84 



THE OCEAN WORLD. 



the basis of his arrangement. These six famiUes include sixty genera, 

 and more than i,6oo species, the famihes 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 



Fig. 17. — Orbulina 

 universa. 





il^! 





Fig. 19. — Operculina. Fig. 20. — Nummulina perforata. 



Fig. 18. — Dentalina 

 subarcuata. 



Fig. 21. — Cassidulina 

 Ijevigata. 



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. Entomiostcga. — Body composed of alternating segment form- 

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

 forming a spiral. 



V. Enallosiega. — Body composed of alternate segments not 



