66 University of Michigan 



PLATE III 



Elliptic. Hinge armature. 



Figure 22. B. Viebmanni cuatotolapamensis. Hinge armature of 

 right valve of type (figure 22, plate IV). 



Figure 15. E. plexus distinctus. Hinge armature of right valve 

 of figure 15, plate II. Young shell. 



Figure 11. E. plexus distinctus. Hinge armature of right valve 

 of figure II, plate II. Old shell. 



