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



Dimensions. Diameter of the disk 0'16, of the medullary shell 0'05 ; length of the marginal 

 spines 0'03, basal breadth 0'002. 



Habitat. Mediterranean (south shore of France), J. Miiller. 



12. Heliodiscus echiniscus, n. sp (PL 34, fig. 5). 



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

 or polygonal; eight to ten on the radius. Marginal spines thirty to fifty, pyramidal, angular, of 

 very variable size, number, and disposition, gradually passing into the surface-spines; the largest 

 nearly as long as the diameter of the medullary shell. 



Dimensions. Diameter of the disk 014, of the medullary shell 0'045; length of the radial 

 spines 0'02 to 0'04, basal breadth 0'006. 



Habitat. Central Pacific, Station 272, depth 2600 fathoms. 



13. Heliodiscus pertusus, n. sp. (PI. 35, fig. 1). 



Heliosestrum pertusum, Haeckel, 1881, Prodromus et Atlas (pi. xxxv. fig. 1). 



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

 hexagonally framed; eight to ten on the radius. Marginal spines ten to thirty, very variable in 

 size and disposition ; commonly eight to twelve larger spines, which are pyramidal, about as long 

 as the radius of the disk, and perforated by two to four irregular, longish pores. Between these 

 fenestrated large spines are commonly ten to twenty smaller conical spines, gradually passing into 

 those of the surface. 



Dimensions. Diameter of the disk 013 to 016, of the medullary shell 0'04 to 0'05 ; length of 

 the marginal spines 0'04 to 0'08, basal breadth O'Ol to 0'015. 



Habitat. North Pacific, Stations 241 to 244, depths 2300 to 2900 fathoms. 



Subgenus 3. Heliodiscomma, Haeckel. 



Definition. Surface of the disk smooth, without radial spines. Bases of the 

 marginal spines connected by a solid equatorial girdle. 



14. Heliodiscus cingillum, n. sp. (PI. 33, fig. 7). 



Disk with smooth surface, five times as broad as the medullary shell. Pores regular, circular; 

 twelve to fourteen on the radius. Equatorial girdle about as broad as the medullary shell, in the 

 proximal half radially striped, on the margin with twenty to twenty-four short, flat, triangular spines, 

 which are shorter than the breadth of the girdle. 



Dimensions. Diameter of the disk 0'25, of the medullary shell 0'05; length of the marginal 

 spines 0'02, basal breadth 0'02. 



Habitat. Central Pacific, Station 274, depth 2750 fathoms. 



