REPORT ON THE RADIOLARIA. 701 



Genus 309. Spirom\im,^ n. gen. 



Definition. — L i t li e 1 i cl a with douljle, trizonal or Larnacilla-sh.a:peil medullary shell ; 

 cortical shell subspherical or lentelliptical, constructed of two crossed spirals, which arise 

 from both lateral wings of one girdle (ctommonly the lateral girdle) and revolve in 

 an opposite diagonal direction around the principal axis. 



The genus Spironium differs in a very remarkable manner from all foregoing 

 Lithelida, and is distinguished by a quite peculiar mode of growth. It is most nearly 

 allied to Larcopyle, and may, like this, he derived from Amphipyle (or rather from 

 Larnacilla, beginning to transform into Amphipyle). But whilst in Larcopyle one of 

 the two wings of the lateral girdle overgrows the other in the direction of the transverse 

 axis (turning around the principal axis), here in Spironium both lateral wings begin at 

 the same time to grow out from the lateral sides of the Zor?iaci7Za-shaped medullary 

 shell ; the most remarkable thing is, however, that the direction of growth in the wings 

 is diverse from the beginning : the left wdng grows downwards and turns around the 

 lower (aboral) pole of the principal axis, the right wing grows upwards and turns around 

 the upper (oral) pole of the same axis. Thus both wings of the lateral girdle are crossed 

 in diagonal axes, and with increasing growth one overgrows the other in the direction of 

 these diagonals, so as to resemble the figure 8 in shape. The open gates remaining 

 between the turnings of the girdle become afterwards closed on the surface by irregular 

 lattice-work, and so the whole cortical shell assumes finally a spherical, ellipsoidal, or len- 

 telliptical form. Its surface sometimes becomes covered with simple or branched radial 

 spines. In the interior the eight characteristic egg-shaped gates of Octopyle are com- 

 monly (or constantly ?) visible, two strong radial beams in the principal axis arising from 

 the poles of the lentelliptical medullary shell. 



Subgenus 1. Spironetta, Haeckel. 

 Definition. — Surface of the sheU smooth or rough, Init not with radial spines. 



1. Spironium octonium, n. sp. (PI. 49, fig. 7). 



Cortical shell lentelliptical, its breadth (or transverse axis) surpassing considerably the length 

 (or the principal axis). Surface thorny and somewhat hump-backed. The spiral wings of the 

 transverse girdle have about the same breadth as the eight internal gates between them and the 

 axial beams. 



Dimensions. — Length of the cortical shell (or principal axis) (J'15, breadth (or transverse axis) 

 0-2 ; length of the medullary shell 0'05, breadth 0-04. 



Habitat. — South Atlantic, west of Tristan da Cunha, Station 332, depth 2200 fathoms. 



' /Sp»VomMm = Shell with spiral structure ; nirufmiaii. 



