170 



THE VOYAGE OF H.M.S. CHALLENGER. 



that two pairs or all three j^airs of spines become different ; very rarel)^ 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 ec[ual 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, HexalonchicUum), in which all three pairs 

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

 line system. 



Synoj^sis of the Genera of Cubo»plia.rida. 



I. Subfamily 



Hexastylida. ■! „■ ■ £ i-a- i 



(Shell one simple latticed sphere.) Six spmes of dlflerent 



All six radial spines simple, of equal size, 



s spines of difl'ep 

 sizes, aU six simple. 



Two pairs equal, one pair 

 different, . 



All three pairs different, 



f 



, „ . , . , . e i Spines simple 



All SIX radial spines ot J ^ ^ ' 



II. Subfamily I 



Hexaloncbida. J 



(Shell composed of two concentric ' 

 latticed spheres.) 



equal size. 



Six spines simple, in 

 pairs of different sizes. 



Spines branched, . 



Two pairs equal, one pair 

 different, . 



All three pairs different, 



f ,,, . J. , . ,. { Spines simple, 



All six radial spines oi J '^ '^ ' 



III. Subfamily equal size. 1 o • i i, j 



XT i.- J ^ ( Spines branched, . 



Hexacontida. ■{ v r > 



(Shell composed of three spheres. ) . ■ , ,■ m 



Six spines simple, of Two pairs equal, one pair 



different sizes. different, . 



IV. Subfamily 



Hexacromyida. 



(Four concentric spheres.) 



V. Subfamily 



Ilexacaryida. 

 (Five or more spheres.) 



VI. Subfamily 



Hexadorida. 



I All six radial spines of Spines simple, not 

 j equal size. 



branched, . 



) AH • J- 1 • t { Spines simijle, 



( All SIX radial spines of J '^ ^ 



( equal size. 



1 



All six radial spines of 

 (Shell a spongy sphere, with or \ equal size, simple (not 

 without an enclosed central j branched), 

 medullary shell.) i 



Spines branched, . 



Without latticed medul- 

 lary shell, . 



With one single medul- 

 lary shell. 



With two meduUary 

 shells, 



72. Hexastylus. 



73. Hexastylarium. 



74. Hexastylidium. 



75. Hexalonche. 



76. Hexancistra. 



77. Hexaloncharium. 



78. Hexalonchidium. 



79. Hexacontium. 



80. Hexadendron. 



81. Hexacontarium. 



82. Hexacromyum. 



83. Cubospluera. 



84. Hexaearymn. 



85. Cubaxonium. 



86. Hexadoras. 



87. Hexadoridium. 



