NO. 4 FORAMINIFERA CUSHMAN 49 



to the umbilical region so that only the last formed whorl is visible, 

 chambers either inflated with depressed sutures bridged across at 

 regular intervals or the sutures may be limbate and the processes form 

 a regular series of elevated ridges connecting the sutures ; aperture 

 either a simple opening at the base of the apertural face of the chamber 

 or subdivided into a series of openings. 



Genus ARCHAEDISCUS H. B. Brady, 1873 



Test lenticular, unsymmetrical, spirally coiled ; segments irregularly 

 constricted and expanded to form chambers ; canal system and supple- 

 mentary sl^eleton wanting. 



Genus AMPHISTEGINA d'Orbigny, 1826 



Plate 13, fig. 4 



Test spiral, lenticular, more convex on one side than the other, the 

 last-formed volution usually covering the others, chambers wnth the 

 alar projections on one side simple, divided on the other side by deep 

 constrictions to form supplementary lobes ; wall thickened near the 

 umbilicus, usually smooth except near the aperture on the ventral side 

 where it is usually papillose, no true secondary canal system devel- 

 oped ; aperture on the ventral side at the base of the chamber, simple. 



Genus OPERCULINA d'Orbigny, 1826 

 Plate 13, fig. 5 



Test coiled, compressed, consisting of numerous chambers in three 

 or four volutions, bilaterally symmetrical, and all visible from either 

 side, not embracing, except in the early whorls, in face view very thin, 

 usually thickest at the umbonal region ; surface smooth or ornamented 

 with bosses; aperture single at the base of the apertural wall of the 

 chamber. 



Genus HETEROSTEGINA d' Orbigny, 1826 

 Plate 13, fig. 6 



Test compressed, especially the last-formed whorl, the early whorls 

 often embracing and fairly thick, lenticular in side view ; chambers 

 numerous, subdivided into chamberlets by transverse partitions and 

 visible from the exterior; secondary canal system developed and 

 comparable to Operculina; aperture consisting of a row of pores 

 on the outer face of , the chamber, one pore for each of the chamberlets. 



