1310 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus 579. Sethocapsa, 1 Haeckel, 1881, Prodromus, p. 433 (sensu emendate). 



Definition. S ethocapsida (vel Dicyrtida eradiata clausa) with a free cephali 

 bearing an apical horn. 



The genus Sethocapsa and the two following genera represent together the small 

 subfamily of Sethocapsida, or those Dicyrtida in which the mouth of the thorax is 

 closed, and no radial apophyses are present. Sethocapsa may be derived either from 

 Lithopera by loss of the three radial rods, or from Sethocyrtis by closure of the mouth. 



1. Sethocapsa pyriformis, n. sp. (PI. 57, fig. 2). 



Shell rough, pear-shaped, with slight collar stricture. Length of the two joints = 3:10, 

 breadth = 3:8. Cephalis subspherieal, with numerous small pores, and a short pyramidal or 

 conical horn of half the length. Thorax ovate, with subregular, circular, quincuncial pores. 



Dimensions. Cephalis 0'03 diameter, thorax 01 long, 0'08 broad. 



Habitat. Central Pacific, Stations 263 to 274, depth 2350 to 3000 fathoms. 



2. Sethocapsa lagena, Haeckel. 



Lithopera lagena, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. iii. fig. 4. 



Shell smooth, pear-shaped, with sharp colkr stricture. Length of the two joints = 3:8, 

 breadth = 3:6. Cephalis pear-shaped, with few scarce pores, and a small conical horn of half the 

 length. Thorax pear-shaped, with irregular, roundish pores. This species differs from the similar 

 Lithopera lagena almost only in the complete absence of the three internal radial collar beams 

 inside the thorax, and may be derived from it by their retrograde metamorphosis. 



Dimensions. Cephalis 0'03 diameter, thorax 0'08 long, 0'06 broad. 



Habitat. Fossil in Barbados. 



3. Sethocapsa macroceros, n. sp. 



Shell smooth, pear-shaped, with slight collar stricture. Length of the two joints = 2 : 11, 

 breadth = 2 : 9. Cephalis subspherieal, with small circular pores, and a very large, straight, pyra- 

 midal horn, of about the same length as the shell. Thorax ovate, with large, irregular, roundish pores, 

 which are surrounded by polygonal frames. 



Dimensions. Cephalis 0'02 diameter, thorax Oil long, 0'09 broad. 



Habitat. Central Pacific, Station 270, depth 2925 fathoms. 



1 Sethocapsa = Sieve-capsule ; uijfc, x.ii\f,. 



