PLATE XXVII— Continaed. 



Syringothyris subcuspidatus, Hall. 



See Plate 26. 

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

 gins of the brachial valve. 



Keokuk group. Keokuk, Imoa. 



Genus SPIRIFER, Sowerby. 



Page 1. 



Spirifer Wortheni, Hall. 



Fig. 19. A view of the original specimen. 



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



Upper Helderberg gi-oup. Near Hamburg, Illinois. 



