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



Dimensions. Diameter of the disk O2 to O25 ; length of the radial spines 0'005 to O'OIS, basal 

 breadth O'OOl to 0'003. 



Habitat. Pacific, central area, Stations 266 to 268, surface; fossil in Barbados and Sicily. 



3. Stylotrochus helianthus, n. sp. 



Spongy framework of the whole disk irregular. Thirty to fifty very large, conical radial spines, 

 about as long as the diameter of the disk, and at the base two to four times as broad as one mesh 

 of the framework (without internal prolongations). 



Dimensions. Diameter of the disk 0'15 to 0'2 ; length of the radial spines - 16 to 0'24, basal 

 breadth O'OOS to 0-016. 



Habitat. Pacific, central area, Station 272, surface. 



4. Stylotrochus rhabdostylus, Haeckel. 



Spongosphiera rhabdostyla, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 256, 

 Taf. xxvi. figs. 1, 2. 



Spongy framework of the whole disk irregular. Four very large marginal primary spines 

 crossed in two equatorial diameters, perpendicular one to another, and between them numerous 

 (twelve to twenty or more) smaller secondary spines. The latter arise from the margin, whilst the 

 former pierce the disk and are nearly united in its centre. All the spines are cylindrical, the 

 smaller as broad as one mesh, the larger three to six times as broad. 



Dimensions. Diameter of the disk 0'2 ; length of the four main spines 015 to 0'3, breadth O'Ol 

 to 0'02 ; length of the accessory spines 0'05 to O'l, breadth O'OOS. 



Habitat. Fossil in the rocks of Barbados. 



5. Stylotrochus heter acanthus, Haeckel. 



Spongotroclius heteracanthuti, Haeckel, 1862, Monogr. d. Radiol., p. 464. 



Spongy framework of the whole disk irregular. Ten very long needle-shaped marginal spines 

 (symmetrically distributed), and between them numerous very fine, shorter, accessory, bristle- 

 shaped spines. 



Dimensions. Diameter of the disk 016 ; length of the main spines 016, basal breadth 0'002 ; 

 length of the secondary spines 0'03. 



Habitat. Mediterranean (Messina), surface. 



Subgenus 2. Stylospongia, Haeckel, 1862, Monogr. d. Radiol., p. 473. 



Definition. Spongy framework of the disk in the inner part with concentric rings 

 or spiral convolutions, in the outer part quite irregular. 



