_Definition._--Feet spiny or branched. 4. _Peridium spinipes_, n. sp. (Pl. 53, fig. 9). Shell ovate, rough or thorny, with irregular roundish pores. Basal plate with four pores (two larger cardinal and two smaller jugular pores). Horn oblique, occipital, three-sided pyramidal, half as long as the shell, connected with the caudal foot by a prominent crest. Three feet horizontally expanded, prismatic, spiny, about as long as the shell. _Dimensions._--Shell 0.08 long, 0.06 broad; horn 0.04 long, feet 0.06 to 0.09 long. _Habitat._--Central Pacific, Station 266, depth 2750 fathoms. 5. _Peridium palmipes_, n. sp. (Pl. 53, fig. 10). Shell ovate, smooth, with irregular roundish pores. Basal plate with three large pores. Horn oblique, three-sided pyramidal, about as long as the shell, inserted near its occipital base. Three feet prismatic, slender, half as long, ending with a broad dentate plate. _Dimensions._--Shell 0.06 long, 0.05 broad; horn 0.05 long, feet 0.03 long. _Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms. {1155}6. _Peridium alatum_, n. sp. (Pl. 97, fig. 7). Shell subspherical smooth, with regular circular, hexagonally-framed pores. Basal plate with nine pores (three larger central and six smaller distal pores). Horn apical, of equal size and the same form as the three feet, three-sided prismatic, with three broad prominent wings, somewhat longer than the shell. _Dimensions._--Shell 0.07 long, 0.08 broad; horn and feet 0.1 to 0.12 long. _Habitat._--Central Pacific, Station 272, depth 2600 fathoms. 7. _Peridium cervinum_, n. sp. Shell subspherical, spiny, with subregular circular pores. Basal plate with four pores (?). Horn apical, conical, about as long as the shell. Feet three to four times as long, cylindrical curved, with irregular simple or forked branches like the antlers of a deer. _Dimensions._--Shell diameter 0.1, horn 0.1 long, feet 0.3 to 0.4 long. _Habitat._--Central Pacific, Station 266, depth 2750 fathoms. Genus 509. _Archipera_,[126] Haeckel, 1881, Prodromus, p. 429. _Definition._--#Archiperida# (vel Monocyrtida triradiata clausa) without internal columella, with two or more apical horns. The genus _Archipera_ differs from the preceding _Peridium_ only in the multiplication of the apical horn, which in the latter is always simple. The number of horns is usually two or three, sometimes four or more. The species bearing three horns may be derived directly from _Triceraspyris_ by loss of the sagittal ring. 1. _Archipera cortiniscus_, n. sp. (Pl. 98, fig. 5).