1162 THE VOYAGE OF H.M.S. CHALLENGER. 



3. Cinclopyramis lithosestrum, n. sp. 



Shell slender, pyramidal, with twelve strong radial ribs (six primary longer and six secondary 

 shorter) connected by twelve to fifteen interrupted irregular rings. Meshes irregular square or 

 trapezoidal, filled up by a delicate secondary network with irregular polygonal porules. 



Dimensions. — Shell 0-4 to 0-5 long, 0:2 to O'S- broad. 



Habitat. — Fossil in Barbados. 



Geuus 513. Peripyramis,^ Haeckel, 1881, Prodromus, p. 428. 



Definition. — Ar ch iph or mi d a (vel Monocyrtida multiradiata aperta) with 

 double, slenderly pyramidal shell, and numerous radial beams (six to nine or more). 

 Network double, with an external arachnoidal or sj)ongy envelope around the primary 

 lattice-shell. 



The genus Peripyramis diSers from its probable ancestral form, Bathropyramis, by 

 development of a delicate external envelope around the primary shell, and therefore 

 bears to it the same relation that Spongopyramis among the Dicyrtida does to 

 Sethopyramis. It may also be derived directly from the former by loss of the cephalis. 



1. Peripyramis circumtexta, n. sp. (PI. 54, fig. 5). 



Shell slender, pyramidal, with nine strong radial beams, connected by fifteen to twenty trans- 

 verse 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 inteiTupted 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. 



1 Peripj/ramis^ Pyramid with an envelope; wtj;', xyj«^/j. 



