Shell slender, pyramidal, with nine strong radial beams, connected by fifteen to twenty transverse horizontal rings, which are partly complete, partly interrupted. Meshes subregular, square. From the nodal points of the surface there arise branched spines, which at equal distances from it are connected by thin threads, forming a delicate outer arachnoidal shell with large irregular polygonal meshes. _Dimensions._--Shell 0.32 long, 0.16 broad. _Habitat._--Central Pacific, Station 271, depth 2425 fathoms. 2. _Peripyramis spongiosa_, n. sp. Shell slender, pyramidal, with nine strong radial beams, connected by twelve to eighteen irregular interrupted rings. Meshes irregular, square or polygonal. From the whole surface arise numerous branched spines, which by communication and dense ramification form an outer spongy envelope around the shell. (Similar to _Spongopyramis spongiosa_, Pl. 56, fig. 10.) _Dimensions._--Shell 0.45 long, 0.32 broad. _Habitat._--Central Pacific, Station 274, depth 2750 fathoms. {1163}Genus 514. _Litharachnium_,[131] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 835. _Definition._--#Archiphormida# (vel Monocyrtida multiradiata aperta) with flatly conical, tent-shaped or nearly discoidal shell, and numerous, simple, radial beams in its wall. The genus _Litharachnium_, and the closely allied genus _Cladarachnium_, differ from the preceding similar genera mainly in the flat form of the depressed shell, which is not slenderly pyramidal, but more tent-shaped or nearly discoidal. The radial ribs are generally not straight, but more or less curved. The top of the tent exhibits three or four important meshes, the original pores of the cortinar septum. _Litharachnium_ may be derived directly from _Sethophormis_ by reduction and loss of the cephalis. Subgenus 1. _Litharachnidium_, Haeckel. _Definition._--Apex with three cortinar pores (one odd sternal and two paired cardinal pores). 1. _Litharachnium tentorium_, Haeckel. Litharachnium tentorium, Haeckel, 1862, Monogr. d. Radiol., p. 281, Taf. iv. figs. 7-10. Shell flatly conical or tent-shaped, with concave lateral outlines. Apex with three equal cortinar pores. Twenty radial ribs at nearly equal distances. Between them very numerous and thin secondary ribs, crossed by more than one hundred concentric rings. Pores square, as in all the following species. Margin truncate, circular. _Dimensions._--Shell 0.35 long, 0.8 broad. _Habitat._--Mediterranean (Messina). 2. _Litharachnium araneosum_ (Pl. 55, figs. 8, 10). Shell flatly conical, nearly discoidal, with straight lateral outlines. Apex with three unequal cortinar pores (one odd smaller sternal and two paired larger cardinal pores). Twenty radial ribs at unequal distances, with numerous intercalated secondary ribs. Margin ciliate. _Dimensions._--Shell 0.18 long, 0.32 broad. _Habitat._--Central Pacific, Station 271, surface. {1164}3. _Litharachnium arachnodiscus_, Haeckel.