REPORT ON THE RADIOLARIA. 1243 



Subfamily 1. SETHOPHORMIDA, Haeckel, 1881, Prodromus, p. 432. 



Definition. A nthocyrtida with the basal mouth of the shell open (vel Dicyrtida 

 multiradiata aperta). 



Genus 558. Sethophormis, Haeckel, 1 1881, Prodromus, p. 432. 



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

 radial ribs in the wall of the flat and broad, campanulate or nearly discoidal thorax. 

 Cephalis also flat and broad, cap-shaped, without horn. 



The genus Sethophormis comprises a great number of widely distributed and large 

 Dicyrtida, all agreeing in the flat cap-shaped or nearly discoidal form of the thorax, which 

 has constantly a very delicate network, and is pierced by numerous radial beams. Four 

 of these are commonly primary and direct prolongations of the four cortinar rods in the 

 collar septum, whilst the others are secondary or interpolated ribs. Sethophormis may be 

 derived either from the triradial Lamprodiscus by multiplication of the ribs (or interpo- 

 lation of secondary ribs between the three primary), or from Halicalyptra by develop- 

 ment of transverse rods connecting its terminal feet, and forming a ribbed thorax. 

 Corresponding to the number of the ribs, we may distinguish as subgenera (separate 

 genera in my Prodromus, 1881, p. 432) Tetraphormis with four, Pen taphormis with five, 

 Hexaphormis with six, Octophormis with eight, Enneaphormis with nine, and Astro- 

 phormis with ten to twenty or more ribs. The cephalis bears no horn, and is usually 

 large, flat, cap-shaped or hemispherical. 



Subgenus 1. Tetraphormis, Haeckel, 1881, Prodromus, p. 432. 



Definition. Thorax with four radial ribs, opposite in pairs in two meridional planes, 

 perpendicular to one another. Collar septum with four large pores. 



1. Sethophormis cruciata, n. sp. 



Cephalis very large, hemispherical, with irregular, delicate network of small square meshes. 

 Thorax flatly campanulate, with delicate, regular network of small hexagonal meshes. All bars 

 very thin, thread-like. Four stout radial thoracic ribs, crossed in pairs, lie in two meridional planes, 

 perpendicular to one another. Very similar to Sethophormis aurelia (PI. 55, figs. 3, 4), but not so 

 flat, and with only four thoracic ribs. Peristome or margin of the thoracic mouth smooth, circular. 



Dimensions. Cephalis 0'04 long, 0'08 broad ; thorax 0'12 long, - 36 broad. 



Habitat. Central Pacific, Station 271, surface. 



1 Sethophormis = Sieve-basket ; atiS 



