1288 THE VOYAGE OF H.M.S. CHALLENGER. 



4. Clistophcena armata, n. sp. (PL 57, fig. 7). 



Shell spiny, with deep collar stricture. Length of the two joints = 4 : 18, breadth = 5 : 15. 

 Cephalis subspherical, with small, circular, hexagonally-framed pores, and a stout, three-sided 

 prismatic, cuspidate horn of the same length. Thorax pear-shaped, with regular, circular pores 

 and three pairs of stout pyramidal wings, placed in the three primary meridional planes of the 

 collar beams ; three of them lie in the upper, and three in the lower third of the thorax. Margin 

 of the flat Base with nine cylindrical, somewhat club-shaped, divergent feet. 



Dimensions. Cephalis 0'04 long, O05 broad ; thorax 0'18 long, 0'15 broad. 



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



5. Clistophcena enneolena, n. sp. 



Shell spiny, with sharp collar stricture. Length of the two joints = 4 : 20, breadth 5 : 16 . 

 Cephalis hemispherical, hyaline, with a stout conical horn of the same length and some small 

 accessory horns. Thorax ovate, spiny, with subregular, circular pores. Margin of the vaulted 

 base with nine divergent, conical feet, half as long as the thorax. 



Dimensions. Cephalis 0'04 long, 0'05 broad; thorax 0'2 long, 016 broad. 



Habitat. South Pacific, Station 296, depth 1825 fathoms. 



6. Clistophcena polyolena, n. sp. 



Shell smooth, conical, with obliterated collar stricture. Length of the two joints = 1:5, 

 breadth = 2:5. Cephalis hemispherical, with small, circular pores and two divergent conical 

 horns (a major occipital and a smaller frontal horn). Thorax obtusely conical, with regular, 

 hexagonal pores at the mantle, and circular pores in the basal plate, the margin of which bears 

 eighteen vertical, parallel, conical feet, as long as the cephalis. 



Dimensions. Cephalis 0'015 long, 0'025 broad ; thorax O'OS long, 0'08 broad. 



Habitat. Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms. 



Family LXIV. S ETHOCYRTIDA, n. fam. 



Sethocorida et Sethocapsida, Haeckel, 1881, Prodromus, pp. 439, 433. 



Definition. D icyrtida eradiata. (Cyrtoidea with a two-jointed shell, 

 divided by a transverse constriction into cephalis and thorax, without radial apophyses). 



The family Sethocyrtida, composed of the Sethocorida and Sethocapsida of my 

 Prodromus, comprises those Cyrtoidea in which the shell is two-jointed and bears no 

 radial apophyses. The two subfamilies differ in the shape of the mouth, which in the 

 Sethocorida is a simple wide opening, and in the Sethocapsida is closed by a lattice- plate. 

 The former are here divided into eight, the latter into three genera, 



