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



Dimensions. — Diameter of the shell 0'21 ; length of the two equatorial sijiiies 0'24, of 

 the eighteen others 0-08 to 01 ; basal breadth of the six larger spines 005, of the fourteen others 

 0-0 1. 



Habitat. — AVesteni Tropical Pacific, Station 224, surface. 



5. Ilexalaspis hexaglypha, b. sj). 



Six hydrotomical spines of unequal size ; the two equatorial very large, six-sided prismatic, twice as 

 long as the diameter of the shell and four times as long as the four pyramidal polar spines ; each of 

 these six spines with six deep furrows between the six prominent edges. The fourteen other 

 spines very thin, compressed, two-edged, about as long as the radius of the shell. 



Dimensions. — Diameter of the shell Oil ; length of the two equatorial spines 0'2, of the eighteen 

 others 0'04 to 0'06 ; baisal breadth of the six larger spines 0'03, of the fourteen others O'Ol. 



Habitat. — Tropical Atlantic, Station 352, surface. 



Geuus 377. Hexaconus,^ n. gen. 



Dejlnition. — Hexalaspida with twenty prominent radial spines, whicli are 

 surrounded at the base by prominent sheaths ; the six hydrotomical spines much larger 

 than the fourteen others. 



The genus Hexaconus differs from the preceding Hexalaspis in the development of 

 conical or cylindrical sheaths surrounding the basal parts of the radial spines ; these 

 sheaths are developed sometimes around all twenty spines, sometimes only around the 

 six larger hydrotomical spines. 



Subgenus 1. Hexaconarium, Haeckel. 

 Definition. — Six hydrotomical spines of equal size. 



1. Hexaconus ciliatu.i, n. sp. (PI. 139, fig. 3). 



All six hydrotomical spines of nearly equal size, pyramidal, with six prominent edges, somewhat 

 longer than the radius of the shell. Sheaths sulcated, finely ciliated at the mouth, twice as broad 

 as long and only one-fourth as long as the spines. The fourteen smaller spines very thin, bristle- 

 shaped, shorter than the radius of the shell. 



Dimensions. — Diameter of the shellO'16; length of the six hydrotomical spines Oil ; Ijasal 

 breadth 0-03. 



Habitat. — Central Pacific, Station 270, surface. 



' Hexaconus = She]l with six cones ; t'la, xiJuof. 



