I'l.ATK XXI— Continued. 



Genus SPIRIFEK. Sowkkby. 



Page I. 



Spikifer Eudoka, Hull. 



Fig-. 19. An internal cast ; showinpr the imprefisions of the dental plates. 

 Fig-. 20. A prcilile of the same. 



Niagara group. liacinr, Wisconsin. 

 Fig. 21. Tiie exterior of tlie pedicle-valve; showing the lineale surface. 

 Fig. 29. An enlargement of the surface of the .<!ame specimen. 



Niagara group. Waldron, Indiana. 



SriUIFER MACKOPLEURA, Coiliail. 



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



Lower Helder'oerg group. Sclio?iarie, N. T. 

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



Fig. 2.^?. The inteiior of a portion of the pedicle-valve ; showing the callosity of the dellhyriuin. 

 Fig. 24. An internal cast of the pedicle-valve ; showing the impi-essions of the ]iedicle, adductor and 

 diductor muscles. 



Lower Helderberg group. T/ie Helderbergs, N. T. 



