216 FORAMINIFERA 



FAMILY 26. PENEROPLIDAE 



Test imperforate except the proloculum and second chamber 

 which are distinctly perforate, calcareous, in general planispiral 

 in the young, then becoming annular or uncoiling; chambers 

 typically divided into chamberlets in all but the most primitive 

 genera; aperture in the simpler forms slit-like, becoming 

 multiple in the complex forms or rounded and terminal in the 

 uncoiled forms. 



KEY TO THE GENERA 



I. Chambers simple, without chamberlets, close coiled at least in the 



young, becoming uncoiled in the adult. 



A. Test more or less compressed, mostly coiled. 



1. Aperture elongate, slit-like, or a linear series of rounded 



openings Peneroplis. 



2, Aperture dendritic Deridritina. 



B. Test mostly uncoiled except in the earliest stages, aperture 



terminal. 



1, Wall thick, chambers of equal size, aperture without a neck 



and lip Spirolina. 



2. Wall very thin, chambers usually enlarging as added, aperture 



typically with a neck and lip Monalysidium. 



II. Chambers divided into chamberlets. 



A. Annular chambers only in the adult if at all developed. 



1. Growing edge peripheral in the adult. 



a. Annular chambers not developed, chambers involute. 



Fallotia. 



b. Annular chambers in the adult, chambers in adult not 



involute Archaias. 



2. Growing edge meandering on the flat faces of the test. 



Meandropsina. 



B. Annular chambers very early developed. 



1. Chamberlets in a single plane. 



a. Not completely divided Praesorites. 



b. Completely divided Sorites. 



2. Chamberlets usually in two planes, aperture in one or two 



]jj^gg Amphisorus. 



3. Chamberlets complex, no lateral layers of shell material. 



a. Adjacent chambers in each annular chamber connecting. 



Marginopora. 



b. Adjacent chambers in each annular chamber not connect- 



j^o- Orbitolites. 



4. Chamberlets complex, flat sides of the test with a thick im- 



perforate layer Opertorbitolites. 



