Dimensions.—Major axis 0.17, minor 0.14; pores and bars 0.003 to 0.009; length of the radial spines 0.08; diameter of the medullary shell 0.09.
Habitat.—Fossil in the Tertiary rocks of the Nicobars, Haeckel.
Genus 133. Prunulum,[[172]] n. gen.
Definition.—Druppulida with simple ellipsoidal cortical shell and double medullary shell; without spines or polar tubes.
The genus Prunulum differs from Druppula in the double (not simple) medullary shell, which is sometimes spherical, sometimes ellipsoidal; it may be derived either from Druppula by duplication of the medullary shell, or from Thecosphæra by prolongation of one axis.
Subgenus 1. Prunuletta, Haeckel.
Definition.—Network of the cortical shell regular, with meshes of equal size and similar form.
1. Prunulum frugulum, n. sp.
Cortical shell thin walled, smooth, with regular, hexagonal pores, three times as broad as the bars; ten to twelve on the half equator. Proportion of the major axis of the ellipsoid to the minor = 4 : 3. Both medullary shells spherical. (Differs from Druppula drupa almost entirely in the double medullary shell.)
Dimensions.—Major axis of the ellipsoidal cortical shell 0.12, minor 0.09; pores 0.006, bars 0.002; diameter of both medullary shells 0.05 and 0.03.