GEOGRAPHIC DISTRIBUTION 41 



Globotruncana linneiana (d'Orbigny). 

 Glohotruncana marginata (Reuss). 



To these may be added Tretomphalus bulloides (d'Orbigny) 

 and Hastigerinella digitata (Rhumbler) both so far as known 

 not of oceanic types. 



The two families of the Globigerinidae and Globorotaliidae 

 have developed either very large or multiple apertures, a gen- 

 erally globular or tumid form and a rugose or spinose surface 

 often the surface clothed with long slender spines. Of these, 

 Orbulina has the most perfect adaptation with its entirely spher- 

 ical chamber. 



