REPORT ON THE RADIOLARIA. 319 



Dimensions. Major axis of the outer cortical shell 0'2, of the inner 015 ; equatorial axis of 

 the former 016, of the latter 012 ; diameter of the outer medullary shell - 06, of the inner 0'04 ; 

 pores of the cortical shells O'Ol to 0'02, of the medullary shells 0'004 to O'OOS, bars Of)03 to O'OOG ; 

 length of the radial spines 01, basal breadth 0'02. 



Habitat. Indian Antarctic Ocean, Station 157, depth 1950 fathoms. 



Genus 137. Lithatractus, 1 n. gen. 



Definition. Druppulida with simple ellipsoidal cortical shell and simple 

 medullary shell, with two large opposite polar spines in the main axis of equal size 

 and similar form. 



The genus Lithatractus, rich in common and widely distributed species, begins the 

 series of those Druppulida which are characterised by peculiar polar spines at both 

 poles of the main axis. It repeats the formation of Stylosphcera and Ellipsostylus, and 

 differs from the former in the ellipsoidal form of the cortical shell, from the latter in the 

 possession of a medullary shell. Formerly all these forms were united in the one genus 

 Stylosphcera (see above, p. 121). 



Subgenus 1. Lithatractara, Haeckel. 



Definition. Netw r ork of the outer shell regular or subregular, with meshes of 

 nearly equal size and similar form ; surface smooth, without thorns or papillae. 



1. Lithatractus hexagonalis, n. sp. 



Outer shell thin walled, smooth, without thorns or papillae, with regular delicate network ;. 

 the meshes hexagonal, three to four times as broad as the thin bars ; ten to twelve on the half 

 equator. Proportion of the major axis of the ellipsoid to the minor = 4:3. Minor axis three times 

 as large as that of the inner spherical shell ; pores of the latter, small, circular. Two spines three- 

 sided pyramidal, as long as the radius of the outer shell, each as broad at its base as one mesh. 



Dimensions. -Longer axis of the ellipsoidal cortical shell 016, shorter axis 012 ; pores - 011, 

 bars O'OOS ; diameter of the spherical medullary shell 0'04 ; length of the polar spines 0'07 ; basal 

 breadth O'Ol. 



Habitat. North Pacific, Station 253, depth 3125 fathoms. 



2. Lithatractus fragilis, n. sp. (PL 16, fig. 3). 



SI ylosphcera fragilis, Haeckel, 1881-, Prodromus et Atlus, pi. xvi. fig. 3. 



Outer shell thin walled, smooth, without thorns or papillae, with regular network ; the meshes 

 circular, of equal size, eight to ten times as broad as the thin bars ; six to eighf on the half equator. 



1 Lithatradus = Spindle of silex; x/tfo?, 



