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



1. Hexalonche phcenaxonia, n. sp. 



Cortical shell thin walled, smooth ; its pores regular, hexagonal, six to eight times as broad as 

 the bars ; eight to ten to twelve on the radius. Medullary shell one-third as broad, with 

 regular, hexagonal pores of half the size. Six spines triangular pyramidal, as long as the radius 

 of the shell, at the base as broad as one pore. (Differs from Hexastylus phccnaxonius, PI. 21, 

 fig. 3, only in the medullary shell and the six inner radial beams, connecting it with the 

 cortical shell.) 



Dimensions. Diameter of the outer shell 015, pores O'Ol to 0'015, bars 0'015 to 002 ; inner 

 shell 0-05 ; length of the spines 0'08, basal breadth' 0-01. 



Habitat. Central Pacific, Stations 266 to 271, depth 2425 to 2925' fathoms. 



2. Hexalonche rosetta, n. sp. (PI. 25, figs. 3, 3a, 3b). 



Cortical shell thick walled, smooth, two and a half times as broad as the medullary shell. 

 Pores of the latter (fig. 3) regular circular ; eight to ten on the half meridian, about as broad as 

 the bars between them. Pores of the outer shell regular, hexagonal, remarkable for a very 

 peculiar form and arrangement. In the transverse section of the shell (fig. 3Z>) they appear as 

 narrow, hexagonal prismatic canals, twice as high as broad, and four to five times as broad as 

 the thin elevated bars between them. Every seven meshes form together a larger, regular hexagon 

 (six pores surrounding one central pore). The periphery of these larger, rosette-like hexagons 

 projects more strongly from the surface than the walls between the smaller hexagons. On the half 

 meridian of the shell may be counted six to seven larger and eighteen to twenty smaller 

 hexagons. The six radial beams between the two shells are thin, three-sided prismatic, not 

 broader than the bars of the network, the prominent prolongations of which form six very strong 

 spines of peculiar club-like shape (fig. 3), as long as the radius of the outer shell. The three 

 wings of the club are lower in the inner, higher in the outer half ; the broadest part of the spine 

 (at the base and in the outer third) is as broad as a hexagonal rosette (equal to three meshes of 

 the outer shell) ; its outer apex is pyramidal. 



Dimensions. Diameter of the outer shell 0'13, pores O'OOS to O'Ol, bars 0'02 ; inner shell 

 0-05 ; length of the spines 0'07, distal breadth 0'03. 



Habitat. Tropical West Pacific, Station 225, depth 4475 fathoms. 



3. Hexalonche favosa, n. sp. 



Cortical shell thick walled, smooth, four times as broad as the medullary shell. Pores of the 

 former regular circular, hexagonally framed, deep funnel-shaped, of the same breadth as the bars ; 

 six to eight on the radius. Six spines triangular-pyramidal, as long as the radius, at the 

 base twice as broad as one pore. (Differs from the similar Hexastylus favosus mainly in the 

 possession of a medullary shell.) 



Dimensions. Diameter of the outer shell 0'16, pores and bars 0'012 ; inner shell 0'04; length 

 of the spines 0'08, basal breadth 0'025. 



Habitat. Equatorial Atlantic, Station 348, depth 2450 fathoms ; also fossil in Barbados. 



