8 4 



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. 



II. Stichostega. Body composed of segments, arranged in a single 



Operculina. Fig. 20. Nummulina perforat 



Fig. 21. Cassidulina 

 laevigata. 



Fig. 22. Textularia 



variabilis. 



Fig. 23. Spiroloculina 

 depressa. 



single line. Shell in chambers, superimposed linearly on a straight 

 or curved axis. 



III. Helicostega. Body composed of segments, spirally arranged. 

 Chambers piled or superimposed on one axis, forming a spiral. 



IV. Entomiostega. Body composed of alternating segment form- 

 ing a spiral. Chambers superimposed on two alternating axes, also 

 forming a spiral. 



"V. Enallostega. Body composed ot alternate segments not 



