Shell broad, ovate, rough, spongy, thick-walled; length to the breadth = 4 : 3. Spongy framework very dense and dark, with very small roundish pores. Mouth constricted, with a short tubular peristome, about one-third as broad as the shell. _Dimensions._--Shell 0.35 long, 0.26 broad; mouth 0.08 broad. _Habitat._--Fossil in the Alpine Lias (Schafberg bei Salzburg, Dunikowski). 2. _Spongocyrtis arachnoides_, n. sp. Shell ellipsoidal, spiny, spongy, thin-walled; length to the breadth = 3 : 2. Spongy framework loose and delicate, with irregular polygonal meshes and arachnoidal thread-like bars. Mouth constricted, without peristome, about one-fifth as broad as the shell. (Very similar to _Arachnocalpis ellipsoides_, Pl. 98, fig. 13, but without corona around the mouth.) _Dimensions._--Shell 0.32 long, 0.21 broad; mouth 0.04 broad. _Habitat._--Central Pacific, Station 270, depth 2925 fathoms. Subfamily 2. ARCHICAPSIDA, Haeckel, 1881, Prodromus, p. 428. _Definition._--#Cyrtocalpida#, with the basal mouth of the shell fenestrated (vel Monocyrtida eradiata clausa). Genus 532. _Halicapsa_,[149] Haeckel, 1881 Prodromus, p. 429. _Definition._--#Archicapsida# with an apical horn. The genus _Halicapsa_, and the following closely allied _Archicapsa_, represent together the small subfamily of Archicapsida, or of those Cyrtocalpida, in which the basal mouth of the simple shell is closed by a lattice plate. This may be the original state of this family, if it is derived from the Circospyrida (_Circospyris_, _Dictyospyris_) by loss of the sagittal constriction and the primary ring. But it is also possible that the Archicapsida have been partly derived from the Archicorida by secondary fenestration of the open mouth. The genus _Halicapsa_ may be easily confounded with the similar Ellipsid _Lithapium_ (compare p. 303, Pl. 14, figs. 8-10). The skeleton of both genera may be perfectly similar, the only distinction being the structure of the central capsule, which in _Halicapsa_ is that of the MONOPYLEA, in _Lithapium_ that of the PERIPYLEA. {1190}Subgenus 1. _Calpocapsa_, Haeckel. _Definition._--Surface of the shell smooth or rough, but not spiny. 1. _Halicapsa lithapium_, n. sp. (Pl. 97, fig. 6). Shell pear-shaped, rough, one and a half times as long as broad. Pores subregular, circular, twice as broad as the bars. Basal plate with four larger ovate cortinar pores (two larger cardinal and two smaller jugular), and with six smaller peripheral pores (fig. 6). Horn of the apex three-sided pyramidal, stout, half as long as the shell. _Dimensions._--Shell 0.16 long, 0.1 broad; horn 0.08 long. _Habitat._--North Pacific, Station 244, depth 2900 fathoms. 2. _Halicapsa triglochin_, n. sp. (Pl. 53, figs. 3, 4).