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.
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).