2. _Dystympanium distephanus_, n. sp. Basal ring hexagonal, with six larger spines at the six corners, and numerous smaller ones between them. Mitral ring half as broad as the basal ring, also with six angular spines. The latter are connected with the former by six divergent curved columellæ, about as long as the diameter of the basal ring. Mitral lattice-plate flat, with irregular roundish pores. _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. {1008}Genus 435. _Parastephanus_, Haeckel, 1881, Prodromus, p. 446. _Definition._--#Tympanida# with two simple horizontal rings, connected by two vertical columellæ. The genus _Parastephanus_ is the simplest among the Eutympanida, and exhibits only two vertical rods or columellæ, which connect the two parallel horizontal rings. One of these latter must be regarded as the mitral or superior ring, the other as the basal or inferior ring; whilst the two parallel columellæ, connecting both, are the remaining vertical parts of the sagittal ring, the upper and lower parts of which are lost. By loss of the latter _Parastephanus_ has probably been derived from _Protympanium_. 1. _Parastephanus circularis_, n. sp. Two horizontal rings smooth, circular, of equal size, connected by two curved smooth columellæ, which are somewhat shorter than the diameter of the rings. _Dimensions._--Diameter of the rings 0.08, length of the columellæ 0.06. _Habitat._--Central Pacific, Station 263, depth 2650 fathoms. 2. _Parastephanus quadrispinus_, n. sp. (Pl. 93, fig. 21). Two horizontal rings smooth, elliptical or nearly circular, of equal size, connected by two vertical, slightly curved columellæ, which are about as long as the radius of the rings. Each ring bears two simple lateral spines, which in the mitral ring are curved downwards, in the basal ring upwards, possibly the last remains of a reduced frontal ring.