1248 THE VOYAGE OF H.M.S. CHALLENGER. 



Subgenus 6. Astrophormis, Haeckel. 



Definition. Thorax with a variable number of radial ribs (twelve to twenty or 

 more). 



15. Sethophormis aurclia, n. sp. (PJ. 55, figs. 3, 4). 



Leptarachnium aurelia, Haeckel, 1879, Manuscript et Atlas. 



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

 Collar-septum with four large meshes, separated by a cross of four bars, opposite in pairs. Thorax 

 flatly campanulate, with delicate, subregular, hexagonal meshes, and twenty-four prominent radial 

 ribs ; four of these are primary or perradial (centrifugal prolongations of the four bars of the collar- 

 septum); four others are interradial or secondary, alternating with the former at angles of 45; 

 sixteen others are adradial or tertiary, interpolated between the first and second more or less irre- 

 gularly. In some specimens the disposition of the twenty-four ribs was more regular, in others more 

 irregular, than in the specimen figured (figs. 3, 4). The central capsule (fig. 4) exhibits a flat, cap- 

 shaped part with the nucleus (enclosed in the cephalis), and four large, pear-shaped lobes protruded 

 through the four large collar holes (somewhat deformed in the preparation figured). The wall of the 

 thorax exhibits at the base four larger, nearly semicircular pores, bisected by the four primary 

 thoracic ribs. Peristome with twenty-four indentations (between the prominent distal ends of the 

 twenty-four ribs), often more distinct than in ttie specimen figured. 



Dimensions. Cephalis O03 long, O08 broad ; thorax 01 to 0'2 long, 0'4 to 0'6 broad. 



Habitat. Central Pacific, Station 263 to 274, depth 2350 to 2925 fathoms. 



16. Sethophormis dodecaster, n. sp. .(PI. 56, fig. 12). 



Cephalis small, flatly cap-shaped, with irregular, small, roundish pores. Thorax flatly conical, 

 nearly of the same shape as in -the preceding species, but. only with twelve prominent ribs; four 

 primary or perradial ribs (as prolongations of the four crossed cortinar bars), and eight adradial ribs 

 interpolated between the former, and arising at some distance from the collar ring. Peristome with 

 twelve prominent pointed lobes {supported by the distal ends of the twelve ribs), and with twelve 

 semicircular bosoms between them. (The specimen figured is young and not fully developed.) 



Dimensions. Cephalis 0'02 long, 0'04 broad ; thorax 01 long, 0'3 broad. 



Habitat. South Pacific, Station 298, depth 2225 fathoms. 



,17. Sethophormis umbrella, n. sp. (PI. 70, figs. 4, 5). 



Cephalis large, flatly cap-shaped, with irregular, small polygonal meshes. Thorax flat, umbrella- 

 shaped, with subregular, hexagonal meshes, and sixteen strong radial ribs. Four of these are per- 

 radial, and centrifugal prolongations of the four crossed collar beams ; four others are interradial, and 



