EXPLANATION OF PLATE 12 



Figs. 1-3 Canm/a cormcw/ww (Miller) emend. Easton; plesiotypes ; x5 . . . . . . . p. 49 



1, Transverse section, ephebic stage ; thickened counter septa are characteristic. 



2, Transverse section, late ephebic stage ; note thickened counter septa and general with- 

 drawal of all septa from center (amplexoid retreat). 



3, Longitudinal section showing steeply tilted tabulae ; same specimen as 1. 



Figs. 4-8 Ample xus rockfordensis Miller and Gurley ; plesiotypes ; X 2.5 p. 48 



4, Longitudinal section showing wide spacing of tabulae ; University of Michigan 

 No. 23234. 



5, Transverse section, late ephebic stage ; thickened septa of cardinal quadrants and 

 amplexoid retreat are characteristic ; University of Michigan No. 23233. 



6, Transverse section, reversed, early ephebic stage ; thickened septa of cardinal quadrants, 

 extra-thickened cardinal septum, and extent of septa almost to center are character- 

 istic ; University of Michigan No. 23233. 



7, Transverse section, reversed, neanic stage ; all septa are thick ; University of Michigan 

 No. 23236. 



S. Transverse section, reversed, very late ephebic stage ; very short septa are character- 

 istic; very short minor septa present; University of Michigan No. 23234. 



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