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



Family XXXII. SOEEUMIDA, Haeckel (PL 49, figs. 12, 13). 

 Soreumida, Haeckel, 1881, Prodromus, p. 464. 



Definition. L arcoidea with quite irregular polythalamous shell, composed of 

 a variable number of chambers, aggregated without any definite order. Primordial 

 chamber either simple or Larnacilla-shaped. 



The family Soreumida contains a small number ofLarcoidea, different from 

 most other Sphserellaria in the complete irregularity of the polythalamous shell, 

 which is composed of a variable number of roundish chambers or subspherical 

 latticed shells, aggregated in the form of an irregular heap. We can distinguish in 

 this family only two genera, with very different structure of the central medullary 

 shell or the first chamber beginning the growth ; and these correspond to the two 

 subfamilies of the nearly allied Streblonida (p. 704). In Soreuma (as in Streblonia) 

 the first or primordial chamber, from which the growth begins, is like the 

 others, a simple spherical or irregular roundish lattice-shell. In Sorolarcus, however 

 (as in Streblopyle), the first or primordial chamber is a trizonal or Larnacilla-shell. 

 It is not improbable that the former originated phylogenetically from Streblonia, the 

 latter from Streblopyle, by loss of the original spiral order of growth. But it is 

 also possible that these groups have no nearer relation. Among the calcareous 

 Foraminifera a very similar form is represented by Acervulina and its allies. 



The general form of the whole shell in the Soreumida is sometimes more egg- 

 shaped or lentelliptical, at other times even subspherical, occasionally quite irregular, 

 tuberous, or clustered. The number of the aggregated chambers is very variable, in 

 Sorolarcns between ten and thirty, in Soretima ascending to fifty to eighty, sometimes 

 from one hundred to one hundred and fifty and more. Their size is sometimes nearly 

 equal, at other times very different, their form commonly very irregular, roundish, but 

 sometimes also subspherical or egg-shaped. The network of the shell is also commonly 

 irregular, with roundish pores of different sizes. The surface is usually smooth or rough, 

 rarely covered with radial spines. 



The central capsule is not known, as I observed only a few skeletons of this family. 



. Synopsis of the Genera of Soreumida. 



Primordial chamber of the shell simple, subspherical or roundish, . . .315. Soreuma. 



Primordial chamber of the shell trizonal or Larnacilla-shaped, . . . 316. Sorolarcug. 



Genus 315. Soreuma, 1 Haeckel, 1881, Prodromus, p. 464. 



.Dejinition. S oreumida with numerous chambers, aggregated without any 

 regularity around one simple, spherical or subspherical, central chamber. 



t, heap. 



