Shell ovate, thorny, with large roundish pores, which are closed by sieve-plates with numerous small porules. Basal plate with two pairs of simple large pores (two smaller jugular and two larger cardinal, similar to Pl. 98, fig. 10_b_). Two horns divergent, curved, slender, pyramidal; the apical horn longer than the shell, the frontal horn shorter. Three feet divergent, longer than the shell, three-sided prismatic, at the distal end club-shaped, thorny. _Dimensions._--Shell 0.1 long, 0.08 broad; horns and feet 0.11 to 0.14 long. _Habitat._--Tropical Pacific, Station 225, depth 4475 fathoms. 2. _Archipera pentacantha_, n. sp. Shell pear-shaped, smooth, with numerous and small irregular roundish pores. Basal plate with three larger pores. Two horns and three feet of nearly equal size and similar form, three-sided {1156}prismatic, about as long as the shell diameter, somewhat curved. The apical horn stands on the apex, the frontal horn half-way up the shell. _Dimensions._--Shell 0.08 long, 0.06 broad; horns and feet 0.05 to 0.07 long. _Habitat._--Central Pacific, Station 272, depth 2600 fathoms. 3. _Archipera bicornis_, n. sp. Shell ovate, rough, with small regular circular, sparsely scattered pores. Basal plate with four larger central and a peripheral coronal of twelve smaller pores. Two horns near the apex widely divergent, somewhat shorter than the shell, of equal size and similar form. Three feet twice as long, horizontally expanded. All five spines slender, three-sided pyramidal, straight. _Dimensions._--Shell 0.07 long, 0.06 broad; horns 0.05 long, feet 0.1 long. _Habitat._--Central Pacific, Station 271, depth 2425 fathoms. 4. _Archipera tricornis_, n. sp. Shell subspherical, smooth, with subregular circular pores. Basal plate with four large meshes (two major cardinal and two minor jugular pores). On the apex three divergent pyramidal horns of different size, one larger occipital and two smaller frontal horns. Three feet prismatic, about twice as long as the shell. _Dimensions._--Shell diameter 0.05, length of the feet 0.1. _Habitat._--North Pacific, Station 253, depth 3125 fathoms. 5. _Archipera quadricornis_, n. sp. Shell ovate, smooth, with a small number of irregular roundish, widely scattered pores. Basal plate with four crossed meshes of nearly equal size. On the equator there arise four divergent prismatic horns of nearly equal size, three of which correspond to the three feet, whilst the fourth is opposite to the caudal foot. The three feet are also prismatic, as long as the shell, horizontally expanded. (Similar to the upper half of _Lithomelissa decacantha_, Pl. 56, fig. 2, but without thorax.) _Dimensions._--Shell 0.05 long, 0.04 broad; horns and feet 0.06 long. _Habitat._--South Pacific, Station 300, depth 1375 fathoms. 6. _Archipera multicornis_, n. sp.