Shell ovate, smooth, very thick-walled, one and a third times as long as broad. Pores very numerous and small, subregular circular, forty to fifty on the greatest breadth of the shell, of about the same breadth as the bars. Peristome small, constricted, scarcely one-fourth as broad as the shell, with twelve to fifteen short triangular vertical feet. _Dimensions._--Shell 0.28 to 0.31 long, 0.21 to 0.23 broad; mouth 0.06 to 0.07 broad. _Habitat._--Fossil in Barbados. 4. _Carpocanistrum acephalum_, n. sp. (Pl. 52, fig. 10). Shell ovate, smooth, thin-walled, one and a fifth times as long as broad. Pores subregular circular, twice as broad as the bars, sixteen to twenty on the greatest breadth of the shell. Peristome slightly constricted, with fifteen to eighteen slender, slightly bent, nearly vertical, and parallel feet, which are half as long as the shell. _Dimensions._--Shell 0.12 long, 0.1 broad; mouth 0.07 broad. _Habitat._--North Pacific, Station 241, depth 2300 fathoms. {1172}5. _Carpocanistrum evacuatum_, n. sp. (Pl. 52, fig. 11). Shell urceolate, smooth, thin-walled, one and a half times as long as broad. Pores regular circular, sixteen to twenty on the greatest breadth of the shell. Peristome slightly constricted, with twenty to twenty-five small triangular vertical feet. _Dimensions._--Shell 0.1 long, 0.07 broad; mouth 0.05 broad. _Habitat._--Central Pacific, Station 272, depth 2600 fathoms. 6. _Carpocanistrum pyriforme_, Haeckel. _Lithocarpium pyriforme_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 97, Taf. iii. fig. 10. Shell pear-shaped or subspherical, one and a fourth times as long as broad. Pores roundish, polygonally framed (or with square meshes ?). Peristome strongly constricted, one-fourth as broad as the shell, somewhat tubular, with twelve to twenty short vertical and parallel feet. The position of this species is doubtful; perhaps it represents a peculiar genus. _Dimensions._--Shell 0.17 long, 0.14 broad; mouth 0.035 broad. _Habitat._--Fossil in Tertiary rocks of Sicily (Grotte) Stöhr. Genus 521. _Arachnocalpis_,[138] Haeckel, 1881, Prodromus, p. 427. _Definition._--#Archiphormida# (vel Monocyrtida multiradiata aperta) with an ellipsoidal or nearly spherical double shell; outer shell arachnoidal or spongy. Peristome small, constricted with a corona of numerous radial feet. No apical horn. The genus _Arachnocalpis_ differs from the other Archiphormida by possessing a double shell (like _Peripyramis_). The large shell, reaching nearly half a millimeter in length is either ellipsoidal or nearly spherical, and composed of an inner primary and an outer secondary shell. Its network is very delicate, in the outer envelope either spongy or arachnoidal. This very remarkable genus has probably no true relation to the other Archiphormida but has been derived from true #Calpoidea# (_Mitrocalpis_) by development of a corona around the mouth. 1. _Arachnocalpis ellipsoides_, n. sp. (Pl. 98, fig. 13).