Dimensions.—Diameter of the basal ring 0.1, mitral ring 0.05; length of the columellæ 0.09.
Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.
3. Dystympanium medusa, n. sp.
Basal ring circular, with eight larger and numerous smaller divergent spines. Mitral ring two-thirds as broad as the basal ring, octagonal, with eight conical ascending spines on the eight corners. The latter are connected with the former by eight divergent, curved columellæ, as long as the diameter of the mitral ring. Mitral lattice-plate nearly hemispherical, with nine circular pores (eight peripheral pores around one central pore).
Dimensions.—Diameter of the basal ring 0.12, mitral ring 0.08; length of the columellæ 0.09.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
Subfamily 4. Eutympanida, Haeckel.
Definition.—Tympanida with two simple horizontal rings, which are connected by a variable number of vertical rods or columellæ. Therefore the shell exhibits a large simple mitral gate on the upper, and a large simple basal gate on the lower side; between the two a variable number of lateral gates.
Genus 435. Parastephanus, Haeckel, 1881, Prodromus, p. 446.
Definition.—Tympanida with two simple horizontal rings, connected by two vertical columellæ.