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



seven or nine) conical, half as long as the radius, twice as long as broad, without a connecting 

 equatorial girdle. 



Dimensions. Diameter of the disk 017, of the medullary shell 0'04 ; length of the radial spines 

 0-04, basal breadth 002. 



Habitat. Fossil in Barbados. 



7. Heliosestrum irregulare, n. sp. 



Disk with smooth surface, four times as broad as the medullary shell. Pores irregular, 

 roundish ; nine to eleven on the radius. Eight conical radial spines of irregular size and distribution, 

 often seven or nine, about as long as the radius of the disk (in some cases longer, in others shorter). 

 No connecting equatorial girdle. 



Dimensions. Diameter of the disk 02, of the medullary shell 005 ; length of the radial spines 

 01, basal breadth 0'02. 



Habitat. Central Pacific, 'Stations 270 to 272, depth 2425 to 2925 fathoms. 



Subgenus 2. Heliosestilla, Haeckel. 



Definition. Surface of the disk armed with radial spines. Bases of the marginal 

 spines free, without a connecting equatorial girdle. 



8. Heliosestrum octonum, u. sp. (PI. 34, fig. 3). 



Disk with spiny surface, three times as broad as the medullary shell. Pores circular, of very 

 different sizes ; eight to ten on the radius. Eight conical marginal spines of equal size and equi- 

 distant, as long as the radius of the disk, and one-third as broad at the base as the medullary shell. 

 Numerous spines on the surface bristle-shaped, on the margin half as long as the eight main spines, 

 in the central part shorter. 



Dimensions. Diameter of the disk 018, of the medullary shell O'OG ; length of the marginal 

 spines 01, basal breadth 0'02. 



Habitat. Central Pacific, Station 271, surface,. 



9. Heliosestrum cegineta, n. sp. 



Disk with spiny surface, four times as broad as the medullary shell. Pores irregular, roundish, 

 of different sizes ; twelve to fourteen on the radius. Eight pyramidal marginal spines regularly 

 disposed, four larger (perradial) alternating with four smaller (iuterradial) ; the former as long as 

 the radius of the disk, the latter half as long. 



Dimensions. Diameter of the disk 0'2, of the medullary shell 0'05 ; length of the marginal 

 spines 0'05 to 01, basal breadth 0'03. 



Habitat. South Atlantic. Station 330, surface. 



