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



Subgenus 3. Astrosestomma, Haeckel. 



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

 marginal spines connected by a solid equatorial girdle. 



7. Astrosestrum pelagia, n. sp. 



Disk with smooth surface, three times as broad as the outer and eight times as broad as the 

 inner medullary shell. Pores regular, circular ; eight to nine on the radius. Eight marginal spines 

 conical, about as long as the radius of the disk, of nearly equal length, one-third as broad at the 

 base, connected by a radially striped equatorial girdle. 



Dimensions. — Diameter of the disk 018, of the outer meduUary shell 0-06, of the inner 0-023 ; 

 length of the radial spines 0'09, basal breadth 0-03. 



Habitat. — Indian Ocean, Ceylon, Haeckel, surface. 



8. Astrosestrum Jioscula, n. sp. 



Disk with smooth surface, two and a half times as broad as the outer and five times as broad 

 as the inner medullary shell. Pores irregular, roundish ; ten to eleven on the radius. Eight 

 marginal spines triangular, plain, scarcely half as long as the radius of the disk, nearly as broad at 

 the base, connected by an even equatorial girdle. 



Dimensions. — Diameter of the disk 0'2, of the outer meduUary shell 008, of the inner 0'04 ; 

 length of the radial spines 0'09, basal breadth 0'07. 



Habitat. — South Atlantic, Station 325, surface. 



Subfamily 3. Heliodiscida, Haeckel, 1881, Prodromus, p. 457. 



Definition. — P hacodiscida with a variable number of radial sj^ines on the 

 margin of the disk (ten to twenty or more), which are commonly more or less irregular 

 (sometimes regularly formed and disposed). 



Genus 193. Heliodiscus,^ Haeckel, 1862, Monogr. d. EadioL, p. 436. 



Definition. — P hacodiscida with simple medullary shell and with numerous 

 (ten to twenty or more) simple radial spines on the margin of the disk (commonly 

 with a variable number and an irregular disposition of the undivided spines). 



The genus Heliodiscus, the most common and polymorphic of all Phacodiscida, 

 was founded by me in 1862 as the first known type of this family {loc. cit.). I use 



