356 FORAMINIFERA 



double layer of chambers, and later a median layer is inter- 

 calated between the chambers of the lateral layers. The median 

 layer is composed of concentric rings of chambers, the chambers 

 of one ring alternating in position with those of adjacent rings. 

 The outer walls of the chambers are only slightly curved or are 

 nearly straight. The median chambers communicate with the 

 lateral chambers through apertures in the floors of the latter 

 and those in the periphery open to the outside through marginal 

 apertures which rather regularly alternate in position and are 

 arranged in one, two, three, or four rows. Both the roofs and 

 sides of the chambers are pierced by very fine perforations simi- 

 lar to those of the more typical orbitoids. The superficial or lat- 

 eral chambers are arranged in concentric rings, with those of 

 each ring alternating in position with those of adjacent rings. 

 Each chamber communicates with two chambers of both the 

 preceding and the succeeding ring. There are also cribriform 

 perforations. On the outer surface a network of lozenge-shaped 

 meshes is produced by the immediately underlying layer. Pillars, 

 which may be lamellate, may be formed and produce wavy 

 radiating costae. 

 Maestrichtian, 



