1256 THE VOYAGE OF H.M.S. CHALLENGER. 



Subgenus 3. Actinopyramis, Haeckel. 



Definition. Pyramidal shell with twelve or more radial beams (commonly twelve to 

 twenty-four, sometimes forty or more). 



10. Sethopyramis dodecalactis, n. sp. 



Shell smooth, slender, pyramidal. Cephalis small, spherical, hyaline, with a short conical horn. 

 Thorax with twelve radial ribs in the upper half, between which twelve others are interpolated in 

 the lower half. These are connected by twenty to twenty-four complete transverse rings. The 

 meshes so produced are subregular, rectangular. 



Dimensions. Cephalis 0'03 diameter ; thorax 0'6 long, 0'2 broad. 



Habitat. Indian Ocean, Madagascar (Eabbe), surface. 



11. Sethopyramis bicornis, n. sp. 



Shell spiny, slender, pyramidal. Cephalis small, spherical, hyaline, with two divergent conical 

 horns, the major (occipital) three times and the minor (frontal) twice as long. Thorax slender, 

 pyramidal, campanulate, thorny, with twenty to thirty radial beams, which are little curved, convex 

 in the upper, concave in the lower half, and connected by numerous interrupted transverse bars. 

 Meshes in the upper third rounded, in the lower two-thirds quadrangular, of very different sizes. 

 Surface covered with spinules. 



Dimensions. Gephalis O02 diameter ; thorax O9 long, - 4 broad. 



Habitat. North Pacific, Station 241, depth 2300 fathoms. 



12. Sethopyramis maxima, n. sp. 



Shell smooth, slender, pyramidal. Cephalis small, spherical, with few small pores, and a stout, 

 vertical, conical horn twice the length. Thorax very prolonged, conical, with straight lateral out- 

 lines and numerous (twenty to fifty) radial beams (in the upper third twelve, in the middle third 

 twenty-four, in the lower third forty to fifty, by interpolation); they are connected by very numerous 

 interrupted transverse bars. Meshes subregular, quadrangular. Surface smooth. 



Dimensions. Cephalis 0'02 diameter ; thorax T05 long, 0'45 broad. 



Habitat. Central Pacific, Station 271, depth 2425 fathoms. 



Genus 561. Plectopyramis, 1 Haeckel, 1881, Prodromus, p. 432. 



Definition, S ethophormida (vel Dicyrtida multiradiata aperta) with numerous 

 straight or slightly curved radial ribs in the wall of the pyramidal thorax. Network 

 double, the large primary meshes being fenestrated by fine secondary network. Cephalis 

 commonly without horn. 



1 Plectopyramis = Woven pyramid ; ^AEXTO'S, wt/ja^iV. 



