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



6. Amphitholus armatus, n. sp. 



Central chamber twice as broad, but of the same height, as the Hat vaulted cupolas. Surface 

 armed with thirty to forty very large three-sided prismatic spines, longer than the major axis of 

 the shell. Pores irregular, roundish, twice to five times as broad as the bars ; eight to nine on the 

 basal semicircle of one cupola. 



Dimensions. Major axis of the shell 015, minor axis O'l ; pores 0'006 to 0'015, bars 0'003 ; 

 length of the spines 0'2 to 0'25, breadth O'Ol. 



Habitat. North Atlantic, Station 353, surface. 



7. A mphitholus polyacanthus, n. sp. 



Central chamber of the same breadth and height as both cupolas. Surface armed with very 

 numerous (sixty to eighty) strong conical spines, about as long as the minor axis of the shell. 

 Pores subregular, circular, twice as broad as the bars ; sixteen to eighteen in the basal semi- 

 circle of on'e cupola. 



Dimensions. Major axis of the shell 013, minor 0'08 ; pores O'OOG, bars 0'003 ; length of the 

 radial spines 0'09, breadth 0'006. 



Habitat. South Atlantic, Station 332, depth 2200 fathoms. 



8. Amphitholus panicium, n. sp. (PL 10, fig. 4). 



Central chamber ellipsoidal, nearly twice as broad, but of the same height, as both cupolas. 

 Whole surface thorny; the largest radial thorns about as long as the medullary shell. Pores 

 irregular, roundish, twice to four times as broad as the bars. On the base of each cupola a circle 

 of ten to twelve larger square pores, separated by radial beams, which are prolonged into stouter 

 free spines. This remarkable formation of the cupolas, very rare in this family, recalls the 

 characteristic formation of the distal chambers of the Panartida and Zygartida (e.g., PI. 40, 

 figs. 4, 8, &c.), where it is very common. 



Dimensions. Major axis of the shell 015, minor 01 ; pores O'OOS to 0'012, bars 0'003 ; large 

 square pores 0'02 ; axes of the medullary shell 0'03 and 0'02. 



Habitat. Indian Ocean, Madagascar, Rabbe, surface. 



Genus 292. Amphitholonium, 1 n. gen. 



Definition. T holonida with double cortical shell (with external veil), with 

 two hemispherical cupolas, opposite on the poles of one axis ; central chamber (between 

 them) Larnacilla -shaped, with medullary shell. 



The genus Amphitholonium differs from the nearly allied Amphitholus (probably 

 its ancestral form) only in the duplication of the cortical shell ; the outer has the 



1 Amphitholonium = Small shell with two opposite cupolas ; */*<?>!, irihuvtov. 



