84. THE OCEAN WORLD. 
the basis of his arrangement. These six families include sixty genera, 
and more than 1,600 species, the families being as follows :— 
I. Monostega,—Body consisting of a single segment. Shell of a 
single chamber. : ; 
Il. Stichostega.—Body composed of segments, arranged in a single 
Fig. 17.— Orbulina 
Fig. 19.—Operculina. Fig. 20._Nummulina perforata. 
universa, 
Fig. 18.—Dentalina 
subarcuata. 
Fig. 21.—Cassidulina Fig. 22.—Textularia Fig. 23.—Spiroloculina 
levigata, variabilis. depressa, 
single line. Shell in chambers, superimposed linearly on a straight 
or curved axis. ’ 
’ II. Helicostega.—Body composed of segments, spirally arranged. 
Chambers piled or superimposed on one axis, forming a spiral. 
IV. Lxtomiostega.—Body composed of alternating segment form- 
ing a spiral. Chambers superimposed on two alternating axes, also 
forming a spiral, 
V. Enallostega.—Body composed of alternate segments not 
