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



1. Larnacantha dissacantha, n. sp. 



Cortical shell smooth, with two large cyliudrical spines,. opposite on the poles of the principal 

 axis, and somewhat longer than it. Pores regular, circular, three times as Inroad as the bars ; about 

 eleven on the half meridian. Proportion of the three axes = 2:3:4. Medullary shell one-third as 

 large as the cortical shell. 



Dimensions. — Length of the cortical shell (principal axis) 013, breadth (transverse axis) 0"1, 

 height (sagittal axis) 0-07 ; pores 0-000, bars 0-003 ; length of the LaniaciUa-shaj)ed medullary shell 

 0-045. 



Habitat.- — North Pacific, Station 25G, depth 2950 fathoms. 



2. Larnacantha staiiracantha, n. s]). 



Cortical shell smooth, with four large conical spines in the lateral plane, two larger opposite on 

 the poles of the principal, two smaller on those of the transverse axis. Pores regrdar, circular, 

 twice as broad as the bars ; about seventeen on the half meridian. Proportion of the three axes = 

 3 : 3-5 : 4. Medullary shell one-third as large as the cortical shell. 



Dimensions. — Length of the cortical shell 0-15, breadth O'lS, height O'll ; pores O'OOS, bars 

 0-004 ; length of the medullary shell 0-05. 



Kahitat. — Pacific, central area. Station 2*74, surface. 



3. Larnacantha qiiadricornis, n. sp. 



Cortical shell spiny, -with four strong, horn-Hke curved spines in the lateral plane, opposite in 

 pairs on the poles of the crossed diagonal axes. Pores irregular, roundish, twice to four times as 

 broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2:3:4. 

 Medullary shell one-third as large as the cortical shell. 



Dimensions. — Length of the cortical shell 0-14, breadth 0-11, height 0-07; pores O'OOO to 0-012, 

 bars 0-003 ; length of the meduUary shell 0-05. 



Habitat.- — Pacific, central area. Station 270, surface. 



4. Larnacantha hexacantha, n. sp. (PI. 50, fig. 4). 



Cortical shell thorny, with six strong conical radial spines in the lateral plane, two opposite on 

 the poles of the principal axis, four others opposite in pairs on the poles of the two crossed diagonal 

 axes. Pores with peculiar distribution ; twelve large elliptical pores (nearly of the size of the 

 medullary shell) symmetrically disposed in four crossed meridians (between the sagittal and the 

 lateral meridians), separated by liands of smaller irregular pores. Proportion of the three axes = 

 3:4:5. Medullary shell hexagonal, one-third as large as the cortical shell. 



Dimensions. — Length of the cortical .shell 0-14, breadth 0-11, height O'OS ; large pores 0-04, small 

 pores 0-003 to 0-01, bars 0-004 ; length of the medullary shell O'Oo. 



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



