448 



NATURE AND MAN. 



found to present a much simpler plan of structure ; the chamber- 

 lets being arranged in a single plane around the central nucleus, 



/ 



cr. 



^^^^^'^^^^'%''':S^'^^^^^ 



Fig. III. 

 Structure of Shelly Disk of Orbiioliies complanata. 



1. Edge of Disk, showing multiple series of marginal pores. 



2. Vertical Section, showing two superficial planes of chamberlets, separated 

 by intermediate columnar structure. 



3. Internal Structure : — a, superficial chamberlets ; b, b, columnar chamber- 

 lets of intermediate layer ; c, floors of superficial chamberlets, showing the 

 opening at each end into the annular gallery beneath ; d, annular galleries cut 

 transversely ; d', d", annular galleries laid open longitudinally ; e e,ff, oblique 

 stolon passages of the intermediate layer. 



those of each ring being connected by a single annular gallery. 



