1434 THE VOYAGE OF H.M.S. CHALLENGER. 



constricted opening between thorax and abdomen. It may therefore be regarded as a 

 Sethocapsa, which has develoi^ed a third, open, abdominal joint. The cephalis bears 

 an apical horn. 



1. Phrenocodon clathrostomium, n. sp. (PI. 70, figs. 7, 8). 



Shell campanulate-conical, with two deep strictures. Length of the three joints = 2:6:3, 

 breadth = 3 : 10 : 14. Cephalis hemispherical, with an oblique curved horn of the same length. 

 Thorax subconical, with polygonal, roundish pores, increasing in size towards the girdle. A perfect 

 fenestrated diaphragm, with irregular, roundish pores of very different sizes, separates the thorax 

 from the abdomen. Tlie latter is composed of three parallel, circular rings, which are connected 

 by fifteen to twenty radial beams. As the middle ring is larger than the two others, the beams 

 between the large quadrangular pores are divergent in the upper, convergent in the lower girdle. 

 Short prolongations of the divergent beams form a coronal around the middle ring (compare fig. 7 

 profile, fig. 8 from below). 



Dimensions. — Length of the three joints, a 0'02, b 0'06, c 0-03 ; breadth, a 0'03, & 01, c 014. 



Habitat. — Central Pacific, Station 272, depth 2600 fathoms. 



2. Phrenocodon diaphragma, n. sp. 



Shell campanulate-conical, very sunUar to that of the preceding species, but with abdomen and pro- 

 portions different. Length of the three joints = 1:3:2, breadth = 1:4:4. Abdomen cylindrical, 

 with two or three transverse rows of large quadrangular meshes (fifteen to twenty in each row), 

 without the characteristic inflexion of the preceding species, and without the coronal. 



Bimensioyis. — Length of the three joints, a 0-02, h 0-06, c 0-034 ; breadth, a 0-02, b O'OS, c 0-08. 



Habitat. — Central Pacific, Station 271, depth 2425 fathoms. 



Section IV. STICHOCYETIDA, Haeckel, 1862, Monogr. d. Radiol., 

 p. 280, 312 (Pis. 75-80). 



Stichoeyriida et Tetraeyrtida, Haeckel, 1881, Prodromus, p. 437, 438. 



Definition. — C yrtoidea polythalamia, with annulated shell, divided by three to 

 six or more transverse, horizontal constrictions, into four to seven or more annular 

 joints. (The first joint represents the cephalis, the second the thorax, the third the 

 abdomen, all the following joints together a post-abdomen.) 



