REPORT ON THE RADIOLARIA. 713 



The genus Soreuma contains those Soreumida in which no trace of any regular 

 structure is found, but all the chambers of the irregular shell are without any order, 

 aggregated around a simple spherical or subspherical central chamber or medullary shell. 

 Soreuma may have originated either from Sorolarcus by loss of the central Larnacilla-shell 

 or from Cenolarcus by irregular apposition of new chambers around the lentelliptical 

 central chamber or simple Larcoid-shell. Some species seem to exhibit a transition to 

 Sorolarcus. Owing to the absolute irregularity of the polythalamous shell Soreuma 

 resembles Acervulina among the Foraminifera. 



Subgenus 1. Soreumium, Haeckel. 

 Definition. Shell without radial spines. 



1. Soreuma irregulare, n. sp. (PI. 49, fig. 12). 



Shell irregular, clustered, or tuberous, composed of a large number (one hundred and twenty to 

 one hundred and fifty or more) of irregular, roundish chambers of very different sizes, the largest 

 four to five times as broad as the smallest. Network very delicate, with very small roundish pores, 

 to five times as broad as the bars. Surface thorny. 



Dimensions. Diameter of the shell O3, of the single chambers 0'02 to 0'08. 



Habitat. North Pacific, Station 244, depth 2900 fathoms. 



2. Soreuma acinosum, n. sp. 



Shell irregularly lentelliptical, with different growth in the three dimensions, composed of 

 a large number (forty to sixty or more) of irregular, roundish chambers of very different 

 sizes, the largest six to eight times as broad as the smallest. Pores subregular, circular, twice as 

 broad as the bars. Surface smooth. 



Dimensions. Length of the shell 0'21, breadth O'l7, height 0'13 ; diameter of the largest 

 chambers 0'03, of the smallest 0'004. 



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



3. Soreuma subglobosum, n. sp. 



Shell nearly spherical, composed of a variable number (twelve to fifteen or more) of irregularly 

 aggregated stibspherical chambers of nearly equal size. Pores subregular, circular, twice as broad 

 as the bars. Surface thorny. 



Dimensions. Diameter of the shell 0'25, of the largest chambers 0'04, of the smallest 0'005. 



Habitat. Pacific, central area, Station 266, depth 2750 fathoms. 



(ZOOL. CHALL. EXP. PART XL. 1885.) Rr 90 



