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



Subgenus 2. Heliodendrum, Haeekel. 

 Definition. — Surface of the disk armed with simple or l:)ranched radial spines. 



4. Heliodrymus setosus, n. sp. 



Disk with spiny surface, four times as broad as the medullary shell. Pores regular, circular ; 

 twelve to thirteen on the radius. Marginal spines ten to twelve, cylindrical, irregularly liranched, 

 each with two to eight Hexuose branches of different sizes ; tlie largest as long as the diameter of 

 the disk. Spines of tlie surface bristle-shaped, half as long, not Ijranched. 



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

 spines 0-12 to OlS, breadth 0-025. 



Habitat- — North Pacific, Station 254, surface. 



5. Heliodrymus ramosu.9, n. sp. (PI. 35, figs. 3, 4). 



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

 hexagoually framed; eleven to twelve on the radius. Marginal spines sixteen to twenty, cylindrical, 

 about as long as the radius, irregularly forked or branched, with unequal tlexuose branches. Spines 

 I if the surface nearly as long, bristle-shaped, also irregularly Ijranched. 



Dimensions. — Diameter of the disk 015, of the medullary shell 0'03 ; length of the spines O'OG 

 to 008, basal breadth 0-01 to 0-015. 



Habitat. — South Pacific, Station 288, surface. 



Ct. Heliodrymus viminalis, n. sp. (PI. 35, fig. 5). 



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

 roundish ; ten to twelve on the radius. Marginal spines fifteen to twenty, cylindro-conical, strong, 

 partly simple, partly forked, about as long as the diameter of the disk. Spines of the surface very 

 numerous, bristle-shaped, longer than the marginal spines, and more branched. 



Dimensions. — Diameter of the disk 0-15, of the medidlary shell O-OG ; length of the marginal 

 spines 0-11 to 0-14, basal breadth 0-01 to 0-015 ; length of tlie surface spines 0-2 to 0-03. 



Habitat. — Central Pacific, Station 271, surface. 



Genus 195. Astrophacus,^ Haeekel, 1881, Prodiomus, p. 457. 



Definition. — P h a c o d i s c i d a witli double 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 sjsines). 



The genus Astropliacus differs from the similar Heliodiscus in the duplication of 

 the medullary shell. The number and disposition of the radial spines of the margin 



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