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



3. Sethostaurus rhombostaurus, n. sp. (PI. 31, fig. 4). 



Disk with smooth surface, two and a half times as broad as the medullary shell. Pores 

 regular, circular ; ten to eleven on the radius. Margin simple, smooth, without girdle. Two 

 opposite spines longer than the diameter of the disk, four times as long as the two others, which 

 only equal its radius. Spines sword-shaped, angular. 



Dimensions. Diameter of the disk 0'14, of the medullary shell 0'06 ; length of the major 

 spines 0'2, of the minor 0'05, breadth 0'025. 



Habitat. North Atlantic, Station 353, depth 2965 fathoms. 



4. Sethostaurus recurvatus, n. sp. (PI. 31, fig. 3). 



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

 roundish ; eight to nine on the radius. Margin simple, smooth, without girdle. Four spines 

 cylindrical, irregularly curved, of different sizes ; one single very large, much longer than the three 

 others ; two opposite lateral spines recurved, hook -shaped. 



Dimensions. Diameter of the disk 0'15, of the medullary shell 0'05 ; length of the major spine 

 0'32, of the opposite spine 0'16, of both lateral spines 0'08. 



Habitat. South Pacific, Station 295, depth 1500 fathoms. 



Subgenus 2. Heliostaurus, Haeckel, 1881, Prodromus, p. 457. 



Definition. Margin of the disk with a solid equatorial girdle or a corona of 

 spines. 



5. Sethostaurus cruciatus, n. sp. (PI. 31, fig. 5). 



Heliostaurus cruciatus, Haeckel, 1881, Prodroinus et Atlas (pi. xxxi. fig. 5). 



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

 eleven to twelve on the radius. Margin with a solid, radially striped girdle, which bears on the 

 periphery forty to fifty triangular pointed teeth of unequal length. Four crossed spines of equal 

 size and similar form, pyramidal, sulcated, about as long as the radius of the disk, as broad at the 

 base as the girdle. 



Dimensions. Diameter of the disk 0'2, of the medullary shell 0'06 ; length of the crossed 

 spines 01, basal breadth 0'02. 



Habitat. Pacific, central area, Station 271, depth 2425 fathoms. 



6. Sethostaurus coronatus, n. sp. 



Disk with spiny surface, twice as broad as the medullary shell. Pores irregular, roundish ; 

 nine to ten on the radius. Margin of the disk with a solid broad girdle, bearing on the periphery 

 a corona of thirty to forty flat tongue-shaped teeth of different length. Four crossed spines 



