Page:Scientific results HMS Challenger vol 18 part 1.djvu/378

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 Cubosphærida, 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 crystalline system.

Synopsis of the Genera of Cubosphærida.

I. Subfamily Hexastylida. (Shell one simple latticed sphere.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	All six radial spines simple, of equal size,			72. Hexastylus.
		Six spines of different sizes, all six simple.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two pairs equal, one pair different,	73. Hexastylarium.
				All three pairs different,	74. Hexastylidium.
II. Subfamily Hexalonchida. (Shell composed of two concentric latticed spheres.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	All six radial spines of equal size.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Spines simple,	75. Hexalonche.
				Spines branched,	76. Hexancistra.
		Six spines simple, in pairs of different sizes.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}$	Two pairs equal, one pair different,	77. Hexaloncharium.
				All three pairs different,	78. Hexalonchidium.
III. Subfamily Hexacontida. (Shell composed of three spheres.)	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \ \end{matrix}}\right.}$	All six radial spines of equal size.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Spines simple,	79. Hexacontium.
				Spines branched,	80. Hexadendron.
		Six spines simple, of different sizes.		Two pairs equal, one pair different,	81. Hexacontarium.
IV. Subfamily Hexacromyida. (Four concentric spheres.)	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$	All six radial spines of equal size.		Spines simple, no branched,	82. Hexacromyum.
V. Subfamily Hexacaryida. (Five or more spheres.)	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	All six radial spines of equal size.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Spines simple,	83. Cubosphæra.
				Spines branched,	84. Hexacaryum.
VI. Subfamily Hexadorida. (Shell a spongy sphere, with or without an enclosed central medullary shell.)	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,}$	All six radial spines of equal size, simple (not branched).	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right.}$	Without latticed medullary shell,	85. Cubaxonium.
				With one single medullary shell,	86. Hexadoras.
				With two medullary shells,	87. Hexadoridium.