Shell double, with an external mantle (no horn), 521. _Arachnocalpis_. ------------------------------------------------------------------------- II. Subfamily Archiphænida. Basal mouth closed by a lattice-plate. -------------------- In the axis of the shell-cavity a free columella. ------------------------------------------------------------------------- In the axis of the { Columella simple, 522. _Phænocalpis_. shell-cavity a { free columella. { Columella branched, 523. _Phænoscenium_. ------------------------------------------------------------------------- Shell-cavity simple, without axial columella. ------------------------------------------------------------------------- Shell-cavity simple, { Apex with a horn, 524. _Calpophæna_. without axial { columella. { No apical horn, 525. _Archiphæna_. {1159}Subfamily 1. ARCHIPHORMIDA, Haeckel, 1881, Prodromus, p. 428. _Definition._--#Phænocalpida# with the basal mouth of the shell open (vel Monocyrtida multiradiata aperta). Genus 511. _Bathropyramis_,[128] Haeckel, 1881, Prodromus, p. 428. _Definition._--#Archiphormida# (vel Monocyrtida multiradiata aperta) with simple, slender pyramidal shell and numerous radial beams (six to nine or more). Network simple, with large, unfenestrated, quadrangular meshes. The genus _Bathropyramis_ and the following four nearly allied genera form together a peculiar group of Archiphormida, the Litharachnida, possessing near relations to _Sethopyramis_ and the allied Sethophormida, from which they are probably derived by reduction and loss of the small cephalis. The shell in all these forms is distinctly pyramidal, composed of numerous divergent radial beams (commonly six to nine), which form the edges of the pyramid, and are connected by parallel horizontal rings. The quadrangular meshes so produced are quite simple in _Bathropyramis_. This genus cannot be sharply separated from _Sethopyramis_, its ancestral form. Subgenus 1. _Acropyramis_, Haeckel, 1881, Prodromus, p. 428. _Definition_.--Shell smooth, without spines on the surface. 1. _Bathropyramis acephala_, n. sp. Shell smooth, slenderly pyramidal, with three cortinar pores at the apex and with six stout radial beams or longitudinal ribs, connected by twelve to sixteen complete hexagonal horizontal rings. Meshes nearly square, increasing gradually in size towards the mouth. _Dimensions._--Shell 0.25 long, 0.15 broad. _Habitat._--South Pacific, Station 295, depth 1500 fathoms. 2. _Bathropyramis quadrata_, n. sp. (Pl. 54, fig. 1). Shell smooth, slenderly pyramidal, with three cortinar pores at the apex and nine stout radial beams, connected by eight to twelve complete circular horizontal rings. Meshes subregular, square, increasing in size gradually towards the circular mouth. _Dimensions._--Shell 0.2 to 0.3 long, 0.12 to 0.2 broad.