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



equator. Proportion of the three axes = 2:3:4. Medullary shell lentelliptical, of the same form 

 and structure as the cortical, but only one-third as large, connected with it by six thin radial beams, 

 lying in pairs in the three dimensive axes; on the outside they are prolonged into six strong conical 

 radial spines, which are in pairs of different size (as in Larcarium axostylum) ; the length of each 

 spine nearly equals the axis of the cortical shell, of which it is the prolongation. 



Dimensions. Length of the cortical shell (and the principal spines) 0'18, breadth of it (and 

 length of the lateral spines) 0135, thickness of it (and length of the sagittal spines) O09 ; pores 

 0-005 to 0-013, bars 0'003. 



Habitat. Pacific, central area, Station 271, surface. 



4. Larcidium octacanthum, n. sp. 



Cortical shell thorny, with irregular network ; pores roundish, once to four times as broad as 

 the bars ; about thirteen to fifteen on the half meridian, eleven to thirteen on the half equator. 

 Proportion of the three axes = l : 2'5 :4. Medullary shell lentelliptical, one-fifth as large as the 

 cortical, connected with it by eight radial beams, which are situated in two crossed diagonal planes 

 (opposite in pairs), and are prolonged on the surface into eight long and thin cylindrical radial spines 

 similar to Tetrapyle octacantha). 



Dimensions. Length of the cortical shell 016, breadth Oil, thickness 0'045 ; pores 0'003 to 

 0-012, bars 0'003 ; medullary shell 0'02 to 0'03. 



Habitat. Pacific, central area, Station 263, depth 2650 fathoms. 



5. Larcidium. dodecanthum, n. sp. (PI. 50, figs. 8, 8a). 



Cortical shell rough, with irregular network ; pores roundish, twice to four times as broad 

 as the bars ; about twelve to fourteen on the half meridian, eight to ten on the half equator. 

 Proportion of the three axes = 2:3:4. Medullary shell lentelliptical, one-third as large as the 

 cortical, connected with .it by twelve thin radial beams, which are prolonged outside into twelve 

 strong conical radial spines, about half as long as the breadth of the shell. 



Dimensions. Length of the cortical shell 014, breadth 01, thickness 0'07 ; pores O'OOS to 

 0-015, bars 0'004 ; medullary shell 0'04 to 0'05. 



Habitat. South Pacific, Station 288, surface. 



6. Larcidium polyacanthum, n. sp. 



Cortical shell spiny, with irregular network ; pores roundish, once to twice as broad as the 

 bars ; about ten to twelve on the half meridian, six to eight on the half equator. Proportion of 

 the three axes = 1:2:3. Medullary shell lentelliptical, half as large as the cortical shell, connected 

 with it by numerous (twenty to twenty-five) radial beams, which are prolonged outside into three- 

 sided pyramidal spines, about as long as the breadth of the shell. 



Dimensions. Length of the cortical shell 018, breadth 01 2, thickness 0'06 ; pores O'Ol to 

 0-015, bars O'OOS; medullary shell 0'3 to 0'09. 



Habited. North Pacific, Station 244, depth 2900 fathoms. 



