FORAMINIFERA OF THE ATLANTIC OCEXN. 



39 



Description. — Test inflated, usually somewhat longer than broad, 

 composed of a few chamliers, the earlier ones irregularly spiral, but 

 in the adult three chambers usually making up the entire visible 

 portion of the test ; the fully deyeloped test is marked by fissure-like 

 sutures, the edges of which are slightly carinate, or sometimes becom- 

 ing fimbriate and nearly closing the fissure; Avail thick, in the young 

 translucent but with large perforations, in the adult usually opaque 

 and the perforations very large and conspicuous, sometimes even 

 making the test reticulate and rough ; aperture an arched opening into 

 the chamber from the deep fissure near its base. 



Diameter up to 1 mm. but in adults sometimes exceeding this. 



Distribution.— The Albatross records for the western Atlantic show 

 this species well scattered over the area from off Brazil just south of 

 the Equator to latitude 40° north. It is known as a pelagic species 

 and its distribution tiius roughly corresponds in the Albatross samples 

 wath the general condition of ocean-current movement^n the North 

 Atlantic. 



The best developed specimens are from the Caribbean. Those 

 from other regions are usually less well developed and represent 

 young individuals in many cases. 



The young is generally in the form of a trochoid spire, but the 

 irregular shape is soon taken on. The smooth surface and very 

 coarse punctae will distinguish the young from any of the species of 

 Globigerina. In the young the sutures are not depressed, but as 

 growth progresses the sutures become much depressed and finally 

 in well-developed or senescent specimens the sutural areas become 

 much cleft and the ed^jes of these become fimbriate. 



Sphaeroidina dehiscens — material examined. 



