1250 THE VOYAGE OF H.M.S. CHALLENGER. 



The genus Sethamphora differs from the preceding Sethophormis, and from the next 

 following ribbed Sethophormida, mainly in the small, more or less constricted mouth ; 

 therefore the thorax is more or less ovate, and its ribs curved, with the convexity external. 

 Sethophormis may be divided into two different subgenera, Dictyoprora and Cnjpto- 

 cephalus; in the former the cephalis is perfectly free and well developed, in the latter 

 it is more or less hidden in the uppermost part of the thorax (like Carpocanium). 



Subgenus 1. Dictyoprora, Haeckel, 1881, Prodromus, p. 430. 

 Definition. Cephalis large, perfectly free, not hidden in the thorax. 



1. Sethamphora hexapleura, n. sp. 



Shell ovate, smooth, with distinct collar stricture. Length of the two joints = 3: 11, bread th = 

 5:10. Cephalis large, free, hemispherical, with small circular pores. Thorax truncate, ovate, with 

 six strong curved ribs, and six large triangular meshes between them in the upper half ; five smaller 

 pores between every two ribs in the lower half (in three tiers); therefore, together, thirty-six 

 thoracic meshes. Mouth strongly constricted, smooth, only one-third as broad as the thorax. 



Dimensions. Cephalis 0'03 long, 0'05 broad ; thorax, Oil long, 01 broad. 



Habitat. Central Pacific, Station 266, depth 2750 fathoms. 



2. Sethamphora enneapleura, n. sp. 



Shell subovate, smooth, with 1 slight collar stricture. Length of the two joints = 3 : 9, breadth = 

 4 : 8. Cephalis large, hemispherical, free, with small circular pores. Thorax inflated, ovate, with 

 nine strong curved ribs, which are connected by five transverse circular rings at equal distances. 

 Forty-five rounded, squarish, large meshes between them, in five transverse and nine longitudinal 

 rows. Mouth constricted, smooth, half as broad as the thorax. 



Dimensions. Cephalis 0'03 long, 0'04 broad ; thorax 0'09 long, 0'08 broad. 



Habitat. South Atlantic, Station 332, depth 2200 fathoms. 



3. Sethamphora dodecapleura, n. sp. 



Shell urceolate, smooth, with sharp collar stricture. Length of the two joints = 3:9, breadth 

 = 5:9. Cephalis flat, cap-shaped, free, with twelve ribs, and very small pores between them. 

 Thorax thick -walled, inflated, with subcylindrical cavity, and twelve prominent sharp ribs, alternating 

 with twelve longitudinal rows of very small circular pores (eight pores in each row). Mouth con- 

 stricted, half as broad as the thorax. 



Dimensions. Cephalis 0'03 long, 0'05 broad ; thorax 0'09 long, 0'09 broad. 



Habitat. Western Tropical Pacific, Station 225, depth 4475 fathoms. 



