Genus 559. Sethamphora,[[176]] n. gen.
Definition.—Sethophormida (vel Dicyrtida multiradiata aperta) with numerous curved ribs in the wall of the ovate thorax, the small mouth of which is constricted. Cephalis without horn.
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 Cryptocephalus; 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. Dictyoprona, 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, breadth = 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, 0.11 long, 0.1 broad.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
2. Sethamphora enneapleura, n. sp.