PLATE XXI— Continued. 



Genus SPIRIFER, Sowerby. 



Page 1. 



Spikifek Eudoua, Hull. 



Fig. 19. An internal cast ; showing the inipi-essions of the dental plates. 

 Fig. 20. A profile of the same. 



Niagara group. Racine, Wisconsin. 

 Fig. 21. The exterior of the pedicle- val ve ; showing the lineate surface. 

 Fig. 29. An enlargement of the surface of the same sjiecimen. 



Niagara group. Waldron, Indiaim. 



Spikifeb macropleuka, Coiinid. 



Fig. 22. A dorsal view of a normal, mature individual ; showing the surface charactere. 



Lower Helderberg group. Schoharie, N. Y. 

 Fig. 27. An enlargement of the surface of the same specimen. 



Fig. 23. The interior of a portion of the pedicle-valve ; showing the callosity of the delthyrium. 

 Pig. 24. An internal cast of the pedicle-valve ; showing the impressions of the pedicle, adductor and 

 diductor muscles. 



Lower Helderberg group. The Helderbergs, N. Y. 



