Spheraster (an aster in which the centrum is large, with a diameter equal to or greater than one-third the length of the actines), [233]
Sphere, [184]
Spicatae, [362]
Spicules, calcareous, of Coccolithophoridae, [114];
siliceous, of Heliozoa, [71], [74];
of Radiolaria, [83];
of Silicoflagellata, [110];
of Sponges, [170] f.;
composition, [170];