_Dimensions._--Shell 0.14 long, 0.15 broad. _Habitat._--South Atlantic, Station 332, depth 2200 fathoms. 2. _Tridictyopus conulus_, n. sp. (Pl. 51, fig. 7). Shell campanulate conical, about one and a half times as long as broad (excluding horn and feet). Pores mostly triangular, disposed in subregular hexagonal figures, which are separated by bands of smaller irregular polygonal pores. Horn short and stout, three-sided pyramidal. Three feet triangular shovel-shaped, convergent, about one-sixth as long as the shell. _Dimensions._--Shell 0.3 long, 0.2 broad; horn 0.04 long, feet 0.05 long. _Habitat._--Equatorial Atlantic, Station 347, depth 2250 fathoms. 3. _Tridictyopus elegans_, R. Hertwig. _Tridictyopus elegans_, R. Hertwig, 1879, Organismus d. Radiol., p. 75, Taf. vii. fig. 3, 3_a_, 3_b._ Shell slender, conical, campanulate, about twice as long as broad (excluding horn and feet). Most pores subregular triangular, with some irregular polygonal ones intermingled. The horn in the two observed specimens was broken off, together with the conical apex of the shell. Three feet triangular shovel-shaped, about one-sixth as long as the shell. _Dimensions._--Shell 0.3 long, 0.15 broad; feet 0.05 long. _Habitat._--Mediterranean (Messina), R. Hertwig, surface. {1146}Subfamily 2. ARCHIPERIDA, Haeckel, 1881, p. 429. _Definition._--#Tripocalpida# with the basal mouth of the shell fenestrated (vel Monocyrtida triradiata clausa). Genus 504. _Euscenium_,[121] n. gen. _Definition._--#Archiperida# (vel Monocyrtida triradiata clausa) with a free simple internal columella, prolonged into an apical horn. Three basal feet free, without lateral wings. The genus _Euscenium_ and the three following nearly allied genera form together the remarkable small group of Euscenida, probably one of the oldest and most primitive of all #Cyrtoidea#, and perhaps the common root of this suborder, arising directly from the #Plectoidea#. The simple skeleton is composed of four radial beams united in one point (the cortinar centrum). Three beams are directed downwards, and form three divergent basal feet; the fourth beam is directed upwards and represents an apical horn; its basal part is enclosed as "columella" in the cavity of the simple shell, the lattice-work of which connects the four spines (compare above, _Plectaniscus_, p. 924). In the genus _Euscenium_, the simplest of all, the columella is simple, and the three feet also simple, without wings. Subgenus 1. _Euscenarium_, Haeckel. _Definition._--Three feet simple, not branched. 1. _Euscenium plectaniscus_ (Pl. 98, fig. 1).