CHARACTERISTIC DEEP-SEA TYPES. RHIZOPODS. 167 



Orbulina universa, a cosmopolitan species, dates back to the 

 lias and is very common in the tertiary. It is widely distributed 

 on the coralline and ooze of the Caribbean, and one of the 

 pelagic types most frequently found. Pourtales discovered that 

 bottom specimens of O. universa did not always consist of a 

 simple chamber, but generally included three or four chambers 

 (Fig. 510), resembling young Globigerinse more or less devel- 

 oped, and attached to the inside by slender spicules. Krohn 

 observed the same in living specimens. It seems probable that 

 the Globigerinae in the chamber are resorbed, and that the vis- 

 ible spherical chamber is the last segment, considered at one 

 time to be a special reproductive chamber, and capable of wide- 

 spread existence. The Globigerinse are eminently pelagic, some 

 of the genera exclusively so, and the shells when alive are thin 

 and transparent. 



The shell of Globigerina is composed of a series of hyaline 

 and perforated chambers of a spheroidal form, arranged in a 

 spiral manner, with the apertures of each chamber opening 

 round the umbilicus. The young shells are made up of fewer 

 and comparatively larger chambers. The tests of Globigerina 



Fig. 511. Fig. 511 a. Fig. 511 b. 



Globigerina bulloides. \ 6 - ( Go& -) 



bulloides (Figs. 511, 511 a, 511 b) and of Orbulina universa 



(Fig. 512) are among the most common deep-water rhizopods. 



Globigerina are spinous in their early stages, and probably more 



or less so when the shell has attained its full 



development, but the spines are of such extreme 



tenuity that, when taken with the tow-net, they 



are invariably broken. Bottom specimens have 



no spines, and these may be present perhaps only 



in the pelagic stage ; the delicate calcareous ^^ ,; nive 



spines, from four to five times the diameter of the Y- (Goes.) 



