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



The two hydrotomical spines very thick and short, pyramidal, little prominent. Short rudiments of 

 the eighteen other spines present, bristle-shaped. 



Dimensions. Length of the shell 01, breadth 0'05. 



Habitat. South Atlantic, Station 335, surface. 



Subgenus 2. Diplocolpium, Haeckel. 



Definition. Mantle of the double cone compressed from both poles of the 

 shortened geotomical axis ; its transverse section therefore elliptical. 



3. Diplocolpus serratus, n. sp. (PL 140, fig. 5). 



Mantle of the double cone thick walled, compressed, with elliptical transverse section ; its 

 surface with numerous delicate ribs ; contour little convex ; margin regularly serrate. Hydrotomical 

 spines short, pyramidal, with six serrate wings. Transverse diameter of the shell nearly twice as 

 great at the polar mouth as at the equator and half as long as the whole shell. 



Dimensions. Length of the shell 015 ; breadth on the equator 0'035, on the poles 0'07. 



Habitat. Central Pacific, Station 274, surface. 



4. Diplocplpus dentatus, n. sp. (PL 140, fig. 9). 



Mantle of the double cone thin walled, compressed, with elliptical transverse section ; its contour 

 straight ; siirface with six deeper and numerous shallower furrows ; margin denticulated, with six 

 triangular prominent larger teeth. Hydrotomical spines very large prismatic, pyramidal at 

 the ends. Transverse diameter of the shell -a little larger at the polar mouth than at the equator 

 and half as long as the whole shell. 



Dimensions. Length of the shell 0'2 ; breadth on the equator 0'08, on the poles 01. 



Habitat. North Pacific, Station 244, surface. 



5. Diplocolpus sulcatus, n. sp. (PL 140, fig. 8). 



Mantle of the double cone thin walled, compressed, with elliptical transverse section ; its contour 

 straight ; surface with twelve to sixteen deep longitudinal furrows, which are separated by thin, 

 undulating, double edged ribs ; margin little dentated. Hydrotomical spines short, pyramidal, with 

 six dentate wings. Transverse diameter of the shell a little larger at the polar mouth than at the 

 equator, about one-third of the whole length of the shell. 



Dimensions. Length of the shell 017 ; breadth on the equator 0'05, on the poles 0'06. 



Habitat. -South Pacific, Station 291, surface. 



