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BULLETIN 104, UNITED STATES NATIONAI. MUSEUM. 



Distribution. — Specimens of this species occur very widely dis- 

 tributed, as would be expected of a species which is so well adapted 

 for a pelagic life. It is very finely developed and very abundant 

 in the bottom samples from the Caribbean, but good specimens are 

 found in most bottom samples where Globigerinidae occur at all. 

 The specimens outside the Tropics, however, are usually smaller. 



The adaptation to the pelagic condition is first of all brought 

 about by the spherical form. There are a great many small open- 

 ings beside the ordinary punctae and one opening of still larger 

 size, thus allowing easy access for the protoplasm to the exterior. 

 In a living pelagic specimen there are developed very numerous 

 elongate spines from the exterior and these evidently serve in some 

 way to support the extended protoplasm. 



The young is Globigerine in character and shows that Orhulina 

 belongs to that group and is a genus derived from a Globigerine 

 ancestry. The addition of the spherical chamber comes as the last 

 character in its development. There are many spherical chambers 

 in which these early chambers do not appear. This may be from 

 two causes. One may be that the earlier chambers are resorbed as 

 occurs elsewhere in the animal kingdom. The other is that these 

 may be microspheric forms of the species and the earlier develop- 

 ment retained as is the case elsewhere among the foraminifera, the 

 smaller globular chambers without the early stages being the mega- 

 lospheric form of the specie.?. Whether the globular chamber grows 

 larger at all after its development is a mooted question. There 

 are often found specimens, especially among the larger ones, in 

 which several layers of the test are developed. These may possi- 

 bly be additions on the exterior of the smaller test represented by 

 the inner layer. 



In some specimens two large chambers are developed instead of 

 one, a condition that would be easily accounted for on the basis 

 of development of a final globular chamber after a series of coiled ones. 



Orbulina univerm — material examined. 



