20 BULLETIN 10 4, UNITED STATES NATIONAL MUSEUM 



making up nearly or quite all of the exterior of the test. The aperture 

 becomes very complex. The last three genera were especially devel- 

 oped in the Upper Cretaceous and did not live beyond that period. 



Altogether there is a very definite series along a number of lines of 

 development, the fossil record agreeing well with the stages in devel- 

 opment shown in the individual. The microspheric form as is the 

 case with other families of the foraminifera shows the most nearly 

 complete stages in development. 



Most of the genera and species are at the present day characteristic 

 of warm shallow waters, very abundant about coral reefs in the 

 tropics. Some of the genera such as Pyrgo and Sigmoilina have 

 developed species which have become adapted to cold and deep water. 

 In brackish or very deep water there are developed thin, chitinous or 

 siliceous tests showing the added relationships of this family to the 

 Silicinidae and to the arenaceous group with their chitinous lining. 



A key is given to all the genera of the family regardless as to 

 whether they are recent or not. 



I. Test not divided into chambers, irregularly winding Agathammina. 



II. Test chambered. 



A. Test not reaching a triloculine stage. 



1. Quinqueloculine throughout. 



a. Aperture simple, with a simple tooth Quinqueloculina. 



b. Aperture cribrate. 



(1). Entirely calcareous, chambers completely involute. 



Miliola. 

 (2). Exterior arenaceous, chambers not completely involute. 



Schlumbergerina. 



2. Later chambers of various shapes. 



a. Later chambers two to a coil, laterally spreading. 



(1). Quinqueloculine stage prominent, flattened chambers few. 



Massilina. 

 (2). Quinqueloculine stage reduced, flattened chambers many. 



Spiroloculina. 

 (3). Quinqueloculine stage prominent, later chambers sigmoid. 



Sigmoilina. 



b. Later chambers more than two in a coil. 



(1). Aperture simple, with a broad tooth Nummoloculina. 



(2). Aperture cribrate Hauerina. 



c. Later chambers elongate. 



(1). Quinqueloculine stage prominent, uniserial chambers few. 



Articulina. 

 (2). Quinqueloculine stage reduced, uniserial chambers many- 



(a). Chambers indistinct, without a tooth Tubinella. 



(6). Chambers distinct, with a distinct tooth. _Nubeculina. 



B. Test reaching a triloculine stage but not a biloculine one. 



1. Triloculine throughout. 



a. Interior simple, aperture with a simple or bifid tooth. .Triloculina. 



b. Interior with secondary growth, aperture cribrate Trillina. 



2. Later stages in one plane, not uncoiled Flintina. 



3. Later stages uncoiling and becoming uniserial Ptychomiliola. 



