THE TEST 17 



Triloculina, and in the adult the broad tooth characteristic of 

 that species of Pyrgo. 



In the more primitive forms the aperture is but a simple 

 opening in the wall of the test (PI. 5, fig. 3). In most coiled 

 forms it is a simple opening between the base of the chamber wall 

 and the preceding whorl (PI. 10, fig. 6 6). In uncoiled forms, 

 the aperture tends to become terminal and to appear in the aper- 

 tural face itself finally becoming entirely terminal (PI. 20, fig. 

 12 a) . The same is true in the biserial forms such as the Textu- 

 lariidae and the uniserial forms that have developed from them 

 (See plate 11) . 



In forms that become much compressed so that the aperture 

 tends to become a very long narrow opening, there are partitions 

 built across the opening as in Peney'oplis (PI. 31, fig. 1) even 

 though the chamber itself is not divided into chamberlets. In 

 complex types in which the chambers are subdivided into cham- 

 berlets, the apertures are usually multiple. Toward the end of 

 development in many different groups there is a decided ten- 

 dency to have multiple apertures instead of a single one. This 

 can be seen by referring to the various plates showing develop- 

 ment (Pis. 13, 19, 37). Many species in their adult chamber 

 have numerous large pores or supplementary apertures, es- 

 pecially those that have become pelagic in habit. 



The forms which have become uniserial as a rule have 

 terminal apertures. These typically develop a cyclindrical neck 

 and often a phialine lip (PI. 36, figs. 13, 23), characters more 

 closely associated with mechanical form than with systematic 

 relationships. Parallelisms of this general type are abundant 

 in the foraminifera. 



In many foraminifera there is developed a tooth of some sort 

 in the aperture. This is usually an outgrowth of the side and 

 many become very complex. In the Miliolidae (PI. 18) and the 

 Valvulinidae (PI, 12) some of these forms will be found. In 

 the Bulminidae and the Ellipsoidinidae there are frequently 

 tooth-like structures in the aperture that are related to the 

 tubular structures connecting the apertures within the chambers 

 themselves. 



The Lagenidae and Polymorphinidae have developed a peculiar 

 radiate aperture that is very distinctive. The primitive aper- 

 ture as seen in Robulus is simple. Above this simple aperture 



