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



4. Heliodiscus glyphodon, n. sp. (PL 35, fig. 2). 



Heliosestrum glyphodon, Haeckel, 1881, Prodromus et Atlas (pi. xxxv. fig. 2). 



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

 circular ; seven to eight on the radius. Marginal spines ten to twelve, equilateral triangular, flat, 

 deeply furrowed, twice as long as broad, and as long as the radius of the disk. 



Dimensions. Diameter of the disk 014, of the medullary shell 0'035 ; length of the radial 

 spines 0'07, basal breadth 0'035. 



Habitat. North Pacific, Station 253, depth 3125 fathoms. 



5. Heliodiscus helianthus, Haeckel. 



Haliomma helianthus, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxvii. 

 fig. 1. 



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

 disposed regularly in sixty to eighty radial series ; fourteen to sixteen on the radius. Marginal 

 spines sixty to eighty, conical, about as long as the diameter of the medullary shell, twice as 

 broad as one pore. 



Dimensions. Diameter of the disk 0'2, of the medullary shell 004; length of the radial 

 spines - 04, basal breadth O'OOS. 



Habitat. Fossil in Barbados. 



6. Heliodiscus sol, Haeckel. 



Haliomma sol, Ehrenberg., 1854, Mikrogeol., Taf. xix. fig. 52. 

 Heliodiscus sol, Haeekel, 1862, Monogr. d. Radiol., p. 438. 



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

 roundish ; eight to ten on the radius. Marginal spines twenty to thirty, conical, the largest as long 

 as the radius of the medullary shell, their bases widely distant. (The species from Barbados 

 figured by Ehrenberg, 1875, as Haliomma sol, appertains to Heliosestrum solare.) 



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

 spines 0'02 to 0'025, basal breadth O'Ol. 



Habitat. Fossil in Tertiar-y rocks of Greece (^Egina), Ehrenberg. 



7. Heliodiscus siculus, Stohr. 



Heliodiscus siculus, Stohr, 1880, Palseontogr., vol. xxvi. p. 89, Taf. i. fig. 14. 



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

 roundish ; seven to eight on the radius. Marginal spines forty to fifty, conical, very irregular, the 

 largest as long as the radius of the medullary shell, their bases coming in contact. 



Dimensions: Diameter of the disk 013 to 015, of the medullary shell 0'04 to 0'05 ; length of 

 the radial spines 0'02 to 0'03, basal breadth 0'002 to O'OOG. 



Habitat. Fossil in Tertiary rocks of Sicily, Grotte (Stohr), Caltanisetta (Teuscher). 



