meshes ; twenty to 

 twenty-two on the radius. Medullary shell only one-fifth as large, of the same structure. The two 

 shells connected by twenty very thin radial beams, which are prolonged outside into twenty stout, three- 

 sided pyramidal main spines, as long as the diameter of the inner shell. Between these, arising from 

 the surface, numerous bristle-shaped by-spines. 



I)imensions. — Diameter of the outer shell 0-25, inner 0-05, pores 0-012 ; length of the main 

 spines 0-05, basal breadth 0'012. 



Habitat — Central Pacific, Stations 26G to 274, surface. 



2. Heliosoma elegans, n. sp. 



Cortical shell thick waUed, with regular, circular, hexagonally framed pores, twice as broad as 

 the bars ; ten to twelve on the radius. Medullary shell half as large, with simple, regular, circular 

 pores, twice as broad as the bars. The two shells connected by twenty very thin radial beams, which 

 are prolonged outside into twenty slender, three-sided pyramidal main spines as long as the radius. 

 In each corner of the surface hexagons a bristle-shaped by-spine one-fourth as long. 



Dimensions. — Diameter of the outer shell 0-12, inner O'OG ; outer pores 0-006, bars 0-00.3 ; length 

 of the main sphies 0-05, basal breadth OOL 



Habitat. — Central Pacific, Station 271, surface. 



3. Heliosoma echinaster, Haeckel. 



Haliomma echinaster, Haeckel, 1862, Monogr. d. Radio]., p. 429, Taf. x.xiv. figs. 1-3. 

 Cortical shell thin walled, with regular, circular, hexagonally framed pores, twice as broad as the 

 bars ; ten to twelve on the radius. Medullary shell one-fourtli as large, with few irregular, large, 



1 Hdiosoma='S)UD.-\oA.j ; "a;o{, nSf^ct. 



