170 



THE VOYAGE OF H.M.S. CHALLENGER. 



that two pairs or all three pairs of spines become different ; very rarely, also both spines 

 of one pair become unequal (probably only an individual abnormality). Those variations 

 correspond to the differences between the crystalline systems. The common Cubo- 

 sphserida, with three equal spine-pairs, correspond to the regular or cubic system, with 

 three equal axes. The rarer forms (Hexastylarium, Hexaloncharium, Hexacontarium) 

 exhibit two equal pairs and one different pair ; they correspond to the quadratic 

 system, with three perpendicular axes, two of which are equal, the third unequal. Still 

 more rare are those forms (Hexastylidium, Hexalonchidium), in which all three pairs 

 of spines are different, corresponding to the three unequal axes of the rhombic crystal- 

 line system. 



Synopsis of the Genera of Cubosphcerida. 



I. Subfamily 



Hexastylida. 

 (Shell one simple latticed sphere. ) 



II. Subfamily 



Hexalonchida. 



(Shell composed of two concentric 

 latticed spheres.) 



III. Subfamily 



Hexacontida. 

 (Shell composed of three spheres. ) 



IV. Subfamily 



Hexacromyida. 

 (Four concentric spheres.) 



V. Subfamily 



Hexacaryida. 

 (Five or more spheres.) 



VI. Subfamily 



Hexadorida. 

 (Shell a spongy sphere, with or 



without an enclosed central 



medullary shell. ) 



All six radial spines simple, of equal size, 



{Two pairs equal, one pair 

 different, . 

 All three pairs different, 



.., . ,. , . ,i Spines simple, 

 All six radial spines of J 



equal size. 



Spines branched, . 



f Two pairs equal, one pair 

 Six spiues simple, in I different, . 

 pairs of different sizes, j 



[ All three pairs different, 



All six radial spines of 

 equal size. 



Spines simple, 

 Spines branched, . 



Six spines simple, of Two pairs equal, one pair 



different sizes. different, . 



All six radial spines of Spines simple, not 



equal size. branched, . 



I . ,. , . , C Spines simple 



( All six radial spines of I 



- equal size. 



1 



All six radial spines of 

 equal size, simple (not 

 branched). 



Spines 



Without latticed medul- 

 lary shell, . 



With one single medul- 

 lary shell, 



With two medullary 

 shells, 



72. Hexastylus. 



73. Hexastylarium. 



74. Hexastylidium. 



75. Hexalonche. 



76. Hexancistra. 



77. Hexulunchariam. 



78. Hexalonchidium. 



79. Hexacontium. 



80. Hexadendron. 



81. Hexacontarium. 



82. Hexacromyum. 



83. Cubosphcera. 



84. Ilexacaryum. 



85. Cubaxonium. 



86. Ilexadoras. 



87. Hexadoridium. 



