THE FORAMINIFERA 



117 



Schlumberger has shown (50) that in Siphogenerina glalra 

 the microspheric form tapers to a point at the initial end, and has 

 9-10 chambers arranged alternately before the uniserial mode of 

 growth is assumed ; while the megalospheric form is short, begins 

 abruptly with a large central chamber, and has only three alternat- 

 ing chambers prior to the uniserial chambers. 



ORDER Globigerinidea. 



In this group, as defined by Brady, the tests consist of a few 

 inflated chambers arranged in a spiral manner. The members of 

 it inhabit the surface waters of the ocean, furnishing an important 



FIG. 49 



Gldbigerina bulloides, d'Orb. (to left), and Orbulina universa, d'Orb. (to right). (From 

 Rliumbler, 38.) The figure of G. bulloides represents the test as seen from the superior sur- 

 face. The specimen departs from the normal in possessing an aperture on this aspect of the 

 terminal chamber. 



constituent of the pelagic fauna ; and their empty shells, falling to 

 the bottom, form the main constituent of the " Globigerina ooze " 

 (see p. 138). 



Globigerina bulloides, d'Orb. (Fig. 49), the most abundant species 

 of the genus, has globular chambers forming a "rotaline" test, 

 each opening by a separate orifice into the deep umbilical space 

 on the "inferior" 1 surface. The chambers increase rapidly in 

 size, as the series is followed, and there are three or four in the 

 terminal convolution. 



The walls of the chambers are perforated by pores, and 

 at first are thin and smooth. As the shell increases in thickness, 



1 See the characters of Rotalidae, p. 145. 



