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



Proportion of the major axis of the ellipsoid to the minor = 5:4. Minor axis once and one r third as 

 broad as that of the ellipsoidal inner shell, the pores of which are also circular, but of half the size. 

 Two spines strong, three-sided pyramidal, acute, as broad as a large mesh, as long as the equatorial 

 axis. The stout inner prolongations of these form the only connection between the two shells. 



Dimensions. Longer axis of the ellipsoidal cortical shell 012, shorter axis 01 ; pores 0'02, 

 bars 0-002 longer axes of the ellipsoidal medullary shell 0'09, shorter axis 0'07 ; pores 001, 

 bars 0'002 ; length of the polar spines 01, basal breadth 0'002. 



Habitat. Central area of the Pacific, Station 272, depth 2600 fathoms. 



3. Lithatractus leptostylus, n. sp. 



Outer shell thin walled, smooth, with regular, circular pores of equal size, three to four times as 

 broad as the thin bars ; ten to twelve on the half equator. Proportion of the major axis to the 

 minor = 7 : '6. Minor axis three times as large as that of the inner spherical shell ; pores of the 

 latter half as large. Polar spines cylindrical, blunt, longer than the major axis, scarcely half as 

 broad as one larger pore. 



Dimensions. Longer axis of the cortical shell 014, shorter axis 012; pores 0'015 to 0'02, 

 bars 0'004 ; diameter of the medullary shell 0'04 ; length of the polar spines 015 to 0'2, its 

 thickness O'Ol. 



Habitat. Central area of the Pacific, Stations 270 to 272, depth 2425 to 2925 fathoms. 



4. Lithatractus pachy stylus, n. sp. 



Outer shell thick walled, smooth, with regular, circular pores of equal size ; twelve to fifteen on 

 the half equator. Each pore is deep, funnel-shaped, its outer aperture double the size of the inner, 

 its breadth about three times that of the high bars. Proportion of the major axis to the minor = 6 : 5. 

 Major axis double as long as the diameter of the spherical medullary shell. Polar spines very thick 

 and short, tetrahedral, one-fourth as long and broad as the major axis. 



Dimensions. Longer axis of the cortical shell 017, shorter axis 014; pores O'Ol, bars 0'003 : 

 diameter of the medullary shell 0'08 ; length and thickness of the polar spines 0'04. 



Habitat. Central area of the Pacific, Station 271, deptli 2425 fathoms. 



5. Lithatractus convallaria, n. sp. 



Outer shell thick walled, smooth, with elegant regular network ; the meshes circular, six-lobed, 

 rosette-like (of the same form as Stauroxiphos gladius, PI. 15, fig. 7 ), twice to three times as broad as 

 the bars ; six to eight on the half equator. Proportion of the major axis of the ellipsoid to the minor 

 = 4:3. Minor axis twice as long as the diameter of the inner spherical shell, which has regular, 

 simple, circular pores of half the size. Polar spines short and thick, conical, only one-fourth to 

 one-sixth as long as the minor axis, and quite as thick. 



Dimensions. Longer axis of the cortical shell 016, shorter axis 012 ; pores 0'016, bars 0'006 ; 

 diameter of the medullary shell 0'06 ; length of the polar spines 0'02 to 0'03, basal thickness the 

 same. 



Habitat. Central area of the Pacific, Station 268, depth 2900 fathoms. 



