EXPLANATION OF PLATE XLVIII. 



Figs. 1-5. SPIRIFER TENUIMARGINATUS Hall p. 355 



Pedicle, brachial, lateral, posterior and anterior views of a sulphur 

 cast of the holotype. (W. M., No. 14774.) 

 Keokiik limestone, Warsaw, Illinois. 



Figs. 6-16. SPIRIFER ROSTELLATUS Hall p. 353 



6-10. Pedicle, brachial, posterior, anterior and lateral views of the 

 holotype. (W. M., No. 6930.) 



Keokuk limestone, Warsaw, Illinois. 



11-14. Pedicle, brachial, anterior and lateral views of an internal 

 cast of a rather broad specimen. (D. K. G., No. 3201.) 



Residual chert, Richland Creek, Callaway Co., Missouri. 

 15-16. Pedicle and brachial views of an imperfect internal cast. 

 (YY. M., No. 339.) 



Residual chert, Springfield, Missouri. 



Figs. 17-21. SPIRIFER STRIATIFORMIS Meek p. 364 



17-20. Pedicle, brachial, anterior and lateral views of a nearly per- 

 fect specimen. (W. M., No. 13578.) 



Waverly Group, Medina, Ohio. 



21. Mew of an imperfect pedicle valve. (W. M., No. 5676.) 

 Choutcan limestone, Green County, Missouri. 



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