PLATE XXVII— Cimlinued. 



Syuingothtris subcuspidatus, Hall. 



See Plate 26. 

 Fig. 18. A front view of the iiedicle-valve ; showing its exterior and elevation, with the baso-Luteral mar- 

 gins of the bi'achial valve. 



Keol^uk group. KeokuJc, Iowa. 



Genus SPIRIFER, Sowekby. 



Page 1. 



Spikifer Wortheni, Hall. 



Fig. 19. A view of the original specimen. 



Fig. 20. An enlargement of the external surface of the .shell. 



Upper Helderberg group. Near Hamburg, Illinois. 



