213 



CHAPTER XV 



THE FAMILY EOTALIID^ 



The shell-structure of the Foraminifera constituting 

 the Family Rotaliid^ is essentially calcareous, hya- 

 line, and perforate. The tests are sometimes found 

 adherent to other objects, but are more usually 

 free. Their chief character is the rotaline or spiral 

 form of the shell ; and the coil is generally asym- 

 metrical. To this method of growth there are some 

 exceptions, as in the acervuline genera, like Planor- 

 hulijia and Gijpsina, but which, however, show their 

 relationship to the more typical members of the 

 family by their rotaline contour in the earlier stages 

 of growth, occasionally only in those chambers formed 

 in the embryonic condition. 



The typical appearance of a Rotaline form is a 

 spiral series of chambers so arranged that on one 

 face, the superior, we have all the chambers visible ; 

 whilst on the other, the inferior face, only those of 

 the last whorl are seen. The aperture is usually 

 situated on this inferior surface. 



The more advanced types of shell-structure in 

 this family consist in the presence of a double w^all 

 to the chambers. There is sometimes a redundant 

 growth of shell- structure also present, which chiefly 



