144 FORAMINIFERA 



Test planispiral, the tubular chamber partially divided, the 

 sides of the test built up with secondary shell material ; wall 

 arenaceous, with much cement; aperture circular at the end of 

 the tubular chamber. 



Lias. 



This is an especially interesting family as it is closely related 

 to the Miliolidae, especially the more primitive characters in that 

 group. The character of developing a siliceous test is found in 

 the primitive Miliolidae as well as in the Silicinidae. 



FAMILY 16. MILIOLIDAE 



Test typically coiled about an elongate axis in various planes, 

 at least in the microspheric young of even the specialized genera ; 

 chambers usually a half coil in length, simple in most genera in 

 a few with complex interiors, in the adult of many forms vari- 

 ously arranged ; wall normally calcareous, imperforate, in some 

 species of the more primitive genera with included sand grains 

 on the exterior, under acid conditions developing a siliceous or 

 chitinous test; aperture terminal, simple or cribrate, usually 

 with a tooth. 



KEY TO THE GENERA 



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



II. Test chambered. 



A. Test not reaching a triloculine stage. 



1. Quinquelocuiine throughout. 



a. Aperture simple, with a simple tooth Qiimquelocnliyia. 



b. Aperture cribrate. 



(1). Entirely calcareous, chambers completely involute. 



Mtliola. 

 (2). Exterior arenaceous, chambers not completely in- 

 volute Schliimbergerina. 



2. Later chambers of various shapes. 



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



(1). Quinquelocuiine stage prominent, flattened chambers 



few Massilina. 



(2). Quinquelocuiine stage reduced, flattened chambers 



many Spiroloculina. 



(3). Quinquelocuiine stage prominent, later chambers 



sigmoid Sigmoilina. 



