Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
3. Spongophortis larnacilla, n. sp. (Pl. [49], figs. 11a-11d).
Cortical shell irregular, roundish, tuberous, three to four times as large as the enclosed lentelliptical Larnacilla-shell, connected with it by two opposite latticed wings (the halves of the transverse girdle of Tetrapyle). Spongy framework compact, about half as thick as the medullary shell. Surface rough. (May be regarded as an abnormal Tetrapyle or Larnacalpis, with an irregular spongy cortical shell.)
Dimensions.—Diameter of the spongy cortical shell 0.16 to 0.2, of the trizonal medullary shell 0.04 to 0.06.
Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.
Family XXXII. Soreumida, Haeckel (Pl. [49], figs. 12, 13).
Soreumida, Haeckel, 1881, Prodromus, p. 464.
Definition.—Larcoidea 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 of Larcoidea, different from most other Sphærellaria 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 Sorolarcus between ten and thirty, in Soreuma 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.