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



2. Spironium diagonale, n. sp. 



Cortical shell nearly spherical, four times as great as the subspherical medullary shell. Surface 

 rough. The spiral wings of the transverse girdle about half as broad as the eight internal gates 

 between them and the axial beams. 



Dimensions. Diameter of the cortical shell O16, of the medullary shell 0'04. 



Habitat. Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms. 



Subgenus 2. Spironilla, Haeckel. 

 Definition. Surface of the shell covered with simple or branched radial spines. 



3. Spironium spinosum, n. sp. 



Cortical shell subspherical, five times as great as the subspherical medullary shell. Surface 

 covered with numerous (sixty to eighty or more) simple, bristle-like radial spines, longer than the 

 shell. The spiral wings of the transverse girdle of about the same breadth as the eight internal 

 gates between them and the axial beams. 



Dimensions. Diameter of the cortical shell 0'2, of the medullary shell 0'04. 



Habitat. Pacific, central area, Station 274, surface. 



4. Spironium arbustum, n. sp. 



Cortical shell lentelliptical, its breadth surpassing its length considerably. Surface covered 

 with numerous (forty to sixty or more) thin radial spines, about as long as the greatest diameter of 

 the shell ; each spine with two to six lateral branches, which are either simple or again branched 

 (similar to Cromyodrymus abietinus, PI. 30, fig. 6). The spiral wings of the transverse girdle 

 only half as broad as the eight internal gates between them and the strong beams of the 

 principal axis. 



Dimensions. Length of the cortical shell 0'12, breadth 015 ; length of the hexagonal medullary 

 shell 0'05, breadth 0'04. 



Habitat. Pacific, central area, Station 271, depth 2425 fathoms. 



Family XXX. STKEBLONIDA, n. fam. (PI. 49, figs. 8, 9). 



Definition. L arcoidea with asymmetrical, spiral, polythalamous shell, composed 

 of a variable number of roundish chambers, which form together an ascending spiral ; 

 both halves of the shell unequal. Primordial chamber either simple or Larnacilla- 

 shaped. 



The family Streblonida comprises those L a r c o i d e a in which a number of 

 chambers is arranged in an ascending spiral, round a simple or trizonal primordial 

 chamber, like winding stairs. They show the same spiral structure as in the foregoing 



